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Research involving Lowell Observatory staff 2020
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Years: 2020 Bottom


  1. dal Ponte, M., Santiago, B., Carnero Rosell, A., et al., (including Kuehn, K.), 2020, MNRAS, 499, 5302, Increasing the census of ultracool dwarfs in wide binary and multiple systems using Dark Energy Survey DR1 and Gaia DR2 data
    We present the discovery of 255 binary and 6 multiple system candidates with wide (> 5 arcsec) separation composed by ultracool dwarfs (UCDs) companions to stars, plus nine double ultracool dwarf systems. These systems were selected based on common distance criteria. About 90 per cent of the total sample has proper motions available and 73 per cent of the systems also satisfy a common proper motion criterion. The sample of ultracool candidates was taken from the Dark Energy Survey (DES) and the candidate stellar primaries are from Gaia DR2 and DES data. We compute chance alignment probabilities in order to assess the physical nature of each pair. We find that 174 candidate pairs with Gaia DR2 primaries and 81 pairs with a DES star as a primary have chance alignment probabilities $\lt 5{{\ \rm per\ cent}}$. Only nine candidate systems composed of two UCDs were identified. The sample of candidate multiple systems is made up of five triple systems and one quadruple system. The majority of the UCDs found in binaries and multiples are of early L type and the typical wide binary fraction over the L spectral types is $2\!-\!4{{\ \rm per\ cent}}$. Our sample of candidate wide binaries with UCDs as secondaries constitutes a substantial increase over the known number of such systems, which are very useful to constrain the formation and evolution of UCDs.
  2. Chen, Y., Liu, X., Liao, W., et al., (including Kuehn, K.), 2020, MNRAS, 499, 2245, Candidate periodically variable quasars from the Dark Energy Survey and the Sloan Digital Sky Survey
    Periodically variable quasars have been suggested as close binary supermassive black holes. We present a systematic search for periodic light curves in 625 spectroscopically confirmed quasars with a median redshift of 1.8 in a 4.6 deg2 overlapping region of the Dark Energy Survey Supernova (DES-SN) fields and the Sloan Digital Sky Survey Stripe 82 (SDSS-S82). Our sample has a unique 20-yr long multicolour (griz) light curve enabled by combining DES-SN Y6 observations with archival SDSS-S82 data. The deep imaging allows us to search for periodic light curves in less luminous quasars (down to r ~23.5 mag) powered by less massive black holes (with masses 108.5M) at high redshift for the first time. We find five candidates with significant (at >99.74 per cent single-frequency significance in at least two bands with a global p-value of ~7 10-4-3 10-3 accounting for the look-elsewhere effect) periodicity with observed periods of ~3-5 yr (i.e. 1-2 yr in rest frame) having ~4-6 cycles spanned by the observations. If all five candidates are periodically variable quasars, this translates into a detection rate of ${\sim }0.8^{+0.5}_{-0.3}$ per cent or ${\sim }1.1^{+0.7}_{-0.5}$ quasar per deg2. Our detection rate is 4-80 times larger than those found by previous searches using shallower surveys over larger areas. This discrepancy is likely caused by differences in the quasar populations probed and the survey data qualities. We discuss implications on the future direct detection of low-frequency gravitational waves. Continued photometric monitoring will further assess the robustness and characteristics of these candidate periodic quasars to determine their physical origins.
  3. Holler, B., Young, L., Grundy, W., et al., 2020, AGUFM, 2020, P032-0006, Comparative KBOlogy: The Dynamic Surfaces of Pluto and Triton
    Pluto, the largest Kuiper Belt dwarf planet, and Triton, Neptune's largest satellite and a former Kuiper Belt Object [1], are the largest known objects with rock/ice compositions found at or beyond Neptune's orbit. The similarities between Pluto and Triton provide a backdrop for the differences and a window into physical processes at work on icy surfaces.

    Seasonal transitions on Pluto and Triton are moving in opposite directions, with surface composition changes observed on both over 10+ years. Pluto is approaching N. hemisphere summer in 2029 while Triton entered S. hemisphere summer in 2000. Volatile N2 and CH4 band depths are decreasing on Pluto [2] and increasing on Triton [3]. This makes sense at first glance, but the reasons for these changes may be different.

    Increasing volatiles on Triton could indicate ongoing deposition or regions of past deposition being revealed in the N. hemisphere. Continued spectral observations of Triton over the coming years will provide clues to evaluate ongoing changes: A decrease in H2O band area would point to deposition, even if volatile band areas remain constant due to volatile transport. It remains to be seen if volatiles will be completely removed from the N. hemisphere of Pluto over the next decade, mimicking the current state of Triton's S. hemisphere [3]. Yearly observations of Pluto are critical in the coming years, as models predict the complete loss of volatiles from the N. hemisphere by 2030 [4]; "matched pairs" of spectra made at comparable sub-observer latitudes and longitudes will make yearly comparisons possible.

    The same strategy is not as critical for Triton due to the lack of a Sputnik Planitia-like feature that dominates the spectrum (evidence of a depleted volatile inventory compared to Pluto) and because non-volatile H2O absorption is constant with longitude [3]. The difference in volatile inventory between Pluto and Triton, a result of different formation histories [1,5], should play a key role in the magnitude of the band depth changes with time. These differences will be discussed in the context of spacecraft and other ground-based observations.


    [1] Agnor & Hamilton 2006. Nature 441, 192-194. [2] Grundy et al. 2014. Icarus 235, 220-224. [3] Holler et al. 2016. Icarus 267, 255-266. [4] Bertrand & Forget 2016. Nature 540, 86-89. [5] Canup 2011. AJ 141, 35.

  4. Sciamma-O'Brien, E., Roush, T., Salama, F., et al., (including Grundy, W.), 2020, AGUFM, 2020, P068-0001, Determination of the Complex Refractive Indices of Aerosol Analogs Formed at Low Temperatures with the NASA Ames Optical Constants Facility (OCF)
    The NASA Ames COsmic SImulation Chamber (COSmIC) [1] is a unique experimental facility that allows: 1) cooling a gas mixture to low temperature (150 K) in a jet expansion before inducing chemistry by plasma; and 2) controlling the extent of the chemical reactions by employing a pulsed plasma discharge. This enables the study of the early stages of aerosol production, as well as specific chemical pathways in planetary environments (e.g. Titan's and Pluto's atmospheres). Both the gas and solid products can be studied. For a decade COSmIC has been used to simulate Titan's atmospheric chemistry at low, Titan-like temperature [2]. New developments on the COSmIC facility are investigating formation of aerosols in tenuous, or transitory, atmospheres of other icy bodies [3-5], as well as cool exoplanets atmospheres having a hydrocarbon component, that results in formation of hazes and/or surface deposits of refractory materials.

    The new Ames Optical Constants Facility enables determination of the aerosol analogs' complex refractive indices, n and k, from 0.59 to 200 m [2]. Here we report efforts of determining n and k from ex-situ transmission measurements of solid samples produced from binary N2-CH4 and Ar-CH4, and tertiary N2-CH4-C2H2 and Ar-CH4-C2H2 gas mixtures in COSmIC, and deposited onto various substrates. A computational technique [6] that addresses interference fringes observed in the laboratory transmission data, particularly at wavelengths < 3 m, has been implemented and applied to determine n and k for the samples. At visible and near-infrared wavelengths (0.4-1.6 m) the deposit thickness, and its variation, as well as n and k were determined by a commercial entity. These data provide the ability to compare results, from independent methods, in the region of overlap between the two approaches.


    This research is supported by NASA's Science Mission Directorate SERA Directed Work Package. The authors acknowledge the outstanding technical support of R. Walker and E. Quigley.

    [1] Salama F. et al., IAU Proc., 13 (S332), 364-369, 2017.

    [2] Sciamma-O'Brien, E. et al., IAU Proc. (S350), 2020.

    [3] Grundy, W. et al. Icarus 314, 232-245, 2018.

    [4] Cook, J. C., et al. Icarus 331, 148-169, 2019.

    [5] Bertrand, T. and Forget, F. Icarus 287, 72-86, 2017.

    [6] Swanepoel, R., J. Phys. E: Sci. Instr., 16, 1214-1222, 1983.

  5. Cartwright, R., Beddingfield, C., Nordheim, T., et al., (including Grundy, W.), 2020, AGUFM, 2020, P074-04, Evidence for ammonia-bearing species on the Uranian satellite Ariel supports recent geologic activity
    The Voyager 2 encounter with the Uranian system revealed that the surface of Ariel exhibits many geologic landforms with unusual morphologies. The morphologies and estimated flow rheologies of these features are consistent with emplacement of ammonia (NH3) rich cryolavas on Ariel. NH3 is an efficient antifreeze agent when mixed with liquid H2O, allowing icy bodies to retain subsurface salty oceans for longer periods of time compared to "pure" H2O oceans. Because Voyager 2 was not equipped with a near-infrared mapping spectrometer, the composition of these geologic features is unknown. Recent ground-based telescope observations have detected spectral hints of a 2.2 m band on Ariel, which has been attributed to NH3-bearing species on other icy bodies, including Pluto and its moons Charon, Nix, and Hydra. However, the spatial distribution and spectral signature of the 2.2-m band on Ariel have not been previously investigated, limiting our ability to interpret its origin.

    We analyzed 32 ground-based telescope spectra of Ariel, spanning a wide range of sub-observer longitudes and latitudes. We measured the area and depth of the 2.2-m band, finding that ten spectra display prominent 2.2-m features (> 2 measurements). We found no discernable spatial trends in the distribution of the 2.2-m band, unlike the distribution of CO2 ice and H2O ice, which display significant hemispherical asymmetries on Ariel. Furthermore, we compared the Ariel spectra displaying the strongest 2.2-m bands to laboratory spectra of different NH3-bearing species, finding that NH3-H2O solutions and NH3-hydrates provide the best match to its spectral signature. We also found evidence for a 2.24-m band in four spectra, with a spectral signature most consistent with NH3 ice.

    The possible presence of NH3 is intriguing given that this constituent should be removed by energetic electrons (~1 MeV) over geologically short timescales. Consequently, the hints of NH3 detected on Ariel might result from geologic activity in the fairly recent past (< 2 Ga, based on regional crater density estimates), perhaps including emplacement of NH3-rich cryolavas. Similar connections have been made between the presence of NH3 and possible cryovolcanic features on Pluto, suggesting that NH3 might be a useful tracer of endogenic activity on some icy bodies.

  6. Kingsley, J., Strittmatter, P., Gonzales, K., et al., (including Kingsley, B.), 2020, SPIE, 11445, 114453K, A domeless, mobile 2-meter telescope
    There are many astronomical, interferometric and space situational awareness applications for single and multiple 2-meter aperture optical and infrared mobile telescopes that are low cost, can be easily transported and quickly deployed at a variety of sites. A design concept is presented for a trailermounted 2-meter telescope with a novel micro-enclosure that allows the telescope to be moved and deployed quickly for observations. The telescope is protected from adverse weather using a weatherproof telescope tube instead of a conventional dome or enclosure. It has Cassegrain, Nasmyth and coude foci suitable for astronomical, interferometric, space situational awareness, and laser communications applications, and is designed for replication at low cost. An initial implementation is being developed to explore the performance of such a telescope using re-purposed primary and secondary mirrors and other components from the MAGNUM telescope.
  7. Cornelius, F., Sweaton, M., Hardesty, B., et al., (including Collins, M., Levine, S.), 2020, SPIE, 11445, 114457I, Status and performance of Lowell Observatory's Lowell Discovery Telescope's active optical support system
    Lowell Observatory's Lowell Discovery Telescope (LDT) is a 4.3-m telescope designed and constructed for optical and near infrared astronomical observation. We examine the performance of the primary and secondary mirror support systems during scientific operations, over the first six years of science operations. During that time we have redesigned the sacrificial pins in the primary mirror lateral support system, and developed a method to re-calibrate the load cell sensors used in both the primary and secondary mirror supports.
  8. Kuehn, K., Kuhlmann, S., Ellis, S., et al., (including Caldwell-Meurer, H.), 2020, SPIE, 11451, 114516A, Application of atmospheric OH suppression technology to ground-based infrared astronomy
    We seek to advance the capabilities of photonic technologies in support of ground-based infrared astronomy. Currently, observers in this field suffer from an irreducible background generated by emission from OH (hydroxyl) molecules in the upper atmosphere. However, if narrow-band notch filters could be incorporated into the optical path of astronomical instruments prior to any optical elements that would spectrally broaden such emission lines, then this background could be effectively suppressed with very little accompanying loss of signal from the astronomical sources of interest. Micron-scale ring resonators are one technology that provides a promising method of generating such notch filters. Building on our previous efforts in astrophotonic technology development, our current goals are 1) to optimize the design of ring resonators so that the notch filters they create provide greatest suppression at the wavelengths of the most prominent OH lines, and 2) to optimize the coupling of the resonator-equipped silicon devices with the input fibers (from the sky) and output fibers (to the spectrograph and detector) such that the throughput losses do not completely eliminate the signal-to-noise improvement gained from the OH suppression. Theoretical estimates show that suppression (by 20-40dB) of the most prominent OH lines improves the signal to noise of near-IR observations by a factor of 5 or more - this is similar in effect to turning a telescope with a 1m aperture into a telescope with a 5m aperture!
  9. Neugent, K., Levesque, E., Massey, P., et al., 2020, ApJ, 905, 83, Erratum: "The Red Supergiant Binary Fraction of the Large Magellanic Cloud" (2020, ApJ, 900, 118)
    No abstract found.
  10. Scowen, P., Ardila, D., Jensen, L., et al., (including Llama, J.), 2020, SPIE, 11444, 114440A, SPARCS payload assembly, integration, and test update
    The Star-Planet Activity Research CubeSat (SPARCS) is a 6U CubeSat under construction that is devoted to the photometric monitoring of M stars in the far-UV (FUV) and near-UV (NUV), to measure the time-dependent spectral slope, intensity and evolution of low-mass star high-energy radiation. We report on the progress made in the assembly, integration and test of the instrument payload at Arizona State University using a custom TVAC chamber and optical stimulus that provides calibration light sources and the custom contamination control environment that the FUV demands. The payload consists of a custom 90mm clear aperture telescope developed by Hexagon/Sigma Space, combined with a dichroic plate to separate the FUV and NUV beams developed by Teledyne Acton and Materion, married with twin focal plane array cameras separately optimized for their bandpasses as developed by JPL.
  11. van Belle, G., Clark, J., Armstrong, J., et al., (including Pugh, T., Clark, W., Green, N., Jones, K., Kingsley, B., Kurtz, P., Schilperoort, A.), 2020, SPIE, 11446, 1144608, The Navy Precision Optical Interferometer: two years of development towards large-aperture observations
    We have been pursuing a comprehensive program of improving high-resolution imaging at the Navy Precision Optical Interferometer (NPOI) hosted at Lowell Observatory's Anderson Mesa site, for the purpose of spatially resolved observations of faint objects at scales down to less than 1 milliarcsecond. This activity at NPOI is being implemented with two primary phases. First, the `PALANTIR' upgrade of NPOI is augmenting the existing telescope array with three 1-meter PlaneWave PW1000 telescopes. These telescopes are housed in mobile domes for rapid relocation around the array, and are being augmented with adaptive optics. Second, we are implementing a `NPOI Plus-Up' plan which is modernizing the array infrastructure and streamlining its operations. All of these activities are being carried out as our current operations are continuing.
  12. Clark, C., van Belle, G., Horch, E., et al., (including Hartman, Z., Collins, M., von Braun, K., Gehring, J.), 2020, SPIE, 11446, 114462A, The optomechanical design of the Quad-camera Wavefront-sensing Six-channel Speckle Interferometer (QWSSI)
    The Quad-camera Wavefront-sensing Six-channel Speckle Interferometer (QWSSI) is a new speckle imaging instrument available on the 4.3-m Lowell Discovery Telescope (LDT). QWSSI is built to efficiently make use of collected photons and available detector area. The instrument images on a single Electron Multiplying CCD (EMCCD) at four wavelengths in the optical (577, 658, 808, and 880nm) with 40nm bandpasses. Longward of 1m, two imaging wavelengths in the NIR are collected at 1150 and 1570nm on two InGaAs cameras with 50nm bandpasses. All remaining non-imaging visible light is then sent into a wavefront EMCCD. All cameras are operated synchronously via concurrent triggering from a timing module. With the simultaneous wavefront sensing, QWSSI characterizes atmospheric aberrations in the wavefront for each speckle frame. This results in additional data that can be utilized during post-processing, enabling advanced techniques such as Multi-Frame Blind Deconvolution. The design philosophy was optimized for an inexpensive, rapid build; virtually all parts were commercial-off-the-shelf (COTS), and custom parts were fabricated or 3D printed on-site. QWSSI's unique build and capabilities represent a new frontier in civilian high-resolution speckle imaging.
  13. van Belle, G., Hillsberry, D., Kloske, J., et al., 2020, SPIE, 11446, 114462K, Optimast structurally connected interferometry enabled by in-space robotic manufacturing and assembly
    Future goals for astrophysics at the frontiers of high spatial resolution demand synthetic apertures significantly larger than the current or upcoming generations of single-aperture space observatories. Space-based interferometry enabled by in-space manufacturing delivers cost-effective observation of faint objects at unprecedented levels of angular resolution. Using the Made In Space (MIS) Optimast technology, a simple, two aperture Structurally Connected Interferometer (SCI) can be produced via in-space Additive Manufacturing (AM) technology. Optimast enables the manufacturing and deployment of small interferometric apertures at the tips of two large primary trusses unconstrained by launch loads or volume restrictions that meet science requirements for high angular resolutions, in the milliarcsecond regime. The LightBeam mission concept enabled by this capability has a wide range of ground-breaking science capabilities, including: measuring the sizes, shapes, and surface morphology of single asteroids, and binary asteroid orbits; imaging of young stellar object disk sculpting in the terrestrial planet regime; and probing the inner regions of active galactic nuclei. Space-based deployment of an interferometer unconstrained by the turbulent atmosphere will increase the sensitivity reach of such an instrument relative to its ground-based counterparts by a factor of 1,000 or more.
  14. Pandey, S., Krause, E., Jain, B., et al., (including Kuehn, K., DES Collaboration), 2020, PhRvD, 102, 123522, Perturbation theory for modeling galaxy bias: Validation with simulations of the Dark Energy Survey
    We describe perturbation theory (PT) models of galaxy bias for applications to photometric galaxy surveys. We model the galaxy-galaxy and galaxy-matter correlation functions in configuration space and validate against measurements from mock catalogs designed for the Dark Energy Survey (DES). We find that an effective PT model with five galaxy bias parameters provides a good description of the 3D correlation functions above scales of 4 Mpc /h and z <1 . Our tests show that at the projected precision of the DES Year 3 analysis, two of the nonlinear bias parameters can be fixed to their coevolution values, and a third (the k2 term for higher derivative bias) set to zero. The agreement is typically at the 2% level over scales of interest, which is the statistical uncertainty of our simulation measurements. To achieve this level of agreement, our fiducial model requires using the full nonlinear matter power spectrum (rather than the one-loop PT one). We also measure the relationship between the nonlinear and linear bias parameters and compare them to their expected coevolution values. We use these tests to motivate the galaxy bias model and scale cuts for the cosmological analysis of the Dark Energy Survey; our conclusions are generally applicable to all photometric surveys.
  15. Hinkle, K., Lebzelter, T., Fekel, F., et al., (including Prato, L.), 2020, ApJ, 904, 143, The M Supergiant High-mass X-Ray Binary 4U 1954+31
    The X-ray binary 4U 1954+31 has been classified as a low-mass X-ray binary containing an M giant and a neutron star (NS). It has also been included in the rare class of X-ray symbiotic binaries. The Gaia parallax, infrared colors, spectral type, abundances, and orbital properties of the M star demonstrate that the cool star in this system is not a low-mass giant but a high-mass M supergiant. Thus, 4U 1954+31 is a high-mass X-ray binary (HMXB) containing a late-type supergiant. It is the only known binary system of this type. The mass of the M I is ${9}_{-2}^{+6}$ M giving an age of this system in the range 12-50 Myr with the NS no more than 43 Myr old. The spin period of the NS is one of the longest known, 5 hr. The existence of M I plus NS binary systems is in accord with stellar evolution theory, with this system a more evolved member of the HMXB population.
  16. Fedorets, G., Micheli, M., Jedicke, R., et al., (including Moskovitz, N., Devogele, M.), 2020, AJ, 160, 277, Establishing Earth's Minimoon Population through Characterization of Asteroid 2020 CD3
    We report on our detailed characterization of Earth's second known temporary natural satellite, or minimoon, asteroid 2020 CD3. An artificial origin can be ruled out based on its area-to-mass ratio and broadband photometry, which suggest that it is a silicate asteroid belonging to the S or V complex in asteroid taxonomy. The discovery of 2020 CD3 allows for the first time a comparison between known minimoons and theoretical models of their expected physical and dynamical properties. The estimated diameter of ${1.2}_{-0.2}^{+0.4}$ m and geocentric capture approximately a decade after the first known minimoon, 2006 RH120, are in agreement with theoretical predictions. The capture duration of 2020 CD3 of at least 2.7 yr is unexpectedly long compared to the simulation average, but it is in agreement with simulated minimoons that have close lunar encounters, providing additional support for the orbital models. 2020 CD3's atypical rotation period, significantly longer than theoretical predictions, suggests that our understanding of meter-scale asteroids needs revision. More discoveries and a detailed characterization of the population can be expected with the forthcoming Vera C. Rubin Observatory Legacy Survey of Space and Time.
  17. Smith, M., D'Andrea, C., Sullivan, M., et al., (including Kuehn, K.), 2020, AJ, 160, 267, First Cosmology Results using Supernovae Ia from the Dark Energy Survey: Survey Overview, Performance, and Supernova Spectroscopy
    We present details on the observing strategy, data-processing techniques, and spectroscopic targeting algorithms for the first three years of operation for the Dark Energy Survey Supernova Program (DES-SN). This five-year program using the Dark Energy Camera mounted on the 4 m Blanco telescope in Chile was designed to discover and follow supernovae (SNe) Ia over a wide redshift range (0.05 < z < 1.2) to measure the equation-of-state parameter of dark energy. We describe the SN program in full: strategy, observations, data reduction, spectroscopic follow-up observations, and classification. From three seasons of data, we have discovered 12,015 likely SNe, 308 of which have been spectroscopically confirmed, including 251 SNe Ia over a redshift range of 0.017 < z < 0.85. We determine the effective spectroscopic selection function for our sample and use it to investigate the redshift-dependent bias on the distance moduli of SNe Ia we have classified. The data presented here are used for the first cosmology analysis by DES-SN ("DES-SN3YR"), the results of which are given in Dark Energy Survey Collaboration et al. The 489 spectra that are used to define the DES-SN3YR sample are publicly available at https://des.ncsa.illinois.edu/releases/sn.
  18. Oszkiewicz, D., Troianskyi, V., Fohring, D., et al., (including Skiff, B., Moskovitz, N., Devogele, M., Gustafsson, A.), 2020, A&A, 643, A117, Spin rates of V-type asteroids
    Context. Basaltic V-type asteroids play a crucial role in studies of Solar System evolution and planetesimal formation. Comprehensive studies of their physical, dynamical, and statistical properties provide insight into these processes. Thanks to wide surveys, currently there are numerous known V-type and putative V-type asteroids, allowing a detailed statistical analysis.
    Aims: Our main goal is to analyze the currently available large sample of V-type spin rates, to find signatures of the non-gravitational Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect among the different V-type populations, and to estimate the spin barrier and critical density for V-type asteroids. Our intention is to increase the pool of information about the intriguing V-types.
    Methods: We collected rotational periods from the literature for spectrally confirmed V-types, putative V-types, and Vesta family members. Through spectroscopic observations we confirmed their taxonomic type and verified the high confirmation rates of the putative V-types. We combined the collected periods with periods estimated in this manuscript and produced rotational frequency distributions. We determined the spin barrier in the frequency-light curve amplitude space for V-type asteroids.
    Results: We analyzed rotational periods of 536 asteroids in our sample. As expected, due to the small size of the objects analyzed, the frequency distributions for the Vesta family and the V-types outside the family are inconsistent with a Maxwellian shape. The Vesta family shows an excess of slow-rotators. V-types outside the family show an excess of both slow and fast rotators. Interestingly, we found that the population of V-types outside the Vesta family shows a significant excess of fast rotators compared to the Vesta family. The estimated critical density for V-type asteroids exceeds c = 2.0 g cm3, which surpasses the previous estimates.
    Conclusions: We demonstrated that V-type asteroids have been influenced by the thermal radiation YORP effect and that their critical spin rate is higher than for C-type asteroids. The population of V-types outside the Vesta family shows a significant excess of fast rotators compared to the Vesta family. We hypothesize that the objects that evolved from the Vesta family though the Yarkovsky drift are also more susceptible to the YORP effect. Objects for which YORP has not yet had enough time to act and those that are more YORP resistant will be left in the family, which explains the relatively small proportion of fast rotators being left. The YORP timescale must thus be similar to the migration timescale for those objects.
  19. Noll, K., Brown, M., Buie, M., et al., (including Grundy, W.), 2020, hst, 16452, Is the Lucy Mission Target (52246) Donaldjohanson a Binary?
    (52246) Donaldjohanson is a Main Belt asteroid target of opportunity that the Lucy mission will fly by in April 2025. In August 2020 it was revealed to have an exceptionally high amplitude and long period lightcurve. We propose here to test the possibility that this extreme lightcurve is produced by a synchronous binary. Such a system can explain both the amplitude and period with physically reasonable component shapes. The observations will take advantage of the only opportunity prior to 2025 when such a binary could be resolved by HST during the unusually close perihelic opposition in December 2020. The identification of a binary impacts the choice of target acquisition software to be used by the Lucy spacecraft during flyby.
  20. Pereira, M., Palmese, A., Varga, T., et al., (including Kuehn, K.), 2020, MNRAS, 498, 5450, masses: weak-lensing calibration of the Dark Energy Survey Year 1 redMaPPer clusters using stellar masses
    We present the weak-lensing mass calibration of the stellar-mass-based mass proxy for redMaPPer galaxy clusters in the Dark Energy Survey Year 1. For the first time, we are able to perform a calibration of at high redshifts, z > 0.33. In a blinded analysis, we use ~6000 clusters split into 12 subsets spanning the ranges 0.1 z < 0.65 and up to ${\sim} 5.5 \times 10^{13} \, \mathrm{M}_{\odot }$, and infer the average masses of these subsets through modelling of their stacked weak-lensing signal. In our model, we account for the following sources of systematic uncertainty: shear measurement and photometric redshift errors, miscentring, cluster-member contamination of the source sample, deviations from the Navarro-Frenk-White halo profile, halo triaxiality, and projection effects. We use the inferred masses to estimate the joint mass--z scaling relation given by $\langle M_{200c} | \mu _{\star },z \rangle = M_0 (\mu _{\star }/5.16\times 10^{12} \, \mathrm{M_{\odot }})^{F_{\mu _{\star }}} ((1+z)/1.35)^{G_z}$. We find $M_0= (1.14 \pm 0.07) \times 10^{14} \, \mathrm{M_{\odot }}$ with $F_{\mu _{\star }}= 0.76 \pm 0.06$ and Gz = -1.14 0.37. We discuss the use of as a complementary mass proxy to the well-studied richness for: (i) exploring the regimes of low z, < 20 and high , z ~ 1; and (ii) testing systematics such as projection effects for applications in cluster cosmology.
  21. Buckley-Geer, E., Lin, H., Rusu, C., et al., (including Kuehn, K.), 2020, MNRAS, 498, 3241, STRIDES: Spectroscopic and photometric characterization of the environment and effects of mass along the line of sight to the gravitational lenses DES J0408-5354 and WGD 2038-4008
    In time-delay cosmography, three of the key ingredients are (1) determining the velocity dispersion of the lensing galaxy, (2) identifying galaxies and groups along the line of sight with sufficient proximity and mass to be included in the mass model, and (3) estimating the external convergence ext from less massive structures that are not included in the mass model. We present results on all three of these ingredients for two time-delay lensed quad quasar systems, DES J0408-5354 and WGD 2038-4008 . We use the Gemini, Magellan, and VLT telescopes to obtain spectra to both measure the stellar velocity dispersions of the main lensing galaxies and to identify the line-of-sight galaxies in these systems. Next, we identify 10 groups in DES J0408-5354 and two groups in WGD 2038-4008 using a group-finding algorithm. We then identify the most significant galaxy and galaxy-group perturbers using the 'flexion shift' criterion. We determine the probability distribution function of the external convergence ext for both of these systems based on our spectroscopy and on the DES-only multiband wide-field observations. Using weighted galaxy counts, calibrated based on the Millennium Simulation, we find that DES J0408-5354 is located in a significantly underdense environment, leading to a tight (width $\sim 3{{\ \rm per\ cent}}$), negative-value ext distribution. On the other hand, WGD 2038-4008 is located in an environment of close to unit density, and its low source redshift results in a much tighter ext of $\sim 1{{\ \rm per\ cent}}$, as long as no external shear constraints are imposed.
  22. Gatti, M., Chang, C., Friedrich, O., et al., (including Kuehn, K.), 2020, MNRAS, 498, 4060, Dark Energy Survey Year 3 results: cosmology with moments of weak lensing mass maps - validation on simulations
    We present a simulated cosmology analysis using the second and third moments of the weak lensing mass (convergence) maps. The second moment, or variances, of the convergence as a function of smoothing scale contains information similar to standard shear two-point statistics. The third moment, or the skewness, contains additional non-Gaussian information. The analysis is geared towards the third year (Y3) data from the Dark Energy Survey (DES), but the methodology can be applied to other weak lensing data sets. We present the formalism for obtaining the convergence maps from the measured shear and for obtaining the second and third moments of these maps given partial sky coverage. We estimate the covariance matrix from a large suite of numerical simulations. We test our pipeline through a simulated likelihood analyses varying 5 cosmological parameters and 10 nuisance parameters and identify the scales where systematic or modelling uncertainties are not expected to affect the cosmological analysis. Our simulated likelihood analysis shows that the combination of second and third moments provides a 1.5 per cent constraint on S8 8(m/0.3)0.5 for DES Year 3 data. This is 20 per cent better than an analysis using a simulated DES Y3 shear two-point statistics, owing to the non-Gaussian information captured by the inclusion of higher order statistics. This paper validates our methodology for constraining cosmology with DES Year 3 data, which will be presented in a subsequent paper.
  23. Garcia, A., Morgan, R., Herner, K., et al., (including Kuehn, K.), 2020, ApJ, 903, 75, A DESGW Search for the Electromagnetic Counterpart to the LIGO/Virgo Gravitational-wave Binary Neutron Star Merger Candidate S190510g
    We present the results from a search for the electromagnetic counterpart of the LIGO/Virgo event S190510g using the Dark Energy Camera (DECam). S190510g is a binary neutron star (BNS) merger candidate of moderate significance detected at a distance of 227 92 Mpc and localized within an area of 31 (1166) square degrees at 50% (90%) confidence. While this event was later classified as likely nonastrophysical in nature within 30 hours of the event, our short latency search and discovery pipeline identified 11 counterpart candidates, all of which appear consistent with supernovae following offline analysis and spectroscopy by other instruments. Later reprocessing of the images enabled the recovery of six more candidates. Additionally, we implement our candidate selection procedure on simulated kilonovae and supernovae under DECam observing conditions (e.g., seeing and exposure time) with the intent of quantifying our search efficiency and making informed decisions on observing strategy for future similar events. This is the first BNS counterpart search to employ a comprehensive simulation-based efficiency study. We find that using the current follow-up strategy, there would need to be 19 events similar to S190510g for us to have a 99% chance of detecting an optical counterpart, assuming a GW170817-like kilonova. We further conclude that optimization of observing plans, which should include preference for deeper images over multiple color information, could result in up to a factor of 1.5 reduction in the total number of follow-ups needed for discovery.
  24. Marcialis, B., Vilas, F., Prato, L., et al., 2020, BAAS, 52, 0324, Obituary: Nadine G. Barlow (1958-2020)
    Barlow specialized in impact cratering processes, particularly on the planet Mars, and authored the textbook "Mars: An Introduction to its Interior, Surface, and Atmosphere". She spent much of her career at Northern Arizona University, eventually becoming Department Chair.
  25. Wiseman, P., Pursiainen, M., Childress, M., et al., (including Kuehn, K.), 2020, MNRAS, 498, 2575, The host galaxies of 106 rapidly evolving transients discovered by the Dark Energy Survey
    Rapidly evolving transients (RETs), also termed fast blue optical transients, are a recently discovered group of astrophysical events that display rapid luminosity evolution. RETs typically rise to peak in less than 10 d and fade within 30, a time-scale unlikely to be compatible with the decay of Nickel-56 that drives conventional supernovae (SNe). Their peak luminosity spans a range of -15 < Mg < -22.5, with some events observed at redshifts greater than 1. Their evolution on fast time-scales has hindered high-quality follow-up observations, and thus their origin and explosion/emission mechanism remains unexplained. In this paper, we present the largest sample of RETs to date, comprising 106 objects discovered by the Dark Energy Survey, and perform the most comprehensive analysis of RET host galaxies. Using deep-stacked photometry and emission lines from OzDES spectroscopy, we derive stellar masses and star formation rates (SFRs) for 49 host galaxies, and metallicities ([O/H]) for 37. We find that RETs explode exclusively in star-forming galaxies and are thus likely associated with massive stars. Comparing RET hosts to samples of host galaxies of other explosive transients as well as field galaxies, we find that RETs prefer galaxies with high specific SFRs (log (sSFR) ~ -9.6), indicating a link to young stellar populations, similar to stripped-envelope SNe. RET hosts appear to show a lack of chemical enrichment, their metallicities akin to long-duration gamma-ray bursts and superluminous SN host galaxies (12 + log (O/H) ~ 9.4). There are no clear relationships between mass or SFR of the host galaxies and the peak magnitudes or decline rates of the transients themselves.
  26. Grandis, S., Klein, M., Mohr, J., et al., (including Kuehn, K.), 2020, MNRAS, 498, 771, Validation of selection function, sample contamination and mass calibration in galaxy cluster samples
    We construct and validate the selection function of the MARD-Y3 galaxy cluster sample. This sample was selected through optical follow-up of the 2nd ROSAT faint source catalogue with Dark Energy Survey year 3 data. The selection function is modelled by combining an empirically constructed X-ray selection function with an incompleteness model for the optical follow-up. We validate the joint selection function by testing the consistency of the constraints on the X-ray flux-mass and richness-mass scaling relation parameters derived from different sources of mass information: (1) cross-calibration using South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) clusters, (2) calibration using number counts in X-ray, in optical and in both X-ray and optical while marginalizing over cosmological parameters, and (3) other published analyses. We find that the constraints on the scaling relation from the number counts and SPT-SZ cross-calibration agree, indicating that our modelling of the selection function is adequate. Furthermore, we apply a largely cosmology independent method to validate selection functions via the computation of the probability of finding each cluster in the SPT-SZ sample in the MARD-Y3 sample and vice versa. This test reveals no clear evidence for MARD-Y3 contamination, SPT-SZ incompleteness or outlier fraction. Finally, we discuss the prospects of the techniques presented here to limit systematic selection effects in future cluster cosmological studies.
  27. Jones, T., Kim, J., Dowell, C., et al., (including Hamilton, R.), 2020, AJ, 160, 167, HAWC+ Far-infrared Observations of the Magnetic Field Geometry in M51 and NGC 891
    Stratospheric Observatory for Infrared Astronomy High-resolution Airborne Wideband Camera Plus polarimetry at 154 m is reported for the face-on galaxy M51 and the edge-on galaxy NGC 891. For M51, the polarization vectors generally follow the spiral pattern defined by the molecular gas distribution, the far-infrared (FIR) intensity contours, and other tracers of star formation. The fractional polarization is much lower in the FIR-bright central regions than in the outer regions, and we rule out loss of grain alignment and variations in magnetic field strength as causes. When compared with existing synchrotron observations, which sample different regions with different weighting, we find the net position angles are strongly correlated, the fractional polarizations are moderately correlated, but the polarized intensities are uncorrelated. We argue that the low fractional polarization in the central regions must be due to significant numbers of highly turbulent segments across the beam and along lines of sight in the beam in the central 3 kpc of M51. For NGC 891, the FIR polarization vectors within an intensity contour of 1500 $\mathrm{MJy}\,{\mathrm{sr}}^{-1}$ are oriented very close to the plane of the galaxy. The FIR polarimetry is probably sampling the magnetic field geometry in NGC 891 much deeper into the disk than is possible with NIR polarimetry and radio synchrotron measurements. In some locations in NGC 891, the FIR polarization is very low, suggesting we are preferentially viewing the magnetic field mostly along the line of sight, down the length of embedded spiral arms. There is tentative evidence for a vertical field in the polarized emission off the plane of the disk.
  28. Ji, A., Li, T., Hansen, T., et al., (including Kuehn, K.), 2020, AJ, 160, 181, The Southern Stellar Stream Spectroscopic Survey (S5): Chemical Abundances of Seven Stellar Streams
    We present high-resolution Magellan/MIKE spectroscopy of 42 red giant stars in seven stellar streams confirmed by the Southern Stellar Stream Spectroscopic Survey (S5): ATLAS, Aliqa Uma, Chenab, Elqui, Indus, Jhelum, and Phoenix. Abundances of 30 elements have been derived from over 10,000 individual line measurements or upper limits using photometric stellar parameters and a standard LTE analysis. This is currently the most extensive set of element abundances for stars in stellar streams. Three streams (ATLAS, Aliqa Uma, and Phoenix) are disrupted metal-poor globular clusters, although only weak evidence is seen for the light-element anticorrelations commonly observed in globular clusters. Four streams (Chenab, Elqui, Indus, and Jhelum) are disrupted dwarf galaxies, and their stars display abundance signatures that suggest progenitors with stellar masses ranging from 106 to 107 M. Extensive description is provided for the analysis methods, including the derivation of a new method for including the effect of stellar parameter correlations on each star's abundance and uncertainty. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.
  29. Smith, E., Logsdon, S., McLean, I., et al., (including Hamilton, R.), 2020, ApJ, 902, 118, A Survey of 3-5.4 m Emission from Planetary Nebulae Using SOFIA/FLITECAM
    Here we present the results of an airborne 3-5.4 m spectroscopic study of three young, carbon-rich planetary nebulae (PNs) IC 5117, PNG 093.9-00.1, and BD +30 3639. These observations were made using the grism spectroscopy mode of the First Light Infrared TEst CAMera (FLITECAM) instrument during airborne science operations on board NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA). The goal of this study is to characterize the 3.3 and 5.25 m polycyclic aromatic hydrocarbon (PAH) dust emission in PNs and study the evolution of PAH features within evolved stars before their incorporation into new stellar systems in star-forming regions. Targets were selected from Infrared Astronomical Satellite, Kuiper Airborne Observatory and Infrared Space Observatory source lists, and were previously observed with FLITECAM on the 3 m Shane telescope at Lick Observatory to allow direct comparison between the ground and airborne observations. We measure PAH emission equivalent width and central wavelength, classify the shape of the PAH emission, and determine the PAH/aliphatic ratio for each target. The 3.3 m PAH emission feature is observed in all three objects. PNG 093.9-00.1 exhibits NGC 7027-like aliphatic emission in the 3.4-3.6 m region while IC 5117 and BD +30 3639 exhibit less aliphatic structure. All three PNs additionally exhibit PAH emission at 5.25 m.
  30. Cartwright, R., Nordheim, T., Cruikshank, D., et al., (including Grundy, W.), 2020, ApJL, 902, L38, Evidence for Sulfur-bearing Species on Callisto's Leading Hemisphere: Sourced from Jupiter's Irregular Satellites or Io?
    We investigated whether sulfur-bearing species are present on the icy Galilean moon Callisto by analyzing eight near-infrared reflectance spectra collected over a wide range of sub-observer longitudes. We measured the band areas and depths of a 4 m feature in these spectra, which has been attributed to sulfur dioxide (SO2), as well as carbonates, in previously collected data sets of this moon. All eight spectra we collected display the 4 m band. The four spectra collected over Callisto's leading hemisphere display significantly stronger 4 m bands compared to the four trailing hemisphere spectra (>3 difference). We compared the central wavelength position and shape of Callisto's 4 m band to laboratory spectra of various sulfur-bearing species and carbonates. Our comparison demonstrates that Callisto's 4 m band has a spectral signature similar to thermally altered sulfur, as well as a 4.025 m feature attributed to disulfanide (HS2). Our analysis therefore supports the presence of S-bearing species on Callisto but is not consistent with the presence of SO2. The significantly stronger 4 m band detected on Callisto's leading hemisphere could result from collisions with H2S-rich dust grains that originate on Jupiter's retrograde irregular satellites or implantation of magnetospheric S ions that originate from volcanic activity on Io. Alternatively, S-bearing species could be native to Callisto and are exposed by dust collisions and larger impacts that drive regolith overturn, primarily on its leading side.
  31. Leung, Y., Zhang, Y., Yanny, B., et al., (including Kuehn, K.), 2020, RNAAS, 4, 174, The Diffuse Light Envelope of Luminous Red Galaxies
    We use a stacking method to study the radial light profiles of luminous red galaxies (LRGs) at redshift 0.62 and 0.25, out to a radial range of 200 kpc. We do not find noticeable evolution of the profiles at the two redshifts. The LRG profiles appear to be well approximated by a single Sersic profile, although some excess light can be seen outside 60 kpc. We quantify the excess light by measuring the integrated flux and find that the excess is about 10%a non-dominant but still nonnegligible component.
  32. Cartwright, R., Nordheim, T., Cruikshank, D., et al., (including Grundy, W.), 2020, DPS, 52, 106.05, What is the origin and composition of Callisto's 4-micron band?
    Spectra collected by the Near Infrared Mapping Spectrometer (NIMS) onboard the Galileo spacecraft determined that a variety of near-infrared absorption bands overprint the dominantly 'dirty' H2O ice spectral signature of Callisto's surface. One such absorption band centered near 4 m has been attributed to the presence of SO2 on Callisto, as well as on Europa and Ganymede. This 4-m feature is thought to originate from S-rich species that are erupted from volcanoes on Io, ionized, and subsequently transported in Jupiter's co-rotating plasma to the three icy Galilean moons. This process can explain the presence of the 4-m feature on the trailing hemispheres of Europa and Ganymede. On Callisto, however, the 4-m band is stronger on its leading hemisphere, hinting at a different origin for this band and/or different contributing species, possibly including carbonates. Complicating matters, the often low signal-to-noise and low resolving power (R ~40-200) of spectra collected by NIMS has limited our ability to interpret the origin and composition of the 4-m feature.

    To further investigate Callisto's 4-m band, we collected new near-infrared spectra with the SpeX spectrograph on NASA's Infrared Telescope Facility (~1.9-5.3 m, R ~2500), representing a significant improvement over the quality of the available NIMS spectra. These SpeX spectra show that the 4-m feature is significantly stronger on Callisto's leading hemisphere, supporting prior analysis of the distribution of the 4-m feature detected by NIMS. The central wavelength position of the feature we detected is shifted to 4.02 m, whereas the SO2 combination band (1 + 3) detected on Io is centered near 4.07 m, casting doubt on SO2 as the primary constituent contributing to Callisto's 4-m band. Our results are more consistent with other S-bearing species like H2S2 or HS2, which could be formed by charged particle radiolysis of hydrogen sulfide (H2S). Additionally, the spectral signature of carbonates like Na2CO3 can also provide a good match to the 4-m feature. The clear hemispherical asymmetry in the distribution of the 4-m band is consistent with in-falling dust grains from Jupiter's retrograde irregular satellites, which should contribute material primarily to Callisto's leading side. Alternatively, the species contributing to Callisto's 4-m band could be native to this moon and are exposed by dust particle collisions that spur regolith overturn, as well as larger impact events that sample greater depths into its subsurface.

  33. Schleicher, D., Knight, M., Skiff, B., 2020, DPS, 52, 111.05, A Smorgasbord of Recent Comet Narrowband Imaging and Photometry: Results from NEOWISE (C/2020 F3), ATLAS (C/2019 Y4), PanSTARRS (C/2017 T2), and 88P/Howell
    We will report on preliminary results from recent and upcoming narrowband filter imaging and photometry data of four comets obtained from Lowell Observatory in 2020. Comet NEOWISE (C/2020 F3) was the brightest object in more than a decade but only became accessible for us in late July. By that time, water production had decreased to 1.61029 molecules/s, while the dust-to-gas ratio was significantly lower than average as compared to our database. CN imaging exhibits a counter-clockwise spiral rotation with successive outward moving arcs implying a possible period of about 7-8 hr; however, variations in the spacing and brightness of arcs in early August suggests multiple jets might be present, with the actual period perhaps twice the apparent value. The rapidly brightening Comet ATLAS (C/2019 Y4) suffered a major fragmentation event in April, about a month prior to perihelion. Though characterized in the press as having disappeared, we obtained additional photometry and imaging of the remnants in mid-May; the images showed that fragmentation was continuing to take place with the location and brightness of features changing from night-to-night. Furthermore, a CN coma was observed nightly, suggesting that at least one fragment remained active.

    We began our observations of Comet PanSTARRS (C/2017 T2) in early October 2019 at a distance of 3.15 AU. By perihelion (1.61 AU), water production reached 61028 molecules/s, following an r-dependence log-log slope of -4.3, and a steeper slope thus far outbound. Although early imaging showed little in morphological features, CN imaging in June revealed a pair of apparently side-on jets; however, these were no longer evident just a month later. Comet 88P/Howell, the only Jupiter Family object in this group, continues to have relatively unfavorable apparitions though the current one is the best since its discovery. Between mid-May and mid-August, and still approaching perihelion, water production is following an extremely steep r-dependence of -9.1, possibly suggesting that a dominant, isolated source region is rapidly "moving" from winter to summer.

    These and additional results from our observing campaigns will be presented. This work is supported by NASA's Solar System Observations Program grant 80NSSC18K0856.

  34. Fraser, W., Schwamb, M., Bannister, M., et al., (including Thirouin, A.), 2020, DPS, 52, 203.01, Do less-red KBOs share origins with the C-type asteroids?
    Spectral surveys of the outer Solar System are starting to reveal the signatures of the early dispersal of the protoplanetesimal disk in the compositional-dynamical structure of the current planetesimal populations. The distribution of the known surface types of Kuiper Belt Objects (KBOs) are now being used to infer the compositional structure of the protoplanetesimal disk itself. We present a new idea regarding the compositional properties of KBOs that is predicated on the correlated optical-NIR colours of the two dynamically excited compositional classes. Specifically, we hypothesize that nearly all KBOs belonging to the less-red class share origins with some of the carbonaceous asteroids. We make use of the ugrizJ colours sample acquired by the Colours of the Outer Solar System Origins Survey to probe what compositional components are compatible with that idea. The broad spectral behaviour of the less-red class can be very well accounted for with a C-type spectrum mixed with many laboratory organic materials, such as tholins and other disordered organic ices, and requires the presence of water-ice. Variation of the non-carbonaceous additions can account for the correlated optical-NIR colours of KBOs. Increasing concentrations of the non-carbonaceous materials not only increases the optical spectral slopes, but increasingly masks the presence of the absorption features common to carbonaceous asteroids, which are seen on only the most neutral coloured KBOs, and produce nearly linear spectra like those observed. Within this model, Phoebe occupies a special category, possessing a high concentration of water-ice, and is completely devoid of the reddening agent. If this idea is true, it follows that the less-red class of KBOs are cosmogonically related to certain classes of carbonaceous asteroids, and likely shared a similar origin within the protoplanetesimal disk. As the Kuiper Belt is dominated by mass from the less-red class, our model implies that the majority of KBOs are simply reddened carbonaceous asteroids. Confirmation of this idea will come from the identification of the absorption features common to the C-types, which must also be common to most small KBOs, albeit with a more modest presence.
  35. Thirouin, A., Sheppard, S., 2020, DPS, 52, 203.03, Lightcurves of 2:1 Neptune resonant trans-Neptunian objects
    The 2:1 mean motion resonance with Neptune is located at about 47.8 AU and contains more than 85 known trans-Neptunian objects (TNOs). During Neptune's migration outward in the Solar System, TNOs from various locations were pushed and scattered into the 2:1 resonance giving this population of TNOs a large range of formation locations and surface colors. The 2:1 resonance with Neptune likely contains some TNOs of the dynamically Cold Classical population that show a very-red/ultra-red surface. Previously, we studied the rotational properties of the 3:2 resonance and dynamically Cold Classical TNOs and estimated the fraction of contact binaries in these two different dynamical populations (Thirouin and Sheppard, 2018, 2019). As the 3:2 and 2:1 resonances delimit the reservoir of dynamically Cold Classical TNOs in the main Kuiper belt, we obtain the lightcurves of a number of 2:1 TNOs in order to estimate the number of contact binaries and identify rotational differences between the various different highly evolved resonant populations and the more primitive Cold Classicals. For consistency and to limit observational biases, we designed a survey dedicated to the 2:1 resonant TNOs in the same way we did for the 3:2 and Cold Classical populations, using the Lowell Discovery Telescope and the Magellan telescope for lightcurves and color photometry. Here, we report some preliminary results on our observations of the 2:1 resonant TNOs which correspond to 58 percent of the 2:1 TNOs with a visual magnitude V less than 23.5mag. Sparse and complete lightcurves obtained are used to constrain the shape and rotational frequency distributions. We also compare the properties of the Cold Classicals to the various Neptune resonant populations. Using our results and the literature, we estimate that the 2:1 resonance could likely have fewer contact binaries than the 3:2 resonant population and are more consistent with our estimate for the dynamically Cold Classicals contact binary population. This low estimate for the 2:1 resonance contact binary percentage is not expected based on some binary survival modeling (Nesvorny and Vorouhlicky, 2019).

    This work is supported by the National Science Foundation (NSF), grant number 1734484.

  36. Strauss, R., Leiva, R., Keller, J., et al., (including Wasserman, L.), 2020, DPS, 52, 203.05, The sizes and albedos of Centaurs 2014 YY49, (342842) 2008 YB3, and 2013 NL24 from stellar occultation
    Trans-Neptunian objects (TNOs) are among our primitive neighbors. Their characterization can provide invaluable clues to understanding the formation and evolution of the early Solar System. Equally interesting to study are Centaurs, a transient population of dynamically unstable objects with orbits between those of the Jupiter and Neptune, understood to consist primarily of objects transitioning between TNOs and Jupiter family comets. Stellar occultation remains one of the most powerful techniques by which to obtain ground-truth measurements of the size and shape of TNOs and Centaurs. In the year 2019, stellar occultation measurements for three Centaurs were obtained by the Research and Education Collaborative Occultation Network (RECON), a citizen science telescope network designed to observe high-uncertainty occultations by these distant bodies. The objects measured, 2014 YY49, (342842) 2008 YB3, and 2013 NL24, are among the smallest objects in the outer Solar System measured by occultation.

    We present the methods and results of these three occultation efforts. We discuss the predictions, observations, and profile modeling techniques for the three centaurs. We will present the results of the modeling and the derived sizes and geometric albedos for each object, and for the brightest of these objects, 2008 YB3, we compare the occultation result with existing radiometric size estimates.

    Funding for RECON was provided by grants from NSF AST-1413287, AST-1413072, AST-1848621, and AST-1212159

  37. Moullet, A., Lellouch, E., Gurwell, M., et al., (including Grundy, W.), 2020, DPS, 52, 203.06, Thermal mapping of large KBO systems: putting the equal albedo assumption to the test
    High-resolution optical imaging of Kuiper-Belt objects has revealed that a surprisingly high fraction of objects are in binary or multiple systems, up to 70% in some dynamical populations. Several system formation mechanisms may be at play, such as capture, disruption, co-formation and collision, which are in turn indicative of the dynamical history of the region at large. Detailed studies of a systems' orbital properties as well as measurements of member sizes' ratios can help to distinguish across such formation mechanisms. Unfortunately with optical imaging alone, size ratios can only be determined under the unverified assumption of equal albedo across the system.

    The specific contribution of thermal mapping for a KBO system lies in the possibility to determine geometric albedos for each detected system's member, by using the radiometric method, hence allowing one to break the albedo/size degeneracy. This technique can possibly reveal a different picture of a system's physical properties than what can be determined from optical imaging alone.

    The Atacama Large Millimeter Array is the only instrument operating in the thermal regime offering sufficient spatial resolution and point source sensitivity to be able to detect and separate Kuiper-Belt multiple systems other than Pluto/Charon. We present the first spatially resolved thermal ALMA observations of three well known Kuiper Belt systems: Varda/Ilmare, Salacia/Actea and Lempo/Hiisi, which belong to different dynamical populations. Our results indicate that in two of these systems, the assumption of equal albedo across the system does not hold, resulting in a significant reassessment of size ratios.

  38. McKinnon, W., Stern, S., Spencer, J., et al., (including Grundy, W.), 2020, DPS, 52, 206.02, Evolution of Binary Planetesimals due to Gas Drag in the Protosolar Nebula
    The apparent gentle merger of the two lobes of the cold classical Kuiper belt object (KBO) 486958 Arrokoth, as revealed by New Horizons (Stern et al., Science 364, eaaw9771, 2019; Spencer et al., Science 367, aay3999, 2020; Grundy et al., Science 367, aay3705, 2020), prompts consideration of the physical mechanism(s) that might have driven mergers of originally co-orbiting binaries (which are known to be common in the Kuiper belt today). In McKinnon et al. (Science 367, aay6620, 2020 [M20]) several mechanisms were examined: tides, collisions, Kozai-Lidov cycling, asymmetric radiation effects (YORP and BYORP), and gas drag. Here we examine and update the case for gas drag, both as it might have affected Arrokoth and more generally. The evolution of binaries in a gaseous protoplanetary disk was first considered in detail by Perets & Murray-Clay (Astrophys. J. 733, 56, 2011 [PMC]), who focused on the possibility of differential wind shear causing binaries to become unbound, and secondarily on the possibility that gas drag could cause binary inspiral and merger. The former is not an issue for the relatively massive lobes of Arrokoth, and we derive a new result for the latter. Though the protosolar nebular gas at Arrokoth's distance is quite dilute and binary motions slow, it is the headwind due to pressure support of the nebula that determines the drag regime, irrespective of the binary's orientation, and couples to the slower velocity of the co-orbiting binary. As the binary pinwheels in this nebular wind, each of its lobes will alternately feel accelerating and decelerating torques; time averaged the difference does not average to zero. M20 derived a stopping time (e-folding time of the binary's angular momentum) for Arrokoth as low as 1-2 Myr, based on the classic Whipple-Weidenschilling drag formulae, recognizing that inspiral of an extended binary orbit could take longer than the nominal nebular lifetime of ~5 Myr. Using the standard drag law in PMC, and with a corrected estimate for the Reynolds number, lengthens these time scales further (and all such estimates are subject to the uncertainties in nebular and binary density). Nevertheless, we expect the importance of gas drag to increase for KBO binaries that are smaller, lower density, less inclined, and/or form closer to the Sun.
  39. Spencer, D., Ragozzine, D., Pincock, S., et al., (including Grundy, W.), 2020, DPS, 52, 206.03, Non-Keplerian Effects in Kuiper Belt Multiples
    As the number of solar system small body multiple systems (including binaries) grows in number and in observational baseline, advanced dynamical modelling will reveal physical, orbital, and spin properties that are currently poorly understood. For example, among Kuiper Belt Objects (KBOs) beyond Neptune, only a few have well determined obliquities, but observations of orbital precession due to non-spherical shapes can identify spin pole directions and obliquities. The ~50 KBO Binaries with known orbital solutions have only been studied assuming Keplerian motion, but evidence suggests that several of these are beginning to show observationally significant non-Keplerian effects. To study these effects, we have developed and validated an n-quadrupole integrator SPINNY (SPIN + N-bodY) which can include all the dominant non-Keplerian effects relevant within observational precision. SPINNY has been combined with advanced Bayesian model fitting for KBO astrometry in a new modeling tool called MultiMoon. We present MultiMoon along with some potential use cases to demonstrate its value. We also present results on an analysis of the 47171 Lempo (1996 TC36) KBO trinary system using MultiMoon.
  40. Presler-Marshall, B., Schleicher, D., Knight, M., et al., (including Devogele, M.), 2020, DPS, 52, 212.06, Diatomic Sulfur in Jupiter Family Comets
    Diatomic Sulfur in Jupiter Family Comets

    The first astronomical detection of diatomic sulfur (S2) was in comet IRAS-Araki-Alcock in 1983 using the IUE satellite (A'Hearn et al. 1983) and it has since been remotely detected in 3 other comets. All four remote S2 detections have come from objects originating from the Oort cloud, and the only detection in an object originating from the Kuiper Belt was taken in situ by the Rosetta mass spectrometer at 67P/Churyumov-Gerasimenko (Calmonte et al. 2016). As many compositional differences have been observed between Kuiper Belt and Oort Cloud objects, there is no compelling reason to assume that S2 ought to be present in similar abundances in both populations. Observations of three Jupiter Family Comets (252P/LINEAR, 45P/Honda-Mrkos-Pajdusakova and 46P/Wirtanen) were conducted using the DeVeny Spectrograph on the Lowell Discovery Telescope (formerly the Discovery Channel Telescope) between 2016 and 2018, ranging from 3000 to 4000 A. Geocentric distances were all under 0.1 AU, yielding a spatial resolution on the order of 60 km/arcsec. S2 is believed to sublimate directly from the surface of the nucleus, and the short lifetime (approximately 450 seconds) prior to photodissociation means that high spatial resolution, and thus a very low geocentric distance, is needed to search for the molecule. The observing geometry is therefore relatively rare, and another similar opportunity will not present itself for nearly another decade. Preliminary results indicate the presence of several unexplained emission features in the spectra of both 46P and 252P. Work is ongoing to ascertain whether those features match those expected by the fluorescence model (Reyle and Boice, 2003) or if another yet-unidentified molecule has been detected.

    This work is supported by NASA's Solar System Observations Program grant 80NSSC18K0856 and the Marcus Cometary Research Fund.

  41. Parker, A., Benecchi, S., Grundy, W., et al., 2020, DPS, 52, 307.01, Cold Classical Binary KBOs in the Solar System Origins Legacy Survey: Preliminary Results from Complete Survey
    The Solar System Origins Legacy Survey (SSOLS) is a Hubble Space Telescope Treasury Program targeting a very large, well-characterized sample of cold classical Kuiper Belt Objects in an effort to determine the intrinsic properties of the binary systems endemic to that population. Observations for this program were completed in July of 2020, revealing 25 clearly-resolved binary systems and 172 objects currently identified as solitary. Here we will provide an overview of SSOLS, including survey design and motivation, as well as our initial results regarding the intrinsic binary fraction of the cold classical Kuiper Belt. We confirm a very strong trend in apparent binary fraction with system brightness, but also confirm that this can largely be explained as a novel discovery bias. We show that the binary population's luminosity function is shifted to brighter values with respect to that of solitary objects. The size of this shift can be used to constrain the origin of these binary systems, and the SSOLS preliminary results suggest that this luminosity function shift is approximately 1 magnitude larger than would be expected through origin scenarios involving common formation through collapse of swarms of cm-scale particles. We will discuss this potential tension with leading theories of the origin of the cold classical KBOs, possible alternative scenarios, and our ongoing efforts to leverage the SSOLS Treasury Sample to illuminate the origin and history of the outer solar system.
  42. Benecchi, S., Parker, A., Porter, S., et al., (including Grundy, W.), 2020, DPS, 52, 307.02, Correlated Colors of Cold Classical Binary KBOs from the HST Solar System Origins Legacy Survey
    In HST Cycle 26 we successfully observed a treasury sample of 197 cold classical (CC) Kuiper Belt Objects (KBOs), The Solar System Origins Legacy Survey (SSOLS), at optical wavelengths to measure an F606W-F814W color and to look for binaries using the Wide Field Camera 3/UVIS (WFC3/UVIS). Our KBO sample draws on the highly successful, and bias-correctable, ground-based discovery surveys the Canada France Ecliptic Plane Survey (CFEPS), and the Outer Solar System Origins Survey (OSSOS) with the goal of better understanding the binarity and luminosity function of the intrinsic CC KBO population. Here we give an overview of the survey and present the resolved colors for 25 clearly resolved binary cold classical KBOs, and the colors of 172 objects identified as solitary at the limit of HST's spatial resolution. This large, high-quality sample permits robust testing of previously identified trends in colors. We find evidence supporting a trend of color with system brightness, with fainter objects in the sample being redder. Further, we find that while primaries and secondaries in binary systems have colors similar to one another, secondaries tend to be slightly redder than their primaries, and this shift is consistent with the overall trend of color with brightness in the entire CC KBO population. We will explore these trends and their implications for the origins and evolution for the CC KBO population and the outer solar system as a whole.
  43. Bair, A., Schleicher, D., Knight, M., et al., 2020, DPS, 52, 313.06, The Unusual Chemical Composition of Interstellar Comet 2I/Borisov
    Comet 2I/Borisov, discovered 2019 August 30, is the second interstellar object detected in our solar system, and the first inter-stellar object exhibiting cometary activity. Initial observations of the comet's composition proved most interesting, with clear detections of CN but comparatively extremely low abundances of C2 and low upper limits for C3. These early observations placed 2I/Borisov firmly in the carbon-chain depleted class of comets as defined by A'Hearn et al. (1995). Our updated database, which builds on the dataset from A'Hearn et al. and now includes 40 years of observations, indicates these early observations place Borisov more specifically into the strongly carbon-chain depleted (i.e. strongly depleted in both C2 and C3) compositional class. When we froze our database in 2016 (Schleicher and Bair 2016), eight of our 114 well-determined comets were grouped into this compositional class, including the prototype depleted comet 21P/Giacobini-Zinner, 73P/Schwassmann-Wachmann 3 and 43P/Wolf-Harrington, among others. Since 2016, we have determined several additional comets are carbon-chain depleted, with 48P/Johnson, 123P/West-Hartley, and 260P/McNaught falling in the strongly carbon-chain depleted class and 114P/Wiseman-Skiff borderline between the strongly and moderately carbon-chain depleted classes. Unlike the other carbon-chain depleted comets we have observed, which show no variation in composition with heliocentric distance, 2I/Borisov became far less depleted as it moved closer to the Sun, and by December exhibited only moderate carbon-chain depletion. A further indication of its unusual composition, 2I/Borisov has a higher NH/OH ratio than any of the 114 objects in our restricted database. We will compare our compositional observations of 2I/Borisov with those obtained by other researchers, and place it into the context of our database, showing that while 2I/Borisov contains the same chemical components as comets originating in our solar system, its composition and behavior with changing temperature appears to be unique. This work is supported by NASA's Solar System Observations Program grant 80NSSC18K0856.
  44. Noll, K., Brown, M., Weaver, H., et al., (including Grundy, W.), 2020, DPS, 52, 401.01, Detection of a Satellite of the Trojan Asteroid (3548) Eurybates A Lucy Mission Target
    We have identified a satellite of the Trojan asteroid (3548) Eurybates in images obtained with the Hubble Space Telescope. The satellite has been detected on four separate epochs, 12 and 14 September 2018, 03 January 2020 and 19 July 2020. The satellite was not detected in observations on 11 and 21 December 2019 and 03 August 2020 when it was presumed to be within 0.4 arcsec of Eurybates where it is too faint to be detected against the scattered light from the primary. The satellite has a brightness consistent with an effective diameter of d2 = 1.20.4 km for a body with the same albedo as Eurybates. The projected separation from Eurybates ranged from s ~ 1700-2300 km and varied in position. The detections and non-detections are consistent with a range of possible orbits. Eurybates is one of the targets of the Lucy Discovery mission and the early detection of this satellite provides an opportunity for a significant expansion of the scientific return from this encounter.
  45. Pinilla-Alonso, N., Popescu, M., Licandro, J., et al., (including Grundy, W.), 2020, DPS, 52, 401.03, The irregular limb of Manoetius South Pole and Improved Orbital Solution (extended analysis)
    In 2033, after a 12-year trip across the Solar System, NASA's Lucy mission will arrive at the Patroclus-Menoetius binary system, in Jupiter's L5 cloud. On its way, Lucy will visit one asteroid and seven Jupiter Trojans, all of them primitive asteroids. Lucy's foreseen discoveries about the surface geology, color, and composition of these Trojans, about their interior and bulk properties, and about the presence of satellites or rings, which have the potential of revolutionizing the knowledge of the Solar System and opening new insights into the origins of our Earth. In preparation for that moment, ground-based observations are fundamental to obtain important physical information on these targets, which is needed to plan the operations and the best observational strategy. Furthermore, they provide ground truth of the state-of-the-art analysis techniques used for the study of the whole population, which is essential to better understand the big picture.

    In this work, we present surprising results from a set of 14 lightcurves of 11 mutual events of the Patroclus-Menoetius system obtained during the last season, in 2017-2018. Results based on the first set of seven light curves (corresponding to five different events) has been recently published (Pinilla-Alonso et al. 2020, PSJ, in press) reporting the imprint for a possible crater in the south pole of Menoetius, as deep as a fourth of its radius, and an improved orbit solution for the system. This new analysis, including seven inferior events and seven superior events, provides new details of the shape of both components and a new orbit solution, which is key for the planning of the flyby of the Patroclus and Menoetius system. Figure 1: Artistic representation of the Patroclus-Menoetius system showing a void in the southern limb of Menoetius. The profile of this void was extracted from the analysis of the light curve of an occultation obtained at the Gran Telescopio Canarias (GTC) on December 08, 2017.

  46. Chandler, C., Kueny, J., Trujillo, C., et al., 2020, DPS, 52, 404.02, Cometary Activity Discovered on Centaur 2014 OG392
    We report the discovery of activity emanating from Centaur 2014 OG392. Centaurs orbit between Jupiter and Neptune, thus they are both faint and cold; 2014 OG392 orbits between 10-15 au where its equilibrium temperature would be around 60 K. Active Centaurs are poorly understood in large part because fewer than 20 have been discovered to date. We initially found suspected activity via a database search algorithm we developed to locate images of 2014 OG392 in the archival images from the Cerro Tololo Inter-American Observatory Blanco 4 m telescope Dark Energy Camera (DECam). We carried out a follow-up observing campaign with the DECam, the Las Campanas Observatory 6.5 m Walter Baade Telescope, and the 4.3 m Lowell Discovery Telescope.

    We developed a novel technique which combines observational measurements (e.g., color, dust mass) and modeling efforts (e.g., volatile sublimation, orbital dynamics) to ascertain the species most likely responsible for observed activity. For 2014 OG392 these molecules are CO2 and/or NH3; both ices are optically neutral, yet we found 2014 OG392 to be roughly one magnitude redder than the Sun in B-R, so the reddening agent is as yet unknown.

    This material is based upon work supported by the NSF Graduate Research Fellowship Program under grant No. 2018258765 to COC.

  47. Engle, A., Hanley, J., Thompson, G., et al., (including Grundy, W.), 2020, DPS, 52, 408.02, Phase Diagram for the Methane-Ethane System at Conditions Relevant to Titan
    On Titan, methane (CH4) and ethane (C2H6) are the dominant species found in the polar lakes and seas. In this study, we have combined molecular dynamics simulations with laboratory work to both create a binary phase diagram at cryogenic temperatures and gain a better understanding of how the system interacts at a molecular level.

    The molecular dynamics (MD) simulations reveal that the methane-ethane system deviates from ideality as the mixing ratio approaches the eutectic point, indicating that the methane-ethane interactions are stronger than the self-interactions of either molecule at the eutectic. Identifying the deviation from ideality was accomplished through comparing the MD simulations to experimental data, focusing on excess volume, density, and temperature vs. mixing ratio of the liquidus line and eutectic point.

    From the laboratory work, we have found that Raman spectroscopy is a reliable means of detecting the liquidus, solidus, and solvus lines, allowing for full characterization of the phase diagram. The liquidus is defined as the first point in which ice forms on cooling or when the last ice disappears on warming. The solidus marks the last point in which liquid occurs on cooling the sample. Lastly, the solvus differentiates between a fully homogeneous system and a structure where one species dominates the crystal structure, with the other as only a minority contaminant.

    The temperatures and mixing ratios at which the solidus and solvus lines occur are mostly below 90 K. This means they likely have a larger impact on processes taking place at deeper parts of the lakes and seas as well as for portions of the atmosphere, as opposed to on the surface. In general, this diagram is not only useful in terms of understanding the methane-ethane system itself, but also as a foundation for creating more complex systems that better exemplify the compositions of Titan's various lakes and seas.

  48. Hanley, J., Wing, B., Engle, A., et al., (including Grundy, W.), 2020, DPS, 52, 408.06, The Effects of Propane on the Liquids of Titan
    The lakes and seas of Titan are composed primarily of methane (CH4) and ethane (C2H6), with the concentration of dissolved nitrogen (N2) depending on the ratio of methane to ethane, the temperature, and pressure. Propane (C3H8) is formed photochemically in the upper atmosphere of Titan, and condenses at the tropopause. The freezing point of pure propane is 85.5 K, meaning that it would be liquid on the surface of Titan, like methane and ethane. We have begun an exploration of the effect of propane on methane, ethane, nitrogen, and their mixtures in the NAU Astrophysical Materials Laboratory. Cryogenic samples are studied via Raman spectroscopy and photography. As nitrogen was added to a binary hydrocarbon mixture of either propane-methane or propane-ethane, it caused the formation of a second liquid. The droplets form at the meniscus and this nitrogen-rich denser liquid falls once enough material has collected to break surface tension. Ice can form under certain conditions. Differences in behavior of the propane-ethane system and the propane-methane system can be attributed to the difference in nitrogen solubility. For further analysis, the phase diagrams at conditions where the second liquids were observed were calculated using CRYOCHEM. We also modeled a homogeneous N2:CH4:C2H6:C3H8 liquid system to understand the breakdown of ideality. In these simulations, real effects are quantified by calculating the binding free energy between each pair of molecules. We found that increasing alkane length results in a decrease in binding strength between N2 and each of the alkanes, which suggests a molecular explanation for the phase behavior observed in the experiments of these systems at lower temperatures. In summary, pure propane should not freeze on the surface of Titan. However, we see propane ice form under certain conditions that might be possible on Titan. We also see that the liquid-liquid system can form with the addition of propane. We continue to explore the effects of propane on methane, ethane and nitrogen, both individually and additively, and constrain the conditions under which interesting phenomena occur.
  49. Gustafsson, A., Moskovitz, N., 2020, DPS, 52, 409.01, Revealing Regolith Properties of Near-Earth Asteroids
    The most common method for estimating surface grain size of asteroids is by determining thermal inertia using thermophysical models. Calculating accurate values of thermal inertia is a difficult process requiring a shape model, thermal-infrared observations obtained over broad viewing geometry, and detailed thermophysical modeling. Nevertheless, thermal inertia is a sensitive probe of surface regolith properties (Christensen et al. 2003), and therefore is of great importance in the design of instrumentation and observing strategies for asteroid missions where knowledge of surface characteristics is critical. Yet, thermal inertia alone cannot uniquely describe the full complexity of asteroid surface properties. This was true for OSIRIS-REx target (101955) Bennu whose thermally derived grain size estimates did not accurately represent the rough, bouldered surface observed by the spacecraft (Dellagiustina et al. 2019).

    Radiative transfer models are some of the most widely used tools for compositional analyses of planetary bodies and have the opportunity to provide a comprehensive understanding of asteroid surface properties when used in conjunction with thermal modeling. In application to silicate-rich asteroids, radiative transfer models have almost exclusively been used to derive olivine to pyroxene abundance ratios. However, new formulas have been developed for deriving mineralogy from visible and near-infrared spectra that display prominent olivine and pyroxene (1 and 2 micron) absorption bands (e.g. Burbine et al. 2007, Reddy et al. 2011). Furthermore, the effects of non-compositional parameters (temperature, phase angle, grain size) have been well characterized, allowing for a more detailed analysis of these parameters with radiative transfer models.

    We present a new implementation of the Hapke radiative transfer model to constrain grain size for unresolved asteroid surfaces. This technique can be applied to a large number of targets including near-Earth and Main Belt asteroids. This model is optimized for investigating S/Q type asteroids whose spectra are dominated by olivine and pyroxene absorption bands. Results from this study compliment thermal grain size estimates, when they exist, and provide standalone constraints on surface properties for a much larger number of near-Earth and Main Belt asteroids.

    We will present a validation of the model against ordinary chondrite meteorites and well-studied near-Earth asteroids (e.g. Eros, Itokawa) with thermal inertia and spacecraft observations.

    This work is supported by the NASA NEOO program, grant number NNX17AH06G.

  50. Navarro-Meza, S., Trilling, D., Mommert, M., et al., 2020, DPS, 52, 409.05D, Taxonomy of sub-kilometer NEOs with Machine Learning and Photometry
    As part of our multi-observatory, multi-filter campaign, we present results from observations of 237 near-Earth Objects (NEOs) obtained with the RATIR instrument on the 1.5 m robotic telescope at the San Pedro Martir's National Observatory in Mexico. Our project is focused on rapid response photometric observations of NEOs with absolute magnitudes in the range 20-25. Our data with coverage in the near infrared and optical range was analyzed with Machine Learning techniques, while optical-only data was analyzed via Monte Carlo simulations. Our method allows us to obtain taxonomic classification of sub-kilometer objects using photometry and small telescopes, representing a convenient characterization strategy.
  51. Kueny, J., Chandler, C., Devogele, M., et al., (including Moskovitz, N.), 2020, DPS, 52, 415.02, Shape Model, Pole Solution Implications, and Refined Rotational Period of (155140) 2005 UD
    (155140) 2005 UD is a Near-Earth Asteroid in a companion orbit with (3200) Phaethon, an active asteroid in a highly-elliptical orbit thought to be responsible for the Geminid meteor shower. Evidence points to a genetic relationship between these two objects (Devogele et al. 2020), but we have yet to fully understand how 2005 UD and Phaethon could have separated into this associated pair. Notably, 2005 UD is the extended mission target for the Japanese Aerospace Exploration Agency DESTINY+ mission scheduled to launch in 2024. Presented herein are new observations of 2005 UD using the Lowell Discovery Telescope, Nordic Optical Telescope, and TRAPPIST-North motivated by access to a previously unseen viewing geometry in October-November 2019. Lightcurve inversion using our new data, archival lightcurve data from an advantageous apparition in late 2018, and data from an epoch in late 2005 were used to derive a shape model of 2005 UD. Results pertaining to 2005 UD's mass loss from additional analyses involving these new data will also be discussed. We also determined a retrograde spin state, largely consistent with a previous thermophysical analysis, and a refined sidereal rotational period of Psid = 5.2338 0.0040 hours. Although a precise shape model is at present infeasible due to remaining gaps in lightcurve data at critical viewing aspects, we were able to leverage our results to help limit the range of formation scenarios and the link to Phaethon in the context of non-gravitational forces and timescales associated with the physical evolution of the system.
  52. Fedorets, G., Micheli, M., Jedicke, R., et al., (including Moskovitz, N., Devogele, M.), 2020, DPS, 52, 415.03, Characterization of 2020 CD3, Earth's Second Minimoon
    Introduction: Small NEOs may become captured temporarily by planets. Theoretical models (Granvik et al. 2012, Fedorets et al. 2017) predict the existence of a steady-state population of these so-called minimoons also in the Earth-Moon system. Only one minimoon, 2006 RH120 has been discovered until recently (Kwiatkowski et al. 2009). Minimoons have been identified as viable targets for in situ exploration of metre-sized asteroids, as test cases for initial steps of asteroid resource utilisation (Granvik et al. 2013, Jedicke et al. 2018), and as constraints for the size-frequency distribution of metre-sized NEOs (Harris & D'Abramo 2015, Granvik et al. 2016, Tricarico 2017, Brown et al. 2002). So far, the observational evidence of the minimoon population has been lacking.

    Observations: The object 2020 CD3 was discovered on February 15th 2020 at the Mt. Lemmon station of the Catalina Sky Survey, and was reported to be on a geocentric orbit the following night. We report the results of the astrometric and photometric observational campaign of 2020 CD3 performed by Gemini North, LDT, NOT, CFHT, CSS, and other telescopes during spring 2020. By investigating the solar radiation pressure signature on the astrometry of 2020 CD3, and broad-band photometry, we present evidence that it is the second temporary natural satellite in the Earth-Moon system. We describe its discovery circumstances, physical characterisation, rotational period, orbital evolution, and possible origin.

    Discussion: We discuss the challenges of discovering minimoons with contemporary surveys. For the first time, we are able to compare the observational evidence of minimoons with the theoretical models. We assess the capture duration and rotation period of 2020 CD3 in context of simulation and similar objects.

    Prospects: The discovery of 2020 CD3, and the comparison to discovery predictions with other surveys (Bolin et al. 2014), assures that the expectation of discovery of tens of minimoons with LSST is realistic (Fedorets et al. 2020). With the anticipated growth of the population of minimoons, the path for further exploration of minimoons is foreseen.

    1: Bolin et al. (2014), Icarus 241, 280 ; 2: Brown et al. (2002), Nature, 420, 294 ; 3: Fedorets et al. (2017) Icarus, 285, 83 ; 4: Fedorets et al. (2020), Icarus, 338, 113517 ; 5: Granvik et al. (2012), Icarus, 218, 262 ; 6: Granvik et al. (2013) in V. Badescu ed. Asteroids: Prospective Energy and Material Resources, 151 ; 7: Granvik et al. (2016), Nature, 530, 303 ; 8: Harris & D'Abramo (2015), Icarus, 257, 302 ; 9: Jedicke et al. (2018) FrASS, 5, A13 ; 10: Kwiatkowski et al. (2009), A&A, 495, 967 ; 11: Tricarico et al. (2017), Icarus, 284, 416

  53. Devogele, M., Virkki, A., Marshall, S., et al., (including Moskovitz, N., Skiff, B.), 2020, DPS, 52, 415.04, Heterogeneous surface of 1998 OR2
    We report observations of the H=15.8 mag potentially hazardous asteroid 52768 (1998 OR2) obtained during its 2020 apparition. On April 29th 2020, OR2 experienced its closest approach to Earth (16.4 Lunar distance) until 2079. Observations were obtained in polarimetry with the Torino Polarimeter at the Calern observatory (France; MPC 010) in February and April 2020, in radar with the Arecibo Radio telescope (Puerto Rico; MPC 251) Planetary Radar system from April 13th to 23rd 2020, and in photometry with the TRAPPIST-North and the Las Cumbres observatory (LCOGT) network of telescopes. One epoch was obtained by the NEOWISE mission.

    Using the polarimetric albedo-polarization relation [1] we derived a visual albedo pV = 0.16 0.02 corresponding to an equivalent diameter of D=2.3 km based on its measured H=15.8 absolute magnitude. The NEOWISE observation provides other determinations of D=2.5 0.5 km and pV = 0.13 0.04 consistent with the polarimetric data. Radar delay-Doppler images, with a resolution of 7.5 m per pixel in delay and 0.037 Hz in frequency, provide another independent size measurement and display a maximum extent of 2.16 km 0.05 km. Both radar and optical lightcurve observations confirm the rotation period of p=4.112 h [2], with a low amplitude lightcurve varying from single to double peaked, based on the phase angle and aspect angle variation throughout the apparition.

    The polarimetric observations were conducted over more than one rotation period during each night and we observe a consistent phase-locked variation of the polarization. Asteroid polarization is independent of shape and is at first order dependent on the surface albedo. The observed variation of the polarization thus suggests that the surface of OR2 is heterogeneous. Such variation has only previously been observed for 4 Vesta [3], 1943 Anteros [4], and 3200 Phaethon [5,6].

    The radar images of OR2 suggest the presence of a large concavity or crater near the radar sub-latitude (closest point of the object to the observer). Phasing the radar and polarimetric observations, we find that the maximum of polarization occurs when the radar concavity is directly facing the observer. Such correlation suggests that the polarimetric variations could be related to the presence of the concavity and that it possesses lower albedo or different scattering properties than the rest of the surface.

    1: Cellino et al., 2015 MNRAS, 451, 3473 ; 2: Skiff et al, 2019, MPB, 46 ; 3: Cellino et al., 2016, MNRAS, 456, 248 ; 4: Masiero et al., 2010, Icarus, 207, 795 ; 5: Devogele et al., 2018 MNRAS, 465, 4335 ; 6: Borisov et al., 2018 MNRAS, 480, L131

  54. Keane, J., Porter, S., Beyer, R., et al., (including Grundy, W.), 2020, DPS, 52, 508.02, Geophysics of (486958) Arrokoth revealed by New Horizons
    On 1 January 2019, NASA's New Horizons spacecraft performed the first flyby of a small Kuiper Belt Object: (486958) Arrokoth (formerly 2014 MU69). This ~35-km long, bilobed contact binary is a member of the cold classical Kuiper belt populationa dynamically stable reservoir of small bodies that has remained relatively untouched since the earliest epochs of solar system formation. In short, Arrokoth is a relic planetesimala leftover building block of planet formationand by studying its geology and geophysics we can explore the processes and environment that built our solar system. In this work, we present the current state of knowledge of Arrokoth's shape and geophysical environment, and quantitative comparisons to other small bodies across the solar system. Arrokoth's flattened, bilobate nature yields an unintuitive physical environment, making geophysical analyses critical to interpreting the observed geology. Several surface features correlate with the modeled geophysical environment. Most notably, bright surface features appear preferentially in geopotential lowslike Arrokoth's neck and the bright annulus on the encounter hemisphere of the large lobeperhaps indicative of mass-wasting or other geologic processes. While New Horizons was not able to directly measure Arrokoth's mass, several lines of evidence suggest that it has a very low bulk density. The statistics of surface slopes, required neck strength, and overall configuration of the contact binary suggest a bulk density between 200-500 kg/m3. While this density is low compared to characterized (i.e., larger) Kuiper Belt objects and many comets (e.g., 67P/Churyumov-Gerasimenko density = 532 kg/m3), it is suspiciously similar to some small ring moons of Saturn (e.g., Atlas, Pan, Methone have densities between 300-400 kg/m3). While not conclusive, this supports the hypothesis that Arrokoth formed in a gentle environment (e.g., Stern et al. 2019, Spencer et al. 2020, McKinnon et al. 2020).
  55. Bertrand, T., Forget, F., Schmitt, B., et al., (including Grundy, W.), 2020, NatCo, 11, 5056, Equatorial mountains on Pluto are covered by methane frosts resulting from a unique atmospheric process
    Pluto is covered by numerous deposits of methane, either diluted in nitrogen or as methane-rich ice. Within the dark equatorial region of Cthulhu, bright frost containing methane is observed coating crater rims and walls as well as mountain tops, providing spectacular resemblance to terrestrial snow-capped mountain chains. However, the origin of these deposits remained enigmatic. Here we report that they are composed of methane-rich ice. We use high-resolution numerical simulations of Pluto's climate to show that the processes forming them are likely to be completely different to those forming high-altitude snowpack on Earth. The methane deposits may not result from adiabatic cooling in upwardly moving air like on our planet, but from a circulation-induced enrichment of gaseous methane a few kilometres above Pluto's plains that favours methane condensation at mountain summits. This process could have shaped other methane reservoirs on Pluto and help explain the appearance of the bladed terrain of Tartarus Dorsa.
  56. Dorn-Wallenstein, T., Levesque, E., Neugent, K., et al., 2020, ApJ, 902, 24, Short-term Variability of Evolved Massive Stars with TESS. II. A New Class of Cool, Pulsating Supergiants
    Massive stars briefly pass through the yellow supergiant (YSG) phase as they evolve redward across the H-R diagram and expand into red supergiants (RSGs). Higher-mass stars pass through the YSG phase again as they evolve blueward after experiencing significant RSG mass loss. These post-RSG objects offer us a tantalizing glimpse into which stars end their lives as RSGs and why. One telltale sign of a post-RSG object may be an instability to pulsations, depending on the star's interior structure. Here we report the discovery of five YSGs with pulsation periods faster than 1 day, found in a sample of 76 cool supergiants observed by the Transiting Exoplanet Survey Satellite at a two-minute cadence. These pulsating YSGs are concentrated in an H-R diagram region not previously associated with pulsations; we conclude that this is a genuine new class of pulsating star, fast yellow pulsating supergiants (FYPSs). For each FYPS, we extract frequencies via iterative prewhitening and conduct a time-frequency analysis. One FYPS has an extracted frequency that is split into a triplet, and the amplitude of that peak is modulated on the same timescale as the frequency spacing of the triplet; neither rotation nor binary effects are likely culprits. We discuss the evolutionary status of FYPS and conclude that they are candidate post-RSGs. All stars in our sample also show the same stochastic low-frequency variability found in hot OB stars and attributed to internal gravity waves. Finally, we find four Cygni variables in our sample, of which three are newly discovered.
  57. Rector, T., Prato, L., Strom, A., 2020, AJ, 160, 189, Herbig-Haro Outflows in Circinus W
    We report the discovery of new Herbig-Haro (HH) outflows in the Western Circinus molecular cloud. They were found using a color-composite imaging method that reveals faint H emission in complex environments. Follow-up observations in [S II] confirmed their classification as HH objects. Nearly half of the newly discovered objects are part of the HH 76 outflow and are associated with a likely young stellar object (YSO) candidate. We also identify the source of a second outflow. Three newly discovered objects are part of a third outflow whose origin is unknown. Four more HH objects are also discovered, each of which has a location and morphology that does not suggest an origin. In total there must be at least five YSOs in the field currently producing outflows. The discovery of new HH objects and associated driving sources in this cloud complex provides more evidence for active star formation and a relatively young age in this seldom-studied region.
  58. Eckert, K., Bernstein, G., Amara, A., et al., (including Kuehn, K.), 2020, MNRAS, 497, 2529, Noise from undetected sources in Dark Energy Survey images
    For ground-based optical imaging with current CCD technology, the Poisson fluctuations in source and sky background photon arrivals dominate the noise budget and are readily estimated. Another component of noise, however, is the signal from the undetected population of stars and galaxies. Using injection of artifical galaxies into images, we demonstrate that the measured variance of galaxy moments (used for weak gravitational lensing measurements) in Dark Energy Survey (DES) images is significantly in excess of the Poisson predictions, by up to 30 per cent, and that the background sky levels are overestimated by current software. By cross-correlating distinct images of 'empty' sky regions, we establish that there is a significant image noise contribution from undetected static sources (US), which, on average, are mildly resolved at DES resolution. Treating these US as a stationary noise source, we compute a correction to the moment covariance matrix expected from Poisson noise. The corrected covariance matrix matches the moment variances measured on the injected DES images to within 5 per cent. Thus, we have an empirical method to statistically account for US in weak lensing measurements, rather than requiring extremely deep sky simulations. We also find that local sky determinations can remove most of the bias in flux measurements, at a small penalty in additional, but quantifiable, noise.
  59. Zhang, H., Smith, R., Oh, S., et al., (including Hunter, D.), 2020, ApJ, 900, 152, The Blue Compact Dwarf Galaxy VCC 848 Formed by Dwarf-Dwarf Merging: H I Gas, Star Formation, and Numerical Simulations
    A clear link between a dwarf-dwarf merger event and enhanced star formation (SF) in the recent past was recently identified in the gas-dominated merger remnant VCC 848, offering by far the clearest view of a gas-rich late-stage dwarf-dwarf merger. We present a joint analysis of JVLA H I emission line mapping, optical imaging, and numerical simulations of VCC 848 in order to examine the effect of the merger on the stellar and gaseous distributions. VCC 848 has less than 30% of its H I gas concentrated within the central high-surface-brightness star-forming region, while the remaining H I is entrained in outlying tidal features. Particularly, a well-defined tidal arm reaches N(H I) comparable to the galaxy center but lacks SF. The molecular gas mass inferred from the current SF rate (SFR) dominates over the atomic gas mass in the central 1.5 kpc. VCC 848 is consistent with being a main-sequence star-forming galaxy for its current stellar mass and SFR. The H II region luminosity distribution largely agrees with that of normal dwarf irregulars with similar luminosities, except that the brightest H II region is extraordinarily luminous. Our N-body/hydrodynamical simulations imply that VCC 848 is a merger between a gas-dominated primary progenitor and a gas-bearing star-dominated secondary. The progenitors had their first passage on a near-radial noncoplanar orbit more than 1 Gyr ago. The merger did not build up a core as compact as typical compact dwarfs with a centralized starburst, which may be partly ascribed to the star-dominated nature of the secondary and, in a general sense, a negative stellar feedback following intense starbursts triggered at early stages of the merger.
  60. Morgan, R., Soares-Santos, M., Annis, J., et al., (including Kuehn, K.), 2020, ApJ, 901, 83, Constraints on the Physical Properties of GW190814 through Simulations Based on DECam Follow-up Observations by the Dark Energy Survey
    On 2019 August 14, the LIGO and Virgo Collaborations detected gravitational waves from a black hole and a 2.6 solar mass compact object, possibly the first neutron star-black hole merger. In search of an optical counterpart, the Dark Energy Survey (DES) obtained deep imaging of the entire 90% confidence level localization area with Blanco/DECam 0, 1, 2, 3, 6, and 16 nights after the merger. Objects with varying brightness were detected by the DES Pipeline, and we systematically reduced the candidate counterparts through catalog matching, light-curve properties, host-galaxy photometric redshifts, Southern Astrophysical Research spectroscopic follow-up observations, and machine-learning-based photometric classification. All candidates were rejected as counterparts to the merger. To quantify the sensitivity of our search, we applied our selection criteria to full light-curve simulations of supernovae and kilonovae as they would appear in the DECam observations. Because the source class of the merger was uncertain, we utilized an agnostic, three-component kilonova model based on tidally disrupted neutron star (NS) ejecta properties to quantify our detection efficiency of a counterpart if the merger included an NS. We find that, if a kilonova occurred during this merger, configurations where the ejected matter is greater than 0.07 solar masses, has lanthanide abundance less than 10-8.56, and has a velocity between 0.18c and 0.21c are disfavored at the 2 level. Furthermore, we estimate that our background reduction methods are capable of associating gravitational wave signals with a detected electromagnetic counterpart at the 4 level in 95% of future follow-up observations.
  61. Steckloff, J., Soderblom, J., Farnsworth, K., et al., (including Hanley, J., Grundy, W.), 2020, PSJ, 1, 26, Stratification Dynamics of Titan's Lakes via Methane Evaporation
    Saturn's moon Titan is the only extraterrestrial body known to host stable lakes and a hydrological cycle. Titan's lakes predominantly contain liquid methane, ethane, and nitrogen, with methane evaporation driving its hydrological cycle. Molecular interactions between these three species lead to nonideal behavior that causes Titan's lakes to behave differently than Earth's lakes. Here, we numerically investigate how methane evaporation and nonideal interactions affect the physical properties, structure, dynamics, and evolution of shallow lakes on Titan. We find that, under certain temperature regimes, methane-rich mixtures are denser than relatively ethane-rich mixtures. This allows methane evaporation to stratify Titan's lakes into ethane-rich upper layers and methane-rich lower layers, separated by a strong compositional gradient. At temperatures above 86 K, lakes remain well mixed and unstratified. Between 84 and 86 K, lakes can stratify episodically. Below 84 K, lakes permanently stratify and develop very methane-depleted epilimnia. Despite small seasonal and diurnal deviations (<5 K) from typical surface temperatures, Titan's rain-filled ephemeral lakes and "phantom lakes" may nevertheless experience significantly larger temperature fluctuations, resulting in polymictic or even meromictic stratification, which may trigger ethane ice precipitation.
  62. Buchanan, L., Schwamb, M., Fraser, W., et al., (including Thirouin, A.), 2020, EPSC, EPSC2020-185, Col-OSSOS: Probing Ice Line/Colour Transitions within the Kuiper Belt's Progenitor Populations
    The Colours of the Outer Solar System Origins Survey (Col-OSSOS, Schwamb et al., 2019) has examined the surface compositions of Kuiper Belt Objects (KBOs) by way of broadband g-, r- and J-band photometry, using the Gemini North Hawaii Telescope. This survey showed a bimodal distribution in the colours of the objects surveyed, consistent with previous colour surveys (Tegler et al., 2016). These broadband surface colours can be considered a proxy for surface composition of these KBOs, so this survey allows the frequency of different surface compositions within the outer Solar System to be explored. The bimodality of the observed colours suggests the presence of some sort of surface transition within the Kuiper belt, perhaps due to a volatile ice-line transition in the pristine planetesimal disk that existed before Neptune"s migration. The Outer Solar System Origins Survey (OSSOS, Bannister et al., 2018), from which Col-OSSOS selected objects brighter than 23.6 r-band magnitude, has well characterised and quantified biases, so allowing for comparisons between the observations and numerical models of the Kuiper belt.By applying different colour transitions to the primordial planetesimal disk, in this work we explore the possible positions for ice line/colour transitions within the planetesimal disk that existed before Neptune"s migration. Within Schwamb et al. (2019), a simplified toy model was used to investigate the possible position of this transition. Nesvorny et al. (2020) has investigated the primordial colour fraction, in particular how it can create the inclination distribution that we see in the colours of KBOs today. In this work we use a full dynamical model of the Kuiper belt to more precisely pinpoint the possible location of this transition. We make use of the model by Nesvorny & Vokrouhlicky (2016) of Neptune"s migration from 23 au to 30 au, and the consequent perturbation of the Kuiper belt into its current form. This model allows precise tracking of the objects from their pre-Neptune migration to post-Neptune migration positions, allowing various colour transition positions in the initial disk, an example of which is shown in Figure 1, to be compared with the Col-OSSOS observations of the modern day disk.Figure 1: An example red/neutral transition at 27 au. The left plots show the objects in the primordial disk, while the right plots show the objects post-Neptune migration from the model of Nesvorny & Vokrouhlicky (2016).The OSSOS survey simulator (Lawler et al., 2018) can then be used to calculate which of the simulated objects could have been observed by OSSOS, and so selected by Col-OSSOS for surface colour observations. The colour transition within the initial disk, shown in Figure 1, is moved radially outwards through the disk and the corresponding outputs are compared with the Col-OSSOS colour observations to see which initial disk colour transition positions are consistent with the modern day Kuiper belt. We will present results combing an accurate dynamical model of the Kuiper Belt"s evolution by Nesvorny & Vokrouhlicky (2016) with Col-OSSOS photometry. We will explore multiple radial colour distributions in the primordial planetesimal disk and implications for the the positions of ice line/colour transitions within the Kuiper Belt"s progenitor populations. ReferencesBannister, M. T., Gladman, B. J., Kavelaars, J. J., et al. 2018, ApJS, 236, 18Lawler, S. M., Kavelaars, J. J., Alexandersen, M., et al. 2018, Front. Astron. Space Sci., 5, 14Nesvorny, D., Vokrouhlicky, D., Alexandersen, M., et al. 2020, AJ, in pressNesvorny, D., & Vokrouhlicky, D. 2016, ApJ, 825Schwamb, M. E., Bannister, M. T., Marsset, M., et al. 2019, ApJS, 243, 12Tegler, S. C., Romanishin, W., Consolmagno, G. J., & J., S. 2016, AJ, 152, 210
  63. Fedorets, G., Micheli, M., Jedicke, R., et al., (including Moskovitz, N., Devogele, M.), 2020, EPSC, EPSC2020-658, Characterisation of 2020 CD3, Earth's second minimoon
    IntroductionSmall solar system objects may occasionally become captured temporarily by planets. Theoretical models (Granvik et al. 2012, Fedorets et al. 2017) predict the existence of a steady-state population of these objects, also known as minimoons, also in the Earth-Moon system. Only one minimoon, 2006 RH120 has been discovered until recently (Kwiatkowski et al. 2009). Since minimoons spend a significant amount of time in Earth"s vicinity, they have been identified as outstanding targets for in situ exploration, or test cases for initial steps of asteroid resource utilisation (Granvik et al. 2013, Chyba et al. 2014, Brelsford et al. 2016, Jedicke et al. 2018). Moreover, not only are minimoons outstanding targets to constrain the size-frequency distribution of metre-sized asteroids (Harris & D"Abramo 2015, Granvik et al. 2016, Tricarico 2017, Brown et al. 2002), but also for studying the structure of the smallest asteroids. However, until now, the observational evidence of the minimoon population has been lacking.ObservationsThe object 2020 CD3 was discovered on February 15th 2020 at the Mt. Lemmon station of the Catalina Sky Survey, and was noticed to be on a geocentric orbit the following night. We report the results of the astrometric and photometric observational campaign to characterise 2020 CD3 performed by Gemini North, LDT, NOT, CFHT, CSS, and other telescopes during spring 2020. By investigating the solar radiation pressure signature on the astrometry of 2020 CD3, and broad-band photometry, we present evidence that 2020 CD3 is indeed the second temporary natural satellite in the Earth-Moon system. We describe its discovery circumstances, physical characterisation, rotational period and orbital evolution.DiscussionUsing 2020 CD3 as an example case, we discuss the challenges of discovering minimoons with contemporary surveys. For the first time, we are able to compare the observational evidence of minimoons with the theoretical models. We also assess the capture duration and rotation period of 2020 CD3 in context of simulation and similar objects. Finally, we compare the origin of minimoons as captured objects from the NEO population against their origin as lunar ejecta, and show why the first mechanism is dominant.ProspectsThe discovery of 2020 CD3, and the comparison to discovery predictions with other surveys (Bolin et al. 2014), assures that the expectation of discovery of tens of minimoons with LSST is realistic (Fedorets et al. 2020). With the anticipated growth of the population of minimoons, the path for further exploration of minimoons is foreseen.ReferencesBolin et al. (2014), Icarus 241, 280Brelsford et al. (2016), PSS, 123, 4.Brown et al. (2002), Nature, 420, 294.Chyba et al. (2014) JIMO, 10(2), 477.Fedorets et al. (2017) Icarus, 285, 83.Fedorets et al. (2020), Icarus, 338, 113517.Granvik et al. (2012), Icarus, 218, 262.Granvik et al. (2013) in V. Badescu ed. Asteroids: Prospective Energy and Material Resources, 151.Granvik et al. (2016), Nature, 530, 303.Harris & D"Abramo (2015), Icarus, 257, 302.Jedicke et al. (2018) FrASS, 5, A13.Kwiatkowski et al. (2009), A&A, 495, 967.Tricarico et al. (2017), Icarus, 284, 416.
  64. Leiva, R., Buie, M., Keller, J., et al., (including Wasserman, L.), 2020, PSJ, 1, 48, Stellar Occultation by the Resonant Trans-Neptunian Object (523764) 2014 WC510 Reveals a Close Binary TNO
    We report on the stellar occultation by (523764) 2014 WC510 observed on 2018 December 1 UT. This occultation campaign was part of the Research and Education Collaborative Occultation Network (RECON), a network of small telescopes spread over 2000 km in western USA and Canada. Light curves from six stations revealed three groups of two or more consecutive flux drops correlated in time between adjacent stations. A Bayesian model comparison reveals that a model with a double object occulting a double star is favored over alternative models considered. For the statistically favored model, we determined that the primary component of the object has a diameter dp = 181 16 km and the secondary ds = 138 32 km, assuming identical geometric albedo between the two components. The two components have a projected separation of 349 26 km. Adopting an absolute magnitude for the system of HV = 7.2 from the Minor Planet Center, we derive a geometric albedo of pV = 5.1% 1.7%. This is the smallest resonant object with an occultation size measurement and with a detected secondary from a ground-based stellar occultation, filling a region of the size versus separation parameter space of binary objects that is largely unexplored. The results show the capabilities of the unique design of the RECON experiment sensitive to small objects and close binaries. 2014 WC510 is presently at a low galactic latitude where the high surface density of stars will provide good occultation opportunities in the upcoming years.
  65. Dunham, T., 2020, BAAS, 52, 0317, Obituary: James L. Elliot (1943-2011)
    Jim Elliot performed numerous groundbreaking occultation studies, including the first occultation observations with the Kuiper Airborne Observatory and the discovery of Uranus' rings.
  66. Neugent, K., Levesque, E., Massey, P., et al., 2020, ApJ, 900, 118, The Red Supergiant Binary Fraction of the Large Magellanic Cloud
    The binary fraction of unevolved massive stars is thought to be 70%-100% but there are few observational constraints on the binary fraction of the evolved version of a subset of these stars, the red supergiants (RSGs). Here we identify a complete sample of RSGs in the Large Magellanic Cloud (LMC) using new spectroscopic observations and archival UV, IR, and broadband optical photometry. We find 4090 RSGs with $\mathrm{log}L/{L}_{\odot }\gt 3.5$ , with 1820 of them having $\mathrm{log}L/{L}_{\odot }\gt 4$ , which we believe is our completeness limit. We additionally spectroscopically confirmed 38 new RSG + B-star binaries in the LMC, bringing the total known up to 55. We then estimated the binary fraction using a k-nearest neighbors algorithm that classifies stars as single or binary based on photometry with a spectroscopic sample as a training set. We take into account observational biases such as line-of-sight stars and binaries in eclipse while also calculating model-dependent corrections for RSGs with companions that our observations were not designed to detect. Based on our data, we find an initial result of ${13.5}_{-6.67}^{+7.56} \% $ for RSGs with O- or B-type companions. Using the Binary Population and Spectral Synthesis models to correct for unobserved systems, this corresponds to a total RSG binary fraction of ${19.5}_{-6.7}^{+7.6} \% $ . This number is in broad agreement with what we would expect given an initial OB binary distribution of 70%, a predicted merger fraction of 20%-30%, and a binary interaction fraction of 40%-50%.
  67. Palmese, A., deVicente, J., Pereira, M., et al., (including Kuehn, K.), 2020, ApJL, 900, L33, A Statistical Standard Siren Measurement of the Hubble Constant from the LIGO/Virgo Gravitational Wave Compact Object Merger GW190814 and Dark Energy Survey Galaxies
    We present a measurement of the Hubble constant H0 using the gravitational wave (GW) event GW190814, which resulted from the coalescence of a 23 M black hole with a 2.6 M compact object, as a standard siren. No compelling electromagnetic counterpart has been identified for this event; thus our analysis accounts for thousands of potential host galaxies within a statistical framework. The redshift information is obtained from the photometric redshift (photo-z) catalog from the Dark Energy Survey. The luminosity distance is provided by the LIGO/Virgo gravitational wave sky map. Since this GW event has the second-smallest localization volume after GW170817, GW190814 is likely to provide the best constraint on cosmology from a single standard siren without identifying an electromagnetic counterpart. Our analysis uses photo-z probability distribution functions and corrects for photo-z biases. We also reanalyze the binary black hole GW170814 within this updated framework. We explore how our findings impact the H0 constraints from GW170817, the only GW merger associated with a unique host galaxy. From a combination of GW190814, GW170814, and GW170817, our analysis yields ${H}_{0}={72.0}_{-8.2}^{+12}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ (68% highest-density interval, HDI) for a prior in H0 uniform between $[20\mathrm{and}140]\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ . The addition of GW190814 and GW170814 to GW170817 improves the 68% HDI from GW170817 alone by 18%, showing how well-localized mergers without counterparts can provide a significant contribution to standard siren measurements, provided that a complete galaxy catalog is available at the location of the event.
  68. Noll, K., Brown, M., Weaver, H., et al., (including Grundy, W.), 2020, PSJ, 1, 44, Detection of a Satellite of the Trojan Asteroid (3548) EurybatesA Lucy Mission Target
    We describe the discovery of a satellite of the Trojan asteroid (3548) Eurybates in images obtained with the Hubble Space Telescope. The satellite was detected on three separate epochs, two in 2018 September and one in 2020 January. The satellite has a brightness in all three epochs consistent with an effective diameter of d2 = 1.2 0.4 km. The projected separation from Eurybates was s 1700-2300 km and varied in position, consistent with a large range of possible orbits. Eurybates is a target of the Lucy Discovery mission and the early detection of a satellite provides an opportunity for a significant expansion of the scientific return from this encounter.
  69. Pang, X., Li, Y., Tang, S., et al., 2020, ApJL, 900, L4, Different Fates of Young Star Clusters after Gas Expulsion
    We identify structures of the young star cluster NGC 2232 in the solar neighborhood (323.0 pc) and a newly discovered star cluster, LP 2439 (289.1 pc). Member candidates are identified using the Gaia DR2 sky position, parallax, and proper-motion data by an unsupervised machine-learning method, STARGO. Member contamination from the Galactic disk is further removed using the color-magnitude diagram. The four identified groups (NGC 2232, LP 2439, and two filamentary structures) of stars are coeval with an age of 25 Myr and were likely formed in the same giant molecular cloud. We correct the distance asymmetry from the parallax error with a Bayesian method. The 3D morphology shows the two spherical distributions of clusters NGC 2232 and LP 2439. Two filamentary structures are spatially and kinematically connected to NGC 2232. Both NGC 2232 and LP 2439 are expanding. The expansion is more significant in LP 2439, generating a loose spatial distribution with shallow volume number and mass density profiles. The expansion is suggested to be mainly driven by gas expulsion. With 73% of the cluster mass bound, NGC 2232 is currently experiencing a process of revirialization, However, LP 2439, with 52% of the cluster mass unbound, may fully dissolve in the near future. The different survivability traces the different dynamical states of NGC 2232 and LP 2439 prior to the onset of gas expulsion. While NGC 2232 may have been substructured and subvirial, LP 2439 may have either been virial/supervirial or experienced a much faster rate of gas removal.
  70. Guo, H., Burke, C., Liu, X., et al., (including Kuehn, K.), 2020, MNRAS, 496, 3636, Dark Energy Survey identification of a low-mass active galactic nucleus at redshift 0.823 from optical variability
    We report the identification of a low-mass active galactic nucleus (AGN), DES J0218-0430, in a redshift z = 0.823 galaxy in the Dark Energy Survey (DES) Supernova field. We select DES J0218-0430 as an AGN candidate by characterizing its long-term optical variability alone based on DES optical broad-band light curves spanning over 6 yr. An archival optical spectrum from the fourth phase of the Sloan Digital Sky Survey shows both broad Mg II and broad H lines, confirming its nature as a broad-line AGN. Archival XMM-Newton X-ray observations suggest an intrinsic hard X-ray luminosity of $L_{{\rm 2-12\, keV}}\approx 7.6\pm 0.4\times 10^{43}$ erg s-1, which exceeds those of the most X-ray luminous starburst galaxies, in support of an AGN driving the optical variability. Based on the broad H from SDSS spectrum, we estimate a virial black hole (BH) mass of M 106.43-106.72 M (with the error denoting the systematic uncertainty from different calibrations), consistent with the estimation from OzDES, making it the lowest mass AGN with redshift > 0.4 detected in optical. We estimate the host galaxy stellar mass to be M* 1010.5 0.3 M based on modelling the multiwavelength spectral energy distribution. DES J0218-0430 extends the M-M* relation observed in luminous AGNs at z ~ 1 to masses lower than being probed by previous work. Our work demonstrates the feasibility of using optical variability to identify low-mass AGNs at higher redshift in deeper synoptic surveys with direct implications for the upcoming Legacy Survey of Space and Time at Vera C. Rubin Observatory.
  71. Macaulay, E., Bacon, D., Nichol, R., et al., (including Kuehn, K.), 2020, MNRAS, 496, 4051, Weak lensing of Type Ia Supernovae from the Dark Energy Survey
    We consider the effects of weak gravitational lensing on observations of 196 spectroscopically confirmed Type Ia Supernovae (SNe Ia) from years 1 to 3 of the Dark Energy Survey (DES). We simultaneously measure both the angular correlation function and the non-Gaussian skewness caused by weak lensing. This approach has the advantage of being insensitive to the intrinsic dispersion of SNe Ia magnitudes. We model the amplitude of both effects as a function of 8, and find 8 =1.2$^{+0.9}_{-0.8}$. We also apply our method to a subsample of 488 SNe from the Joint Light-curve Analysis (JLA; chosen to match the redshift range we use for this work), and find 8 =0.8$^{+1.1}_{-0.7}$. The comparable uncertainty in 8 between DES-SN and the larger number of SNe from JLA highlights the benefits of homogeneity of the DES-SN sample, and improvements in the calibration and data analysis.
  72. Hartley, W., Chang, C., Samani, S., et al., (including Kuehn, K.), 2020, MNRAS, 496, 4769, The impact of spectroscopic incompleteness in direct calibration of redshift distributions for weak lensing surveys
    Obtaining accurate distributions of galaxy redshifts is a critical aspect of weak lensing cosmology experiments. One of the methods used to estimate and validate redshift distributions is to apply weights to a spectroscopic sample, so that their weighted photometry distribution matches the target sample. In this work, we estimate the selection bias in redshift that is introduced in this procedure. We do so by simulating the process of assembling a spectroscopic sample (including observer-assigned confidence flags) and highlight the impacts of spectroscopic target selection and redshift failures. We use the first year (Y1) weak lensing analysis in Dark Energy Survey (DES) as an example data set but the implications generalize to all similar weak lensing surveys. We find that using colour cuts that are not available to the weak lensing galaxies can introduce biases of up to z ~ 0.04 in the weighted mean redshift of different redshift intervals (z ~ 0.015 in the case most relevant to DES). To assess the impact of incompleteness in spectroscopic samples, we select only objects with high observer-defined confidence flags and compare the weighted mean redshift with the true mean. We find that the mean redshift of the DES Y1 weak lensing sample is typically biased at the z = 0.005-0.05 level after the weighting is applied. The bias we uncover can have either sign, depending on the samples and redshift interval considered. For the highest redshift bin, the bias is larger than the uncertainties in the other DES Y1 redshift calibration methods, justifying the decision of not using this method for the redshift estimations. We discuss several methods to mitigate this bias.
  73. Ragozzine, D., Pincock, S., Porter, S., et al., (including Grundy, W.), 2020, DDA, 52, 203.04, Non-Keplerian Effects in Kuiper Belt Multiples
    As the number of solar system small body multiple systems (including binaries) grows in number and in observational baseline, advanced dynamical modelling will reveal physical, orbital, and spin properties that are currently poorly understood. For example, among Kuiper Belt Objects (KBOs) beyond Neptune, only a few have well determined obliquities, but observations of orbital precession due to non-spherical shapes can identify spin pole directions and obliquities. The ~50 KBO Binaries with known orbital solutions have been heretofore studied assuming Keplerian motion, but evidence suggests that several of these are beginning to show observationally significant non-Keplerian effects. To study these effects, we have developed and validated an n-quadrupole integrator SPINNY (SPIN + N-bodY) which can include all the dominant non-Keplerian effects relevant within observational precision. SPINNY has been combined with advanced Bayesian model fitting for KBO astrometry in a new modeling tool called MultiMoon. We present MultiMoon along with some potential use cases to demonstrate its value. We also present preliminary results on an analysis of the 47171 Lempo (1996 TC36) KBO trinary system.
  74. Walker, C., Hall, J., Allen, L., et al., 2020, BAAS, 52, 0206, Impact of Satellite Constellations on Optical Astronomy and Recommendations Toward Mitigations
    In May 2019 SpaceX launched its first batch of 60 Starlink communication satellites, which surprised astronomers and laypeople with their appearance in the night sky. Astronomers have only now, a little over a year later, accumulated enough observations of constellation satellites like those being launched by SpaceX and OneWeb, and run computer simulations of their likely impact when fully deployed, to thoroughly understand the magnitude and complexity of the problem. This research informed the discussion at the Satellite Constellations 1 (SATCON1) workshop held virtually 29 June to 2 July 2020 and led to recommendations for observatories and constellation operators. The SATCON1 report concludes that the effects on astronomical research and on the human experience of the night sky range from "negligible" to "extreme."
  75. van Belle, G., Collins, M., Guzman, G., et al., (including Mommert, M.), 2020, RNAAS, 4, 148, Improved ASCOM Dome Following
    An improved algorithm for dome following for an altitude-azimuth telescope mount is presented, with a specific implementation in ASCOM.
  76. Brewer, J., Fischer, D., Blackman, R., et al., (including Llama, J.), 2020, AJ, 160, 67, EXPRES. I. HD 3651 as an Ideal RV Benchmark
    The next generation of exoplanet-hunting spectrographs should deliver up to an order of magnitude improvement in radial velocity (RV) precision over the standard 1 ${\rm{m}}\ {{\rm{s}}}^{-1}$ state-of-the-art spectrographs. This advance is critical for enabling the detection of Earth-mass planets around Sun-like stars. New calibration techniques such as laser frequency combs and stabilized etalons ensure that the instrumental stability is well characterized. However, additional sources of error include stellar noise, undetected short-period planets, and telluric contamination. To understand and ultimately mitigate error sources, the contributing terms in the error budget must be isolated to the greatest extent possible. Here, we introduce a new high-cadence RV program, the Extreme Precision Spectrograph (EXPRES) 100 Earths Survey, which aims to identify rocky planets around bright, nearby G and K dwarfs. We also present a benchmark case: the 62 day orbit of a Saturn-mass planet orbiting the chromospherically quiet star, HD 3651. The combination of high eccentricity (0.6) and a moderately long orbital period ensures significant dynamical clearing of any inner planets. Our Keplerian model for this planetary orbit has a residual rms of 58 cm s-1 over a 6 month time baseline. By eliminating significant contributors to the RV error budget, HD 3651 serves as a standard for evaluating the long-term precision of extreme precision RV programs.
  77. de Jaeger, T., Galbany, L., Gonzalez-Gaitan, S., et al., (including Kuehn, K.), 2020, MNRAS, 495, 4860, Studying Type II supernovae as cosmological standard candles using the Dark Energy Survey
    Despite vast improvements in the measurement of the cosmological parameters, the nature of dark energy and an accurate value of the Hubble constant (H0) in the Hubble-Lemaitre law remain unknown. To break the current impasse, it is necessary to develop as many independent techniques as possible, such as the use of Type II supernovae (SNe II). The goal of this paper is to demonstrate the utility of SNe II for deriving accurate extragalactic distances, which will be an asset for the next generation of telescopes where more-distant SNe II will be discovered. More specifically, we present a sample from the Dark Energy Survey Supernova Program (DES-SN) consisting of 15 SNe II with photometric and spectroscopic information spanning a redshift range up to 0.35. Combining our DES SNe with publicly available samples, and using the standard candle method (SCM), we construct the largest available Hubble diagram with SNe II in the Hubble flow (70 SNe II) and find an observed dispersion of 0.27 mag. We demonstrate that adding a colour term to the SN II standardization does not reduce the scatter in the Hubble diagram. Although SNe II are viable as distance indicators, this work points out important issues for improving their utility as independent extragalactic beacons: find new correlations, define a more standard subclass of SNe II, construct new SN II templates, and dedicate more observing time to high-redshift SNe II. Finally, for the first time, we perform simulations to estimate the redshift-dependent distance-modulus bias due to selection effects.
  78. Wiseman, P., Smith, M., Childress, M., et al., (including Kuehn, K.), 2020, MNRAS, 495, 4040, Supernova host galaxies in the dark energy survey: I. Deep coadds, photometry, and stellar masses
    The 5-yr Dark Energy Survey Supernova Programme (DES-SN) is one of the largest and deepest transient surveys to date in terms of volume and number of supernovae. Identifying and characterizing the host galaxies of transients plays a key role in their classification, the study of their formation mechanisms, and the cosmological analyses. To derive accurate host galaxy properties, we create depth-optimized coadds using single-epoch DES-SN images that are selected based on sky and atmospheric conditions. For each of the five DES-SN seasons, a separate coadd is made from the other four seasons such that each SN has a corresponding deep coadd with no contaminating SN emission. The coadds reach limiting magnitudes of order 27 in g band, and have a much smaller magnitude uncertainty than the previous DES-SN host templates, particularly for faint objects. We present the resulting multiband photometry of host galaxies for samples of spectroscopically confirmed type Ia (SNe Ia), core-collapse (CCSNe), and superluminous (SLSNe) as well as rapidly evolving transients (RETs) discovered by DES-SN. We derive host galaxy stellar masses and probabilistically compare stellar-mass distributions to samples from other surveys. We find that the DES spectroscopically confirmed sample of SNe Ia selects preferentially fewer high-mass hosts at high-redshift compared to other surveys, while at low redshift the distributions are consistent. DES CCSNe and SLSNe hosts are similar to other samples, while RET hosts are unlike the hosts of any other transients, although these differences have not been disentangled from selection effects.
  79. Cartwright, R., Beddingfield, C., Nordheim, T., et al., (including Grundy, W.), 2020, ApJL, 898, L22, Evidence for Ammonia-bearing Species on the Uranian Satellite Ariel Supports Recent Geologic Activity
    We investigated whether ammonia-rich constituents are present on the surface of the Uranian moon Ariel by analyzing 32 near-infrared reflectance spectra collected over a wide range of sub-observer longitudes and latitudes. We measured the band areas and depths of a 2.2 m feature in these spectra, which has been attributed to ammonia-bearing species on other icy bodies. Ten spectra display prominent 2.2 m features with band areas and depths >2. We determined the longitudinal distribution of the 2.2 m band, finding no statistically meaningful differences between Ariel's leading and trailing hemispheres, indicating that this band is distributed across Ariel's surface. We compared the band centers and shapes of the five Ariel spectra displaying the strongest 2.2 m bands to laboratory spectra of various ammonia-bearing and ammonium-bearing species, finding that the spectral signatures of the Ariel spectra are best matched by ammonia-hydrates and flash frozen ammonia-water solutions. Our analysis also revealed that four Ariel spectra display 2.24 m bands (>2 band areas and depths), with band centers and shapes that are best matched by ammonia ice. Because ammonia should be efficiently removed over short timescales by ultraviolet photons, cosmic rays, and charged particles trapped in Uranus' magnetosphere, the possible presence of this constituent supports geologic activity in the recent past, such as emplacement of ammonia-rich cryolavas and exposure of ammonia-rich deposits by tectonism, impact events, and mass wasting.
  80. Dimitrova, T., Neugent, K., Levesque, E., et al., (including Massey, P.), 2020, RNAAS, 4, 107, Locating Red Supergiants in the Galaxy IC10
    We use archival near-IR photometry to identify red supergiants (RSGs) in the starburst galaxy IC10. RSGs are the coolest of the evolved massive stars and have K and M spectral types and temperatures below 4100 K. Typically, they can be up to a thousand times the radius of the Sun, and are therefore highly luminous. Using archival 2MASS and UKIRT photometry we transformed J and K colors to effective temperatures and luminosities, which allowed us to identify the RSGs. After applying temperature and luminosity constraints and eliminating foreground stars using Gaia, we arrived at our finalized list of 138 RSGs. Of this list, 26 were confirmed RSGs based on Gaia parallaxes, with the remaining 112 being unconfirmed proposed IC10 RSGs.
  81. Wan, Z., Lewis, G., Li, T., et al., (including Kuehn, K.), 2020, Natur, 583, 768, The tidal remnant of an unusually metal-poor globular cluster
    Globular clusters are some of the oldest bound stellar structures observed in the Universe1. They are ubiquitous in large galaxies and are believed to trace intense star-formation events and the hierarchical build-up of structure2,3. Observations of globular clusters in the Milky Way, and a wide variety of other galaxies, have found evidence for a `metallicity floor', whereby no globular clusters are found with chemical (metal) abundances below approximately 0.3 to 0.4 per cent of that of the Sun4-6. The existence of this metallicity floor may reflect a minimum mass and a maximum redshift for surviving globular clusters to formboth critical components for understanding the build-up of mass in the Universe7. Here we report measurements from the Southern Stellar Streams Spectroscopic Survey of the spatially thin, dynamically cold Phoenix stellar stream in the halo of the Milky Way. The properties of the Phoenix stream are consistent with it being the tidally disrupted remains of a globular cluster. However, its metal abundance ([Fe/H] = -2.7) is substantially below the empirical metallicity floor. The Phoenix stream thus represents the debris of the most metal-poor globular clusters discovered so far, and its progenitor is distinct from the present-day globular cluster population in the local Universe. Its existence implies that globular clusters below the metallicity floor have probably existed, but were destroyed during Galactic evolution.
  82. Margon, B., Massey, P., Neugent, K., et al., 2020, ApJ, 898, 85, A Survey for C II Emission-line Stars in the Large Magellanic Cloud
    We present a narrowband imaging survey of the Large Magellanic Cloud (LMC), designed to isolate the C II 7231, 7236 emission lines in objects as faint as m7400 18. The work is motivated by the recent serendipitous discovery in the LMC of the first confirmed extragalactic [WC11] star, whose spectrum is dominated by C II emission, and the realization that the number of such objects is currently largely unconstrained. The survey, which imaged 50 deg2 using on-band and off-band filters, will significantly increase the total census of these rare stars. In addition, each new LMC [WC] star has a known luminosity, a quantity quite uncertain in the Galactic sample. Multiple known C II emitters were easily recovered, validating the survey design. We find 38 new C II emission candidates; spectroscopy of the complete sample will be needed to ascertain their nature. In a preliminary spectroscopic reconnaissance, we observed three candidates, finding C II emission in each. One is a new [WC11]. Another shows both the narrow C II emission lines characteristic of a [WC11], but also broad emission of C IV, O V, and He II characteristic of a much hotter [WC4] star; we speculate that this is a binary [WC]. The third object shows weak C II emission, but the spectrum is dominated by a dense thicket of strong absorption lines, including numerous O II transitions. We conclude it is likely an unusual hot, hydrogen-poor post-AGB star, possibly in transition from [WC] to white dwarf. Even lacking a complete spectroscopic program, we can infer that late [WC] stars do not dominate the central stars of LMC planetary nebulae, and that the detected C II emitters are largely of an old population.
  83. Plavchan, P., Barclay, T., Gagne, J., et al., (including von Braun, K.), 2020, Natur, 583, E31, Publisher Correction: A planet within the debris disk around the pre-main-sequence star AU Microscopii
    An amendment to this paper has been published and can be accessed via a link at the top of the paper.
  84. Abbott, T., Aguena, M., Alarcon, A., et al., (including Kuehn, K.), 2020, PhRvD, 102, 023509, Dark Energy Survey Year 1 Results: Cosmological constraints from cluster abundances and weak lensing
    We perform a joint analysis of the counts and weak lensing signal of redMaPPer clusters selected from the Dark Energy Survey (DES) Year 1 dataset. Our analysis uses the same shear and source photometric redshifts estimates as were used in the DES combined probes analysis. Our analysis results in surprisingly low values for S8=8(m/0.3 )0.5=0.65 0.04 , driven by a low matter density parameter, m=0.17 9-0.038+0.031, with 8-m posteriors in 2.4 tension with the DES Y1 3x2pt results, and in 5.6 with the Planck CMB analysis. These results include the impact of post-unblinding changes to the analysis, which did not improve the level of consistency with other data sets compared to the results obtained at the unblinding. The fact that multiple cosmological probes (supernovae, baryon acoustic oscillations, cosmic shear, galaxy clustering and CMB anisotropies), and other galaxy cluster analyses all favor significantly higher matter densities suggests the presence of systematic errors in the data or an incomplete modeling of the relevant physics. Cross checks with x-ray and microwave data, as well as independent constraints on the observable-mass relation from Sunyaev-Zeldovich selected clusters, suggest that the discrepancy resides in our modeling of the weak lensing signal rather than the cluster abundance. Repeating our analysis using a higher richness threshold ( 30 ) significantly reduces the tension with other probes, and points to one or more richness-dependent effects not captured by our model.
  85. Hansen, T., Marshall, J., Simon, J., et al., (including Kuehn, K.), 2020, ApJ, 897, 183, Chemical Analysis of the Ultrafaint Dwarf Galaxy Grus II. Signature of High-mass Stellar Nucleosynthesis
    We present a detailed abundance analysis of the three brightest member stars at the top of the giant branch of the ultrafaint dwarf (UFD) galaxy Grus II. All stars exhibit a higher than expected [Mg/Ca] ratio compared to metal-poor stars in other UFD galaxies and in the Milky Way (MW) halo. Nucleosynthesis in high-mass ( $\geqslant $ 20 M) core-collapse supernovae has been shown to create this signature. The abundances of this small sample (three) stars suggests the chemical enrichment of Grus II could have occurred through substantial high-mass stellar evolution, and is consistent with the framework of a top-heavy initial mass function. However, with only three stars it cannot be ruled out that the abundance pattern is the result of a stochastic chemical enrichment at early times in the galaxy. The most metal-rich of the three stars also possesses a small enhancement in rapid neutron-capture (r-process) elements. The abundance pattern of the r-process elements in this star matches the scaled r-process pattern of the solar system and r-process enhanced stars in other dwarf galaxies and in the MW halo, hinting at a common origin for these elements across a range of environments. All current proposed astrophysical sites of r-process element production are associated with high-mass stars, thus the possible top-heavy initial mass function of Grus II would increase the likelihood of any of these events occurring. The time delay between the and r-process element enrichment of the galaxy favors a neutron star merger as the origin of the r-process elements in Grus II. * This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.
  86. Tokovinin, A., Mason, B., Mendez, R., et al., (including Horch, E.), 2020, AJ, 160, 7, Speckle Interferometry at SOAR in 2019
    The results of speckle-interferometric observations at the 4.1 m Southern Astrophysical Research Telescope in 2019 are given, totaling 2555 measurements of 1972 resolved pairs with separations from 15 mas (median 0"21) and magnitude difference up to 6 mag, and non-resolutions of 684 targets. We resolved for the first time 90 new pairs or subsystems in known binaries. This work continues our long-term speckle program. Its main goal is to monitor orbital motion of close binaries, including members of high-order hierarchies and Hipparcos pairs in the solar neighborhood. We give a list of 127 orbits computed using our latest measurements. Their quality varies from excellent (25 orbits of grades 1 and 2) to provisional (47 orbits of grades 4 and 5).
  87. Schaefer, G., Beck, T., Prato, L., et al., 2020, AJ, 160, 35, Orbital Motion, Variability, and Masses in the T Tauri Triple System
    We present results from adaptive optics imaging of the T Tauri triple system obtained at the Keck and Gemini Observatories in 2015-2019. We fit the orbital motion of T Tau Sb relative to Sa and model the astrometric motion of their center of mass relative to T Tau N. Using the distance measured by Gaia, we derived dynamical masses of ${M}_{\mathrm{Sa}}=2.05\pm 0.14$ M and MSb = 0.43 0.06 ${M}_{\odot }$ . The precision in the masses is expected to improve with continued observations that map the motion through a complete orbital period; this is particularly important as the system approaches periastron passage in 2023. Based on published properties and recent evolutionary tracks, we estimate a mass of 2 M for T Tau N, suggesting that T Tau N is similar in mass to T Tau Sa. Narrowband infrared photometry shows that T Tau N remained relatively constant between late 2017 and early 2019 with an average value of K = 5.54 0.07 mag. Using T Tau N to calibrate relative flux measurements since 2015, we found that T Tau Sa varied dramatically between 7.0 and 8.8 mag in the K band over timescales of a few months, while T Tau Sb faded steadily from 8.5 to 11.1 mag in the K band. Over the 27 yr orbital period of the T Tau S binary, both components have shown 3-4 mag of variability in the K band, relative to T Tau N.
  88. Gutierrez, C., Sullivan, M., Martinez, L., et al., (including Kuehn, K.), 2020, MNRAS, 496, 95, DES16C3cje: A low-luminosity, long-lived supernova
    We present DES16C3cje, a low-luminosity, long-lived type II supernova (SN II) at redshift 0.0618, detected by the Dark Energy Survey (DES). DES16C3cje is a unique SN. The spectra are characterized by extremely narrow photospheric lines corresponding to very low expansion velocities of 1500 km s-1, and the light curve shows an initial peak that fades after 50 d before slowly rebrightening over a further 100 d to reach an absolute brightness of Mr -15.5 mag. The decline rate of the late-time light curve is then slower than that expected from the powering by radioactive decay of 56Co, but is comparable to that expected from accretion power. Comparing the bolometric light curve with hydrodynamical models, we find that DES16C3cje can be explained by either (I) a low explosion energy (0.11 foe) and relatively large 56Ni production of 0.075 M from an 15 M red supergiant progenitor typical of other SNe II, or (II) a relatively compact 40 M star, explosion energy of 1 foe, and 0.08 M of 56Ni. Both scenarios require additional energy input to explain the late-time light curve, which is consistent with fallback accretion at a rate of 0.5 10-8 M s-1.
  89. Lidman, C., Tucker, B., Davis, T., et al., (including Kuehn, K.), 2020, MNRAS, 496, 19, OzDES multi-object fibre spectroscopy for the Dark Energy Survey: results and second data release
    We present a description of the Australian Dark Energy Survey (OzDES) and summarize the results from its 6 years of operations. Using the 2dF fibre positioner and AAOmega spectrograph on the 3.9-m Anglo-Australian Telescope, OzDES has monitored 771 active galactic nuclei, classified hundreds of supernovae, and obtained redshifts for thousands of galaxies that hosted a transient within the 10 deep fields of the Dark Energy Survey. We also present the second OzDES data release, containing the redshifts of almost 30 000 sources, some as faint as rAB = 24 mag, and 375 000 individual spectra. These data, in combination with the time-series photometry from the Dark Energy Survey, will be used to measure the expansion history of the Universe out to z 1.2 and the masses of hundreds of black holes out to z 4. OzDES is a template for future surveys that combine simultaneous monitoring of targets with wide-field imaging cameras and wide-field multi-object spectrographs.
  90. Zenteno, A., Hernandez-Lang, D., Klein, M., et al., (including Kuehn, K.), 2020, MNRAS, 495, 705, A joint SZ-X-ray-optical analysis of the dynamical state of 288 massive galaxy clusters
    We use imaging from the first three years of the Dark Energy Survey to characterize the dynamical state of 288 galaxy clusters at 0.1 z 0.9 detected in the South Pole Telescope (SPT) Sunyaev-Zeldovich (SZ) effect survey (SPT-SZ). We examine spatial offsets between the position of the brightest cluster galaxy (BCG) and the centre of the gas distribution as traced by the SPT-SZ centroid and by the X-ray centroid/peak position from Chandra and XMM data. We show that the radial distribution of offsets provides no evidence that SPT SZ-selected cluster samples include a higher fraction of mergers than X-ray-selected cluster samples. We use the offsets to classify the dynamical state of the clusters, selecting the 43 most disturbed clusters, with half of those at z 0.5, a region seldom explored previously. We find that Schechter function fits to the galaxy population in disturbed clusters and relaxed clusters differ at z > 0.55 but not at lower redshifts. Disturbed clusters at z > 0.55 have steeper faint-end slopes and brighter characteristic magnitudes. Within the same redshift range, we find that the BCGs in relaxed clusters tend to be brighter than the BCGs in disturbed samples, while in agreement in the lower redshift bin. Possible explanations includes a higher merger rate, and a more efficient dynamical friction at high redshift. The red-sequence population is less affected by the cluster dynamical state than the general galaxy population.
  91. Pursiainen, M., Gutierrez, C., Wiseman, P., et al., (including Kuehn, K.), 2020, MNRAS, 494, 5576, The mystery of photometric twins DES17X1boj and DES16E2bjy
    We present an analysis of DES17X1boj and DES16E2bjy, two peculiar transients discovered by the Dark Energy Survey (DES). They exhibit nearly identical double-peaked light curves that reach very different maximum luminosities (Mr = -15.4 and -17.9, respectively). The light-curve evolution of these events is highly atypical and has not been reported before. The transients are found in different host environments: DES17X1boj was found near the nucleus of a spiral galaxy, while DES16E2bjy is located in the outskirts of a passive red galaxy. Early photometric data are well fitted with a blackbody and the resulting moderate photospheric expansion velocities (1800 km s-1 for DES17X1boj and 4800 km s-1 for DES16E2bjy) suggest an explosive or eruptive origin. Additionally, a feature identified as high-velocity Ca II absorption ( $v$ 9400 km s-1) in the near-peak spectrum of DES17X1boj may imply that it is a supernova. While similar light-curve evolution suggests a similar physical origin for these two transients, we are not able to identify or characterize the progenitors.
  92. Plavchan, P., Barclay, T., Gagne, J., et al., (including von Braun, K.), 2020, Natur, 582, 497, A planet within the debris disk around the pre-main-sequence star AU Microscopii
    AU Microscopii (AU Mic) is the second closest pre-main-sequence star, at a distance of 9.79 parsecs and with an age of 22 million years1. AU Mic possesses a relatively rare2 and spatially resolved3 edge-on debris disk extending from about 35 to 210 astronomical units from the star4, and with clumps exhibiting non-Keplerian motion5-7. Detection of newly formed planets around such a star is challenged by the presence of spots, plage, flares and other manifestations of magnetic `activity' on the star8,9. Here we report observations of a planet transiting AU Mic. The transiting planet, AU Mic b, has an orbital period of 8.46 days, an orbital distance of 0.07 astronomical units, a radius of 0.4 Jupiter radii, and a mass of less than 0.18 Jupiter masses at 3 confidence. Our observations of a planet co-existing with a debris disk offer the opportunity to test the predictions of current models of planet formation and evolution.
  93. Cowall, D., Skiff, B., Odell, A., 2020, JAVSO, 48, 28, Continued Period Changes in BW Vulpeculae
    BW Vulpeculae (BW Vul) has the largest amplitude of the beta Cephei stars. Over almost 80 years of observations, BW Vul has closely followed a parabolic ephemeris and possibly a light-travel-time effect. This parabola, with excursions on either side, also could be viewed as a sequence of straight lines (constant period) with abrupt period increases. This paradigm predicted a period increase around 2004, which did not occur. A recent observing campaign on this star using the AAVSOnet's Bright Star Monitor telescopes as well as the 0.7-m Lowell Observatory telescope has been undertaken. A period analysis of our data suggests that the period may have paradoxically decreased beginning around 2009. Further observations are necessary to confirm this analysis.
  94. Barrows, R., Comerford, J., Llama, J., et al., (including Prato, L.), 2020, hst, 16362, Redshift Evolution of ULXs
    We propose a project to identify and analyze archival HST imaging of ~200 ultra-luminous X-ray source (ULX) candidates out to intermediate redshifts (z~0.25). ULXs are luminous (LX>10^39 erg/s), off-nuclear X-ray sources in galaxies, and at intermediate redshifts they are expected to contribute significantly to the cosmic X-ray background. They are also unique laboratories for studying the physics of super-Eddington accretion or accretion onto massive stars and stellar remnants. Some ULXs may also represent accretion onto intermediate-mass black holes (IMBHs) that have been deposited into the host galaxy following a merger and may be the seed masses of supermassive black holes. HST is the only observational resource with the imaging resolution and sensitivity to detect intermediate redshift ULX stellar counterparts and to resolve their galactic environments. This project will yield the largest sample of ULXs out to intermediate redshifts studied with HST, and we will use it to conduct four tests designed to elucidate their nature: A) test for likely contaminants (background or foreground sources) based on association with external galaxies; B) test the stellar mass origin or IMBH scenarios by measuring stellar counterpart masses or upper limits; C) test if the ULXs reside in galaxies with enhanced star-formation rates; and D) test if the ULXs reside in locally star-forming environments. The results of these tests will enable, for the first time, a comprehensive view of how ULX properties evolve out to intermediate redshifts. The archival approach of this project will eliminate the burden on HST time while maximizing its contribution to the science of ULXs.
  95. Flagg, L., Shkolnik, E., Weinberger, A., et al., (including Skiff, B.), 2020, ApJ, 896, 153, ACRONYM IV: Three New, Young, Low-mass Spectroscopic Binaries
    As part of our search for new low-mass members of nearby young moving groups (YMGs), we discovered three low-mass, spectroscopic binaries, two of which are not kinematically associated with any known YMG. Using high-resolution optical spectroscopy, we measure the component and systemic radial velocities of the systems, as well as their lithium absorption and H emission, both spectroscopic indicators of youth. One system (2MASS J02543316-5108313, M2.0+M3.0) we confirm as a member of the 40 Myr old Tuc-Hor moving group, but whose binarity was previously undetected. The second young binary (2MASS J08355977-3042306, K5.5+M1.5) is not a kinematic match to any known YMG, but each component exhibits lithium absorption and strong and wide H emission indicative of active accretion, setting an upper age limit of 15 Myr. The third system (2MASS J10260210-4105537, M1.0+M3.0) has been hypothesized in the literature to be a member of the 10 Myr old TW Hya Association, but our measured systemic velocity shows the binary is in fact not part of any known YMG. This last system also has lithium absorption in each component, and has strong and variable H emission, setting an upper age limit of 15 Myr based on the lithium detection.
  96. Pokhrel, R., Gutermuth, R., Betti, S., et al., (including Allen, T.), 2020, ApJ, 896, 60, Star-Gas Surface Density Correlations in 12 Nearby Molecular Clouds. I. Data Collection and Star-sampled Analysis
    We explore the relation between the stellar mass surface density and the mass surface density of molecular hydrogen gas in 12 nearby molecular clouds that are located at <1.5 kpc distance. The sample clouds span an order-of-magnitude range in mass, size, and star formation rates. We use thermal dust emission from Herschel maps to probe the gas surface density and the young stellar objects from the most recent Spitzer Extended Solar Neighborhood Archive catalog to probe the stellar surface density. Using a star-sampled nearest neighbor technique to probe the star-gas surface density correlations at the scale of a few parsecs, we find that the stellar mass surface density varies as a power law of the gas mass surface density, with a power-law index of 2 in all the clouds. The consistent power-law index implies that star formation efficiency is directly correlated with gas column density, and no gas column density threshold for star formation is observed. We compare the observed correlations with the predictions from an analytical model of thermal fragmentation and with the synthetic observations of a recent hydrodynamic simulation of a turbulent star-forming molecular cloud. We find that the observed correlations are consistent for some clouds with the thermal fragmentation model and can be reproduced using the hydrodynamic simulations.
  97. Farkas-Takacs, A., Kiss, C., Vilenius, E., et al., (including Mommert, M.), 2020, A&A, 638, A23, "TNOs are Cool": A survey of the trans-Neptunian region. XV. Physical characteristics of 23 resonant trans-Neptunian and scattered disk objects
    The goal of this work is to determine the physical characteristics of resonant, detached and scattered disk objects in the trans-Neptunian region, observed mainly in the framework of the "TNOs are Cool" Herschel open time key programme. Based on thermal emission measurements with the Herschel/PACS and Spitzer/MIPS instruments, we determine size, albedo, and surface thermal properties for 23 objects using radiometric modeling techniques. This is the first analysis in which the physical properties of objects in the outer resonances are determined for a notable sample. In addition to the results for individual objects, we compared these characteristics with the bulk properties of other populations of the trans-Neptunian region. The newly analyzed objects show a large variety of beaming factors, indicating a diversity of thermal properties, and in general they follow the albedo-color clustering identified earlier for Kuiper belt objects and Centaurs, further strengthening the evidence for a compositional discontinuity in the young Solar System.
  98. Scolnic, D., Smith, M., Massiah, A., et al., (including Kuehn, K.), 2020, ApJL, 896, L13, Supernova Siblings: Assessing the Consistency of Properties of Type Ia Supernovae that Share the Same Parent Galaxies
    While many studies have shown a correlation between properties of the light curves of SNe Ia and properties of their host galaxies, it remains unclear what is driving these correlations. We introduce a new direct method to study these correlations by analyzing "parent" galaxies that host multiple SNe Ia "siblings." Here, we search the Dark Energy Survey SN sample, one of the largest samples of discovered SNe, and find eight galaxies that hosted two likely SNe Ia. Comparing the light-curve properties of these SNe and recovered distances from the light curves, we find no better agreement between properties of SNe in the same galaxy as any random pair of galaxies, with the exception of the SN light-curve stretch. We show at 2.8 significance that at least one-half of the intrinsic scatter of SNe Ia distance modulus residuals is not from common host properties. We also discuss the robustness with which we could make this evaluation with LSST, which will find 100 more pairs of galaxies, and pave a new line of study on the consistency of SNe Ia in the same parent galaxies. Finally, we argue that it is unlikely that some of these SNe are actually single, lensed SN with multiple images.
  99. Ragone-Figueroa, C., Granato, G., Borgani, S., et al., (including West, M.), 2020, MNRAS, 495, 2436, Evolution and role of mergers in the BCG-cluster alignment. A view from cosmological hydrosimulations
    Contradictory results have been reported on the time evolution of the alignment between clusters and their brightest cluster galaxy (BCG). We study this topic by analysing cosmological hydrosimulations of 24 massive clusters with $M_{200}|_{z=0} \gtrsim 10^{15}\, \rm {\, M_{\odot }}$ , plus 5 less massive with $1 \times 10^{14} \lesssim M_{200}|_{z=0} \lesssim 7 \times 10^{14}\, \rm {\, M_{\odot }}$ , which have already proven to produce realistic BCG masses. We compute the BCG alignment with both the distribution of cluster galaxies and the dark matter (DM) halo. At redshift z = 0, the major axes of the simulated BCGs and their host cluster galaxy distributions are aligned on average within 20. The BCG alignment with the DM halo is even tighter. The alignment persists up to z 2 with no evident evolution. This result continues, although with a weaker signal, when considering the projected alignment. The cluster alignment with the surrounding distribution of matter (3R200) is already in place at z 4 with a typical angle of 35, before the BCG-cluster alignment develops. The BCG turns out to be also aligned with the same matter distribution, albeit always to a lesser extent. These results taken together might imply that the BCG-cluster alignment occurs in an outside-in fashion. Depending on their frequency and geometry, mergers can promote, destroy or weaken the alignments. Clusters that do not experience recent major mergers are typically more relaxed and aligned with their BCG. In turn, accretions closer to the cluster elongation axis tend to improve the alignment as opposed to accretions closer to the cluster minor axis.
  100. Devogele, M., MacLennan, E., Gustafsson, A., et al., (including Moskovitz, N., Mommert, M., Skiff, B.), 2020, PSJ, 1, 15, New Evidence for a Physical Link between Asteroids (155140) 2005 UD and (3200) Phaethon
    In 2018, the near-Earth object (155140) 2005 UD (hereafter UD) experienced a close fly by of the Earth. We present results from an observational campaign involving photometric, spectroscopic, and polarimetric observations carried out across a wide range of phase angles (07-88). We also analyze archival NEOWISE observations. We report an absolute magnitude of HV = 17.51 0.02 mag and an albedo of pV = 0.10 0.02. UD has been dynamically linked to Phaethon due their similar orbital configurations. Assuming similar surface properties, we derived new estimates for the diameters of Phaethon and UD of D = 5.4 0.5 km and D = 1.3 0.1 km, respectively. Thermophysical modeling of NEOWISE data suggests a surface thermal inertia of ${\rm{\Gamma }}={300}_{-110}^{+120}$ and regolith grain size in the range of 0.9-10 mm for UD and grain sizes of 3-30 mm for Phaethon. The light curve of UD displays a symmetric shape with a reduced amplitude of Am(0) = 0.29 mag and increasing at a linear rate of 0.017 mag/ between phase angles of 0 and 25. Little variation in light-curve morphology was observed throughout the apparition. Using light-curve inversion techniques, we obtained a sidereal rotation period P = 5.235 0.005 hr. A search for rotational variation in spectroscopic and polarimetric properties yielded negative results within observational uncertainties of 10% m-1 and 16%, respectively. In this work, we present new evidence that Phaethon and UD are similar in composition and surface properties, strengthening the arguments for a genetic relationship between these two objects. * Partially based on data collected with 2 m RCC telescope at Rozhen National Astronomical Observatory.
  101. Mommert, M., Hora, J., Trilling, D., et al., (including Moskovitz, N.), 2020, PSJ, 1, 12, Recurrent Cometary Activity in Near-Earth Object (3552) Don Quixote
    We report on observations of activity in near-Earth object (3552) Don Quixote using the Spitzer Space Telescope and ground-based telescopes around its 2018 perihelion passage. Spitzer observations obtained six months before perihelion show extended emission around the target's nucleus that is most likely caused by molecular band emission from either CO2 or CO, but we find no significant emission from dust. Ground-based optical observations taken close to perihelion reveal for the first time activity in the optical wavelengths, which we attribute to solar light reflected from dust particles. IRAM millimeter radio observations taken around the same time are unable to rule out CO as the driver of the molecular band emission observed with Spitzer. The comparison of the gas activity presented here with observations performed during Don Quixote's previous apparition suggests that activity in Don Quixote is recurrent. We conclude that (3552) Don Quixote is most likely a weakly active comet.
  102. Mommert, M., Trilling, D., Hora, J., et al., (including Moskovitz, N.), 2020, PSJ, 1, 10, Systematic Characterization of and Search for Activity in Potentially Active Asteroids
    We report on our long-term observational campaign to characterize and monitor a select sample of 75 dynamically selected dormant comet candidates and six near-Sun asteroids. Both asteroid subpopulations can be considered likely to display comet-like activity. Dormant comets are currently inactive comet nuclei that can still harbor volatiles in subsurface layers, whereas near-Sun asteroids have extremely low perihelion distances and are thus prone to catastrophic disruption. As a result of our 4 yr long observing campaign, we find only dormant comet 3552 Don Quixote to show activity during our program. We furthermore find that (51 10)% of dynamically selected dormant comet candidates in near-Earth space have comet-like physical properties, as well as (56 16)% of dynamically selected dormant comet candidates in other parts of the solar system. All of our near-Sun asteroid sample targets are of nonprimitive nature, suggesting that primitive near-Sun asteroids are more likely to disrupt than nonprimitives. We furthermore find a significant fraction of our near-Sun asteroid sample to display extremely blue V-I color indices, potentially hinting at physical alterations of surface material close to the Sun.
  103. Smith, M., Sullivan, M., Wiseman, P., et al., (including Kuehn, K.), 2020, MNRAS, 494, 4426, First cosmology results using type Ia supernovae from the Dark Energy Survey: the effect of host galaxy properties on supernova luminosity
    We present improved photometric measurements for the host galaxies of 206 spectroscopically confirmed type Ia supernovae discovered by the Dark Energy Survey Supernova Program (DES-SN) and used in the first DES-SN cosmological analysis. For the DES-SN sample, when considering a 5D (z, x1, c, , ) bias correction, we find evidence of a Hubble residual 'mass step', where SNe Ia in high-mass galaxies (>1010M) are intrinsically more luminous (after correction) than their low-mass counterparts by $\gamma =0.040\pm 0.019$ mag. This value is larger by 0.031 mag than the value found in the first DES-SN cosmological analysis. This difference is due to a combination of updated photometric measurements and improved star formation histories and is not from host-galaxy misidentification. When using a 1D (redshift-only) bias correction the inferred mass step is larger, with $\gamma =0.066\pm 0.020$ mag. The 1D-5D difference for DES-SN is $0.026\pm 0.009$ mag. We show that this difference is due to a strong correlation between host galaxy stellar mass and the x1 component of the 5D distance-bias correction. Including an intrinsic correlation between the observed properties of SNe Ia, stretch and colour, and stellar mass in simulated SN Ia samples, we show that a 5D fit recovers with -9 mmag bias compared to a +2 mmag bias for a 1D fit. This difference can explain part of the discrepancy seen in the data. Improvements in modelling correlations between galaxy properties and SN is necessary to ensure unbiased precision estimates of the dark energy equation of state as we enter the era of LSST.
  104. Muir, J., Bernstein, G., Huterer, D., et al., (including Kuehn, K.), 2020, MNRAS, 494, 4454, Blinding multiprobe cosmological experiments
    The goal of blinding is to hide an experiment's critical results - here the inferred cosmological parameters - until all decisions affecting its analysis have been finalized. This is especially important in the current era of precision cosmology, when the results of any new experiment are closely scrutinized for consistency or tension with previous results. In analyses that combine multiple observational probes, like the combination of galaxy clustering and weak lensing in the Dark Energy Survey (DES), it is challenging to blind the results while retaining the ability to check for (in)consistency between different parts of the data. We propose a simple new blinding transformation, which works by modifying the summary statistics that are input to parameter estimation, such as two-point correlation functions. The transformation shifts the measured statistics to new values that are consistent with (blindly) shifted cosmological parameters while preserving internal (in)consistency. We apply the blinding transformation to simulated data for the projected DES Year 3 galaxy clustering and weak lensing analysis, demonstrating that practical blinding is achieved without significant perturbation of internal-consistency checks, as measured here by degradation of the 2 between the data and best-fitting model. Our blinding method's performance is expected to improve as experiments evolve to higher precision and accuracy.
  105. Lemon, C., Auger, M., McMahon, R., et al., (including Kuehn, K.), 2020, MNRAS, 494, 3491, The STRong lensing Insights into the Dark Energy Survey (STRIDES) 2017/2018 follow-up campaign: discovery of 10 lensed quasars and 10 quasar pairs
    We report the results of the STRong lensing Insights into the Dark Energy Survey (STRIDES) follow-up campaign of the late 2017/early 2018 season. We obtained spectra of 65 lensed quasar candidates with ESO Faint Object Spectrograph and Camera 2 on the NTT and Echellette Spectrograph and Imager on Keck, confirming 10 new lensed quasars and 10 quasar pairs. Eight lensed quasars are doubly imaged with source redshifts between 0.99 and 2.90, one is triply imaged (DESJ0345-2545, z = 1.68), and one is quadruply imaged (quad: DESJ0053-2012, z = 3.8). Singular isothermal ellipsoid models for the doubles, based on high-resolution imaging from SAMI on Southern Astrophysical Research Telescope or Near InfraRed Camera 2 on Keck, give total magnifications between 3.2 and 5.6, and Einstein radii between 0.49 and 1.97 arcsec. After spectroscopic follow-up, we extract multi-epoch grizY photometry of confirmed lensed quasars and contaminant quasar + star pairs from DES data using parametric multiband modelling, and compare variability in each system's components. By measuring the reduced 2 associated with fitting all epochs to the same magnitude, we find a simple cut on the less variable component that retains all confirmed lensed quasars, while removing 94 per cent of contaminant systems. Based on our spectroscopic follow-up, this variability information improves selection of lensed quasars and quasar pairs from 34-45 per cent to 51-70 per cent, with most remaining contaminants being star-forming galaxies. Using mock lensed quasar light curves we demonstrate that selection based only on variability will over-represent the quad fraction by 10 per cent over a complete DES magnitude-limited sample, explained by the magnification bias and hence lower luminosity/more variable sources in quads.
  106. Massey, P., Hillier, D., Morrell, N., et al., 2020, hst, 16299, The Nature of a Newly Discovered Wolf-Rayet Binary: Archetype of Stripping?
    Understanding massive star evolution is important for a variety of astrophysical processes, from the formation of the elements to the generation of gravitational waves as their remnants merge. Wolf-Rayet stars are evolved stars, where the hydrogen has been removed from a massive OB star, and its nuclear burning products revealed at the surface. This stripping can occur either by stellar winds or by interactions in close binaries. Although we expect the latter to be an important mechanism, there are few examples where one can argue which mechanism has been responsible, as even a single WR star may have formed through binary interaction, but merged with its companion. Given the large number of massive stars in binaries, we expect stripped remnants to be common. Binary models suggest these should look like WR stars, but they are curiously absent where we most expect to find them. However, the recent discovery of a WR binary in the LMC matches many of the properties expected for a stripped binary WR. We have obtained extensive ground-based photometry and spectroscopy of this object, and have carried the analysis as far as it is possible. The WR component is of WN4-type, but with intrinsic hydrogen and helium absorption lines. The companion is an "impossible" star, with a sub-solar mass and radius but a very high temperature. We suggest that this is the result of an Algol-like system, with both components having been donors and recipients at some point. This could be the archetype of binary-produced WRs, but we need UV spectra to determine CNO abundances, stellar wind properties, and better estimates of the bolometric luminosity. HST is the only way to achieve this.
  107. Smith, I., Hayne, P., Byrne, S., et al., (including Hanley, J.), 2020, P&SS, 184, 104841, The Holy Grail: A road map for unlocking the climate record stored within Mars' polar layered deposits
    In its polar layered deposits (PLD), Mars possesses a record of its recent climate, analogous to terrestrial ice sheets containing climate records on Earth. Each PLD is greater than 2 km thick and contains thousands of layers, each containing information on the climatic and atmospheric state during its deposition, creating a climate archive. With detailed measurements of layer composition, it may be possible to extract age, accumulation rates, atmospheric conditions, and surface activity at the time of deposition, among other important parameters; gaining the information would allow us to "read" the climate record. Because Mars has fewer complicating factors than Earth (e.g. oceans, biology, and human-modified climate), the planet offers a unique opportunity to study the history of a terrestrial planet's climate, which in turn can teach us about our own planet and the thousands of terrestrial exoplanets waiting to be discovered.

    During a two-part workshop, the Keck Institute for Space Studies (KISS) hosted 38 Mars scientists and engineers who focused on determining the measurements needed to extract the climate record contained in the PLD. The group converged on four fundamental questions that must be answered with the goal of interpreting the climate record and finding its history based on the climate drivers.

    The group then proposed numerous measurements in order to answer these questions and detailed a sequence of missions and architecture to complete the measurements. In all, several missions are required, including an orbiter that can characterize the present climate and volatile reservoirs; a static reconnaissance lander capable of characterizing near surface atmospheric processes, annual accumulation, surface properties, and layer formation mechanism in the upper 50 cm of the PLD; a network of SmallSat landers focused on meteorology for ground truth of the low-altitude orbiter data; and finally, a second landed platform to access ~500 m of layers to measure layer variability through time. This mission architecture, with two landers, would meet the science goals and is designed to save costs compared to a single very capable landed mission. The rationale for this plan is presented below.

    In this paper we discuss numerous aspects, including our motivation, background of polar science, the climate science that drives polar layer formation, modeling of the atmosphere and climate to create hypotheses for what the layers mean, and terrestrial analogs to climatological studies. Finally, we present a list of measurements and missions required to answer the four major questions and read the climate record.

  108. Petersburg, R., Ong, J., Zhao, L., et al., (including Sawyer, D.), 2020, AJ, 159, 187, An Extreme-precision Radial-velocity Pipeline: First Radial Velocities from EXPRES
    The EXtreme-PREcision Spectrograph (EXPRES) is an environmentally stabilized, fiber-fed, R = 137,500, optical spectrograph. It was recently commissioned at the 4.3 m Lowell Discovery Telescope near Flagstaff, Arizona. The spectrograph was designed with a target radial-velocity (RV) precision of 30 cm s-1. In addition to instrumental innovations, the EXPRES pipeline, presented here, is the first on-sky, optical, fiber-fed spectrograph to employ many novel techniques -- including an "extended flat" fiber used for wavelength-dependent quantum efficiency characterization of the CCD, a flat-relative optimal extraction algorithm, chromatic barycentric corrections, chromatic calibration offsets, and an ultra-precise laser frequency comb for wavelength calibration. We describe the reduction, calibration, and RV analysis pipeline used for EXPRES and present an example of our current sub-meter-per-second RV measurement precision, which reaches a formal, single-measurement error of 0.3 m s-1 for an observation with a per-pixel signal-to-noise ratio of 250. These velocities yield an orbital solution on the known exoplanet host 51 Peg that matches literature values with a residual rms of 0.895 m s-1.
  109. Horch, E., van Belle, G., Davidson, J., et al., (including Clark, C.), 2020, AJ, 159, 233, Observations of Binary Stars with the Differential Speckle Survey Instrument. IX. Observations of Known and Suspected Binaries, and a Partial Survey of Be Stars
    We report 370 measures of 170 components of binary and multiple-star systems, obtained from speckle imaging observations made with the Differential Speckle Survey Instrument at Lowell Observatory's Discovery Channel Telescope in 2015 through 2017. Of the systems studied, 147 are binary stars, 10 are seen as triple systems, and 1 quadruple system is measured. Seventy-six high-quality nondetections and 15 newly resolved components are presented in our observations. The uncertainty in relative astrometry appears to be similar to our previous work at Lowell, namely, linear measurement uncertainties of approximately 2 mas, and the relative photometry appears to be uncertain at the 0.1-0.15 mag level. Using these measures and those in the literature, we calculate six new visual orbits, including one for the Be star 66 Oph and two combined spectroscopic-visual orbits. The latter two orbits, which are for HD 22451 (YSC 127) and HD 185501 (YSC 135), yield individual masses of the components at the level of 2% or better, and independent distance measures that in one case agrees with the value found in the Gaia DR2 and in the other disagrees at the 2 level. We find that HD 22451 consists of an F6V+F7V pair with orbital period of 2401.1 3.2 days and masses of 1.342 0.029 and $1.236\pm 0.026\,{M}_{\odot } . For HD 185501, both stars are G5 dwarfs that orbit one another with a period of 433.94 0.15 days, and the masses are 0.898 0.012 and $0.876\pm 0.012\,{M}_{\odot } . We discuss the details of both the new discoveries and the orbit objects.
  110. Blackman, R., Fischer, D., Jurgenson, C., et al., (including Sawyer, D., Llama, J.), 2020, AJ, 159, 238, Performance Verification of the EXtreme PREcision Spectrograph
    The EXtreme PREcision Spectrograph (EXPRES) is a new Doppler spectrograph designed to reach a radial-velocity measurement precision sufficient to detect Earth-like exoplanets orbiting nearby, bright stars. We report on extensive laboratory testing and on-sky observations to quantitatively assess the instrumental radial-velocity measurement precision of EXPRES, with a focused discussion of individual terms in the instrument error budget. We find that EXPRES can reach a single-measurement instrument calibration precision better than 10 cm s-1, not including photon noise from stellar observations. We also report on the performance of the various environmental, mechanical, and optical subsystems of EXPRES, assessing any contributions to radial-velocity error. For atmospheric and telescope related effects, this includes the fast tip-tilt guiding system, atmospheric dispersion compensation, and the chromatic exposure meter. For instrument calibration, this includes the laser fRequency comb (LFC), flat-field light source, CCD detector, and effects in the optical fibers. Modal noise is mitigated to a negligible level via a chaotic fiber agitator, which is especially important for wavelength calibration with the LFC. Regarding detector effects, we empirically assess the impact on the radial-velocity precision due to pixel-position nonuniformities and charge transfer inefficiency (CTI). EXPRES has begun its science survey to discover exoplanets orbiting G-dwarf and K-dwarf stars, in addition to transit spectroscopy and measurements of the Rossiter-McLaughlin effect.
  111. Burke, C., Baldassare, V., Liu, X., et al., (including Kuehn, K.), 2020, ApJL, 894, L5, The Curious Case of PHL 293B: A Long-lived Transient in a Metal-poor Blue Compact Dwarf Galaxy
    We report on small-amplitude optical variability and recent dissipation of the unusually persistent broad emission lines in the blue compact dwarf galaxy PHL 293B. The galaxy's unusual spectral features (P Cygni-like profiles with 800 km s-1 blueshifted absorption lines) have resulted in conflicting interpretations of the nature of this source in the literature. However, analysis of new Gemini spectroscopy reveals the broad emission has begun to fade after being persistent for over a decade prior. Precise difference imaging light curves constructed with the Sloan Digital Sky Survey and the Dark Energy Survey reveal small-amplitude optical variability of 0.1 mag in the g band offset by 100 21 pc from the brightest pixel of the host. The light curve is well-described by an active galactic nuclei (AGN)-like damped random walk process. However, we conclude that the origin of the optical variability and spectral features of PHL 293B is due to a long-lived stellar transient, likely a Type IIn supernova or nonterminal outburst, mimicking long-term AGN-like variability. This work highlights the challenges of discriminating between scenarios in such extreme environments, relevant to searches for AGNs in dwarf galaxies. This is the second long-lived transient discovered in a blue compact dwarf, after SDSS1133. Our result implies such long-lived stellar transients may be more common in metal-deficient galaxies. Systematic searches for low-level variability in dwarf galaxies will be possible with the upcoming Legacy Survey of Space and Time at the Vera C. Rubin Observatory.
  112. van Belle, G., Schaefer, G., von Braun, K., et al., (including Hartman, Z.), 2020, PASP, 132, 054201, HST/FGS Trigonometric Parallaxes of M-dwarf Eclipsing Binaries
    Hubble Space Telescope (HST) Fine Guidance Sensor (FGS) trigonometric parallax observations were obtained to directly determine distances to five nearby M-dwarf/M-dwarf eclipsing binary systems. These systems are intrinsically interesting as benchmark systems for establishing basic physical parameters for low-mass stars, such as luminosity L, and radius R. HST/FGS distances are also one of the few direct checks on Gaia trigonometric parallaxes, given the comparable sensitivity in both magnitude limit and determination of parallactic angles. A spectral energy distribution (SED) fit of each system's blended flux output was carried out, allowing for estimation of the bolometric flux from the primary and secondary components of each system. From the stellar M, L, and R values, the low-mass star relationships between L and M, and R and M, are compared against idealized expectations for such stars. An examination on the inclusion of these close M-dwarf/M-dwarf pairs in higher-order common proper motion (CPM) pairs is analyzed; each of the 5 systems has indications of being part of a CPM system. Unexpected distances on interesting objects found within the grid of parallactic reference stars are also presented, including a nearby M dwarf and a white dwarf.
  113. Drlica-Wagner, A., Bechtol, K., Mau, S., et al., (including Kuehn, K.), 2020, ApJ, 893, 47, Milky Way Satellite Census. I. The Observational Selection Function for Milky Way Satellites in DES Y3 and Pan-STARRS DR1
    We report the results of a systematic search for ultra-faint Milky Way satellite galaxies using data from the Dark Energy Survey (DES) and Pan-STARRS1 (PS1). Together, DES and PS1 provide multi-band photometry in optical/near-infrared wavelengths over 80% of the sky. Our search for satellite galaxies targets 25,000 deg2 of the high-Galactic-latitude sky reaching a 10 point-source depth of 22.5 mag in the g and r bands. While satellite galaxy searches have been performed independently on DES and PS1 before, this is the first time that a self-consistent search is performed across both data sets. We do not detect any new high-significance satellite galaxy candidates, recovering the majority of satellites previously detected in surveys of comparable depth. We characterize the sensitivity of our search using a large set of simulated satellites injected into the survey data. We use these simulations to derive both analytic and machine-learning models that accurately predict the detectability of Milky Way satellites as a function of their distance, size, luminosity, and location on the sky. To demonstrate the utility of this observational selection function, we calculate the luminosity function of Milky Way satellite galaxies, assuming that the known population of satellite galaxies is representative of the underlying distribution. We provide access to our observational selection function to facilitate comparisons with cosmological models of galaxy formation and evolution.
  114. Nadler, E., Wechsler, R., Bechtol, K., et al., (including Kuehn, K.), 2020, ApJ, 893, 48, Milky Way Satellite Census. II. Galaxy-Halo Connection Constraints Including the Impact of the Large Magellanic Cloud
    The population of Milky Way (MW) satellites contains the faintest known galaxies and thus provides essential insight into galaxy formation and dark matter microphysics. Here we combine a model of the galaxy-halo connection with newly derived observational selection functions based on searches for satellites in photometric surveys over nearly the entire high Galactic latitude sky. In particular, we use cosmological zoom-in simulations of MW-like halos that include realistic Large Magellanic Cloud (LMC) analogs to fit the position-dependent MW satellite luminosity function. We report decisive evidence for the statistical impact of the LMC on the MW satellite population due to an estimated 6 2 observed LMC-associated satellites, consistent with the number of LMC satellites inferred from Gaia proper-motion measurements, confirming the predictions of cold dark matter models for the existence of satellites within satellite halos. Moreover, we infer that the LMC fell into the MW within the last 2 Gyr at high confidence. Based on our detailed full-sky modeling, we find that the faintest observed satellites inhabit halos with peak virial masses below $3.2\times {10}^{8}\ {M}_{\odot }$ at 95% confidence, and we place the first robust constraints on the fraction of halos that host galaxies in this regime. We predict that the faintest detectable satellites occupy halos with peak virial masses above ${10}^{6}\ {M}_{\odot }$ , highlighting the potential for powerful galaxy formation and dark matter constraints from future dwarf galaxy searches.
  115. Nesvorny, D., Vokrouhlicky, D., Bottke, W., et al., (including Grundy, W.), 2020, ApJL, 893, L16, Very Slow Rotators from Tidally Synchronized Binaries
    A recent examination of K2 lightcurves indicates that 15% of Jupiter Trojans have very slow rotation (spin periods Ps > 100 hr). Here we consider the possibility that these bodies formed as equal-size binaries in the massive outer disk at 20-30 au. Prior to their implantation as Jupiter Trojans, tight binaries tidally evolved toward a synchronous state with Ps Pb, where Pb is the binary orbit period. They may have been subsequently dissociated by impacts and planetary encounters with at least one binary component retaining its slow rotation. Surviving binaries on Trojan orbits would continue to evolve by tides and spin-changing impacts over 4.5 Gyr. To explain the observed fraction of slow rotators, we find that at least 15%-20% of outer disk bodies with diameters 15 < D < 50 km would have to form as equal-size binaries with 12 ab/R 30, where ab is the binary semimajor axis and R = D/2. The mechanism proposed here could also explain very slow rotators found in other small-body populations.
  116. Coffaro, M., Stelzer, B., Orlando, S., et al., (including Hall, J.), 2020, A&A, 636, A49, An X-ray activity cycle on the young solar-like star Eridani
    Chromospheric Ca II activity cycles are frequently found in late-type stars, but no systematic programs have been created to search for their coronal X-ray counterparts. The typical time scale of Ca II activity cycles ranges from years to decades. Therefore, long-lasting missions are needed to detect the coronal counterparts. The XMM-Newton satellite has so far detected X-ray cycles in five stars. A particularly intriguing question is at what age (and at what activity level) X-ray cycles set in. To this end, in 2015 we started the X-ray monitoring of the young solar-like star Eridani, previously observed on two occasions: in 2003 and in early 2015, both by XMM-Newton. With an age of 440 Myr, it is one of the youngest solar-like stars with a known chromospheric Ca II cycle. We collected the most recent Mount Wilson S-index data available for Eridani, starting from 2002, including previously unpublished data. We found that the Ca II cycle lasts 2.92 0.02 yr, in agreement with past results. From the long-term XMM-Newton lightcurve, we find clear and systematic X-ray variability of our target, consistent with the chromospheric Ca II cycle. The average X-ray luminosity is 2 1028erg s-1, with an amplitude that is only a factor of 2 throughout the cycle. We apply a new method to describe the evolution of the coronal emission measure distribution of Eridani in terms of solar magnetic structures: active regions, cores of active regions, and flares covering the stellar surface at varying filling fractions. Combinations of these three types of magnetic structures can only describe the observed X-ray emission measure of Eridani if the solar flare emission measure distribution is restricted to events in the decay phase. The interpretation is that flares in the corona of Eridani last longer than their solar counterparts. We ascribe this to the lower metallicity of Eridani. Our analysis also revealed that the X-ray cycle of Eridani is strongly dominated by cores of active regions. The coverage fraction of cores throughout the cycle changes by the same factor as the X-ray luminosity. The maxima of the cycle are characterized by a high percentage of covering fraction of the flares, consistent with the fact that flaring events are seen in the corresponding short-term X-ray lightcurves predominately at the cycle maxima. The high X-ray emission throughout the cycle of Eridani is thus explained by the high percentage of magnetic structures on its surface.
  117. Buie, M., Porter, S., Tamblyn, P., et al., (including Wasserman, L., Bosh, A., Levine, S.), 2020, AJ, 159, 130, Size and Shape Constraints of (486958) Arrokoth from Stellar Occultations
    We present the results from four stellar occultations by (486958) Arrokoth, the flyby target of the New Horizons extended mission. Three of the four efforts led to positive detections of the body, and all constrained the presence of rings and other debris, finding none. Twenty-five mobile stations were deployed for 2017 June 3 and augmented by fixed telescopes. There were no positive detections from this effort. The event on 2017 July 10 was observed by the Stratospheric Observatory for Infrared Astronomy with one very short chord. Twenty-four deployed stations on 2017 July 17 resulted in five chords that clearly showed a complicated shape consistent with a contact binary with rough dimensions of 20 by 30 km for the overall outline. A visible albedo of 10% was derived from these data. Twenty-two systems were deployed for the fourth event on 2018 August 4 and resulted in two chords. The combination of the occultation data and the flyby results provides a significant refinement of the rotation period, now estimated to be 15.9380 0.0005 hr. The occultation data also provided high-precision astrometric constraints on the position of the object that were crucial for supporting the navigation for the New Horizons flyby. This work demonstrates an effective method for obtaining detailed size and shape information and probing for rings and dust on distant Kuiper Belt objects as well as being an important source of positional data that can aid in spacecraft navigation that is particularly useful for small and distant bodies.
  118. Mommert, M., 2020, AJ, 159, 178, Cloud Identification from All-sky Camera Data with Machine Learning
    Most ground-based observatories are equipped with wide-angle all-sky cameras to monitor the night sky conditions. Such camera systems can be used to provide an early warning of incoming clouds that can pose a danger to the telescope equipment through precipitation, as well as for sky quality monitoring. We investigate the use of different machine-learning approaches for automating the identification of mostly opaque clouds in all-sky camera data as a cloud warning system. In a deep-learning approach, we train a residual neural network (ResNet) on pre-labeled camera images. Our second approach extracts relevant and localized image features from camera images and uses these data to train a gradient-boosted tree-based model (lightGBM). We train both model approaches on a set of roughly 2000 images taken by the all-sky camera located at Lowell Observatory's Discovery Channel Telescope, in which the presence of clouds has been labeled manually. The ResNet approach reaches an accuracy of 85% in detecting clouds in a given region of an image, but requires a significant amount of computing resources. Our lightGBM approach achieves an accuracy of 95% with a training sample of 1000 images and rather modest computing resources. Based on different performance metrics, we recommend the latter feature-based approach for automated cloud detection. Code that was built for this work is available online.
  119. Marsset, M., DeMeo, F., Binzel, R., et al., (including Burt, B., Moskovitz, N.), 2020, ApJS, 247, 73, Twenty Years of SpeX: Accuracy Limits of Spectral Slope Measurements in Asteroid Spectroscopy
    We examined two decades of SpeX/NASA Infrared Telescope Facility observations from the Small Main-Belt Asteroid Spectroscopic Survey (SMASS) and the MIT-Hawaii Near-Earth Object Spectroscopic Survey (MITHNEOS) to investigate uncertainties and systematic errors in reflectance spectral slope measurements of asteroids. From 628 spectra of 11 solar analogs used for calibration of the asteroid spectra, we derived an uncertainty of on slope measurements over 0.8-2.4 m. Air mass contributes to -0.92% m-1 per 0.1 unit air mass difference between the asteroid and the solar analog and therefore for an overall 2.8% m-1 slope variability in SMASS and MITHNEOS designed to operate within 1.0-1.3 air mass. No additional observing conditions (including the parallactic angle, seeing, and humidity) were found to contribute systematically to slope change. We discuss implications for asteroid taxonomic classification works. Uncertainties provided in this study should be accounted for in future compositional investigation of small bodies to distinguish intrinsic heterogeneities from possible instrumental effects.
  120. Benson, C., Scheeres, D., Moskovitz, N., 2020, Icar, 340, 113518, Spin state evolution of asteroid (367943) Duende during its 2013 earth flyby
    On February 15, 2013 asteroid (367943) Duende, provisionally named 2012 DA14, experienced an extremely close earth encounter, passing within 27,700 km altitude. An observation campaign was made possible by one year's notice of the flyby. This campaign, discussed in detail in the companion paper by Moskovitz et al. (2019), yielded visible-wavelength photometry before and after closest approach. Post-flyby Goldstone Doppler-delay radar data were also obtained. These data indicated a roughly 40 m 20 m object in non-principal axis rotation. Leveraging light curve frequency analysis from the Moskovitz et al. companion paper, dynamical and inertia constraints from the rough radar-derived elongations, and simulated photometry, only two post-flyby states were deemed viable. These were a long axis mode (LAM) with long axis convention periods Pbar = 6.36 h and P = 8.73 h and a short axis mode (SAM) with Pbar = 8.71 h and P = 23.7 h (each with nominal long-intermediate and long-short ellipsoid axis ratios of 1.7:1 and 2.3:1 respectively). The SAM solution was more consistent with the post-flyby photometry and radar data. Nevertheless, there were differences between the amplitude and phase of the post-flyby and best-fit simulated SAM light curves at some epochs. These discrepancies may be due to a non-ellipsoidal shape, non-uniform albedo, and/or incorrect spin state solution (attitude, inertias, tumbling periods, or rotation mode).

    Analysis of the sparse pre-flyby photometry by Moskovitz et al. yielded poor Fourier series solutions for all principal axis states and different peaks in the pre and post-flyby WindowCLEAN power spectra. This suggests the asteroid was tumbling before the encounter and that its spin state changed. Propagating the best-fitting LAM and SAM solutions backwards through the flyby with terrestrial tidal torques resulted in significant dispersion of the rotation states. The pre-flyby SAM states coincided with the notable Moskovitz et al. Fourier solution P1 = 8.37 h and P2 = 24.2 h. Overall, we propose Duende was tumbling before the 2013 flyby and that its spin state may have changed during the flyby. Furthermore, our analysis suggests Duende is currently in SAM with P bar = 8 . 71 h and P = 23.7 h with pole J2000 ecliptic longitude and obliquity of roughly 70 and 95 or 245 and 90 respectively. The spin state characterization approach outlined in this paper could be used for future analyses with inertia, dynamical, and observational constraints.

  121. Moskovitz, N., Benson, C., Scheeres, D., et al., 2020, Icar, 340, 113519, Observational investigation of the 2013 near-Earth encounter by asteroid (367943) Duende
    On 15 February 2013, the asteroid 367943 Duende (2012 DA14) experienced a near-Earth encounter at an altitude of 27,700 km or 4.2 Earth radii. We present here the results of an extensive, multi-observatory campaign designed to probe for spectral and/or rotational changes to Duende due to gravitational interactions with the Earth during the flyby. Our spectral data reveal no changes within systematic uncertainties. Post-flyby lightcurve photometry places strong constraints on the rotation state of Duende, showing that it is in non-principal axis rotation with fundamental periods of P1 = 8.71 0.03 and P2 = 23.7 0.2 h. Multiple lightcurve analysis techniques, coupled with theoretical considerations and delay-Doppler radar imaging, allow us to assign these periods to specific rotational axes of the body. In particular we suggest that Duende is now in a non-principal, short axis mode rotation state with a precessional period equal to P1 and oscillation about the symmetry axis at a rate equal to P2. Temporal and signal-to-noise limitations inherent to the pre-flyby photometric dataset make it difficult to definitively diagnose whether these periods represent a change imparted due to gravitational torques during the flyby. However, based on multiple analysis techniques and a number of plausibility arguments, we suggest that Duende experienced a rotational change during the planetary encounter with an increase in its precessional rotation period. Our preferred interpretation of the available data is that the precession rate increased from 8.4 h prior to the flyby to 8.7 h afterwards. A companion paper by Benson et al. (2019) provides a more detailed dynamical analysis of this event and compares the data to synthetic lightcurves computed from a simple shape model of Duende. The interpretation and results presented in these two works are consistent with one another. The ultimate outcome of this campaign suggests that the analytic tools we employed are sufficient to extract detailed information about solid-body rotation states given data of high enough quality and temporal sampling. As current and future discovery surveys find more near-Earth asteroids, the opportunities to monitor for physical changes during planetary encounters will increase.
  122. Simon, J., Li, T., Erkal, D., et al., (including Kuehn, K.), 2020, ApJ, 892, 137, Birds of a Feather? Magellan/IMACS Spectroscopy of the Ultra-faint Satellites Grus II, Tucana IV, and Tucana V
    We present Magellan/IMACS spectroscopy of three recently discovered ultra-faint Milky Way satellites, Grus II, Tucana IV, and Tucana V. We measure systemic velocities of Vhel = 110.0 0.5 km s-1, Vhel = 15.9-1.7+1.8 km s-1, and Vhel=-36.2-2.2+2.5 km s-1 for the three objects, respectively. Their large relative velocities demonstrate that the satellites are unrelated despite their close physical proximity. We determine a velocity dispersion for Tuc IV of = 4.3-1.0+1.7 km s-1, but we cannot resolve the velocity dispersions of the other two systems. For Gru II, we place an upper limit (90% confidence) on the dispersion of < 1.9 km s-1, and for Tuc V, we do not obtain any useful limits. All three satellites have metallicities below [Fe/H]=-2.1, but none has a detectable metallicity spread. We determine proper motions for each satellite based on Gaia astrometry and compute their orbits around the Milky Way. Gru II is on a tightly bound orbit with a pericenter of 25-7+6 kpc and orbital eccentricity of 0.45-0.05+0.08. Tuc V likely has an apocenter beyond 100 kpc and could be approaching the Milky Way for the first time. The current orbit of Tuc IV is similar to that of Gru II, with a pericenter of 25-8+11 kpc and an eccentricity of 0.36-0.06+0.13. However, a backward integration of the position of Tuc IV demonstrates that it collided with the Large Magellanic Cloud at an impact parameter of 4 kpc 120 Myr ago, deflecting its trajectory and possibly altering its internal kinematics. Based on their sizes, masses, and metallicities, we classify Gru II and Tuc IV as likely dwarf galaxies, but the nature of Tuc V remains uncertain.
  123. Chandler, C., Kueny, J., Trujillo, C., et al., 2020, ApJL, 892, L38, Cometary Activity Discovered on a Distant Centaur: A Nonaqueous Sublimation Mechanism
    Centaurs are minor planets thought to have originated in the outer solar system region known as the Kuiper Belt. Active Centaurs enigmatically display comet-like features (e.g., tails, comae) even though they orbit in the gas giant region where it is too cold for water to readily sublimate. Only 18 active Centaurs have been identified since 1927 and, consequently, the underlying activity mechanism(s) have remained largely unknown up to this point. Here we report the discovery of activity emanating from Centaur 2014 OG392, based on archival images we uncovered plus our own new observational evidence acquired with the Dark Energy Camera (Cerro Tololo Inter-American Observatory Blanco 4 m telescope), the Inamori-Magellan Areal Camera & Spectrograph (Las Campanas Observatory 6.5 m Walter Baade Telescope), and the Large Monolithic Imager (Lowell Observatory 4.3 m Discovery Channel Telescope). We detect a coma as far as 400,000 km from 2014 OG392, and our novel analysis of sublimation processes and dynamical lifetime suggest carbon dioxide and/or ammonia are the most likely candidates for causing activity on this and other active Centaurs. We find 2014 OG392 is optically red, but CO2 and NH3 are spectrally neutral in this wavelength regime so the reddening agent is as yet unidentified.
  124. Hartman, Z., Lepine, S., 2020, ApJS, 247, 66, The SUPERWIDE Catalog: A Catalog of 99,203 Wide Binaries Found in Gaia and Supplemented by the SUPERBLINK High Proper Motion Catalog
    We present a catalog of 99,203 wide binary systems, initially identified as common proper motion (CPM) pairs from a subset of 5.2 million stars with proper motions > 40 mas yr-1, selected from Gaia data release 2 (DR2) and the SUPERBLINK high proper motion catalog. CPM pairs are found by searching for pairs of stars with angular separations <1 and proper motion differences < 40 mas yr-1. A Bayesian analysis is then applied in two steps. In a first pass, we use proper motion differences and angular separations to distinguish between real binaries and chance alignments. In a second pass, we use parallax data from Gaia DR2 to refine our Bayesian probability estimates. We present a table of 119,390 pairs which went through the full analysis, 99,203 of which have probabilities >95% of being real wide binaries. Of those 99,203 high-probability pairs, we estimate that only about 364 pairs are most likely to be false positives. In addition, we identify 57,506 pairs that have probabilities greater than 10% from the first pass but have high parallax errors and therefore were not vetted in the second pass. We examine the projected physical separation distribution of our highest probability pairs and note that the distribution is a simple exponential tail and shows no evidence of being bimodal. Among pairs with lower probability, wide binaries are detected at larger separations (>104-105 au), consistent with the very wide population suggested in previous studies; however, our analysis suggests that these do not represent a distinct population, but instead represent either the exponential tail of the "normal" wide binary distribution or are simply chance alignments of unrelated field stars. We examine the Hertzsprung-Russell diagram of this set of high-probability wide binaries and find evidence for 980 overluminous components among 2227 K + K wide binaries; assuming these represent unresolved subsystems, we determine that the higher-order multiplicity fraction for K + K wide systems is at least 39.6%.
  125. Bourrier, V., Wheatley, P., Lecavelier des Etangs, A., et al., (including Llama, J.), 2020, MNRAS, 493, 559, MOVES III. Simultaneous X-ray and ultraviolet observations unveiling the variable environment of the hot Jupiter HD 189733b
    In this third paper of the MOVES (Multiwavelength Observations of an eVaporating Exoplanet and its Star) programme, we combine Hubble Space Telescope far-ultraviolet (FUV) observations with XMM-Newton/Swift X-ray observations to measure the emission of HD 189733 in various FUV lines, and its soft X-ray spectrum. Based on these measurements we characterize the interstellar medium towards HD 189733 and derive semisynthetic XUV spectra of the star, which are used to study the evolution of its high-energy emission at five different epochs. Two flares from HD 189733 are observed, but we propose that the long-term variations in its spectral energy distribution have the most important consequences for the environment of HD 189733b. Reduced coronal and wind activity could favour the formation of a dense population of Si2+ atoms in a bow-shock ahead of the planet, responsible for pre- and in-transit absorption measured in the first two epochs. In-transit absorption signatures are detected in the Lyman line in the second, third, and fifth epochs, which could arise from the extended planetary thermosphere and a tail of stellar wind protons neutralized via charge-exchange with the planetary exosphere. We propose that increases in the X-ray irradiation of the planet, and decreases in its EUV irradiation causing lower photoionization rates of neutral hydrogen, favour the detection of these signatures by sustaining larger densities of H0 atoms in the upper atmosphere and boosting charge-exchanges with the stellar wind. Deeper and broader absorption signatures in the last epoch suggest that the planet entered a different evaporation regime, providing clues as to the link between stellar activity and the structure of the planetary environment.
  126. Schmidt, C., Baumgardner, J., Moore, L., et al., (including Bida, T.), 2020, PSJ, 1, 4, The Rapid Imaging Planetary Spectrograph: Observations of Mercury's Sodium Exosphere in Twilight
    Ground-based observations of Mercury's exosphere are intrinsically difficult due to its proximity to the Sun and must be made in daylight or during brief windows at twilight. While the dimmer twilight background is far preferred, high airmass seeing and haze through Earth's atmosphere, windshake, and guiding all present formidable challenges toward spatially resolving the exosphere's structure. This study explores how such effects can be mitigated using results from a new instrument for high cadence spectroscopy, the Rapid Imaging Planetary Spectrograph. While high cadence observations do not significantly improve upon the resolution floor imposed by atmospheric seeing, the method does mitigate obstacles such as telescope tracking inaccuracy, windshake, and flux calibration. Whereas daytime observing has been the predominant methodology in past exosphere studies, the twilight observations performed here easily resolve distinct brightness enhancements near 50-60 latitude, just equatorward of magnetic cusp regions. The exosphere in these locations is diagnostic of space weather effects such as charged particle precipitation. The structure in the sodium exosphere generally appears both more extended and brighter over the southern cusp, which has a broader open magnetic field line region. However, a northern enhancement during one observation confirms that the exosphere responds dynamically to environmental drivers, presumably changes in the solar wind dynamic pressure and/or interplanetary magnetic field.
  127. Jenniskens, P., Moskovitz, N., Garvie, L., et al., 2020, M&PS, 55, 535, Orbit and origin of the LL7 chondrite Dishchii'bikoh (Arizona)
    The trajectory and orbit of the LL7 ordinary chondrite Dishchii'bikoh are derived from low-light video observations of a fireball first detected at 10:56:26 UTC on June 2, 2016. Results show a relatively steep ~21 inclined orbit and a short 1.13 AU semimajor axis. Following entry in Earth's atmosphere, the meteor luminosity oscillated corresponding to a meteoroid spin rate of 2.28 0.02 rotations per second. A large fragment broke off at 44 km altitude. Further down, mass was lost to dust during flares at altitudes of 34, 29, and 25 km. Surviving meteorites were detected by Doppler weather radar and several small 0.9-29 g meteorites were recovered under the radar reflection footprint. Based on cosmogenic radionuclides and ground-based radiometric observations, the Dishchii'bikoh meteoroid was 80 20 cm in diameter assuming the density was 3.5 g/cm3. The meteoroid's collisional history confirms that the unusual petrologic class of LL7 does not require a different parent body than three previously observed LL chondrite falls. Dishchii'bikoh was ejected 11 Ma ago from parent body material that has a 4471 6 Ma U-Pb age, the same as that of Chelyabinsk (4452 21 Ma). The distribution of the four known pre-impact LL chondrite orbits is best matched by dynamical modeling if the source of LL chondrites is in the inner asteroid belt in a low inclined orbit, with the highly inclined Dishchii'bikoh being the result of interactions with Earth before impacting.
  128. Hartman, Z., Lepine, S., 2020, CoSka, 50, 446, K dwarf triples and quadruples in the SUPERWIDE catalog of 90,000 nearby wide binaries
    The SUPERWIDE catalog is an all-sky catalog of 90,000 wide binaries with projected orbital separations 100 to 100,000 AU, mostly located within 500 pc of the Sun. These consist of common proper motion (CPM) pairs of high proper motion stars (>40 mas/yr). A Bayesian analysis using positions, proper motions and distances from Gaia Data Release 2 (DR2) shows these pairs to have probabilities >99% of being gravitationally bound systems. Here, we examine K+K wide binaries, which allow for easy identification of unresolved higher-order systems because the K dwarf main sequence is narrow and unresolved subsystems are easily identified as over-luminous. We found 980 systems where at least one of the wide components is over-luminous, which means they are higher-order systems (triples and quadruples). Although metallicity efffects generally complicate the identification of over-luminous stars, we show that this can be easily accounted for in wide binaries, making the identification of unresolved subsystems relatively straightforward. Taking these effects into account, we calculate the higher-order multiplicity fraction to be 39.6%.
  129. Levesque, E., Massey, P., 2020, ApJL, 891, L37, Betelgeuse Just Is Not That Cool: Effective Temperature Alone Cannot Explain the Recent Dimming of Betelgeuse
    We present optical spectrophotometry of the red supergiant (RSG) Betelgeuse from 2020 February 15, during its recent unprecedented dimming episode. By comparing this spectrum to stellar atmosphere models for cool supergiants, as well as spectrophotometry of other Milky Way RSGs, we conclude that Betelgeuse has a current effective temperature of 3600 25 K. While this is slightly cooler than previous measurements taken prior to Betelgeuse's recent lightcurve evolution, this drop in effective temperature is insufficient to explain Betelgeuse's recent optical dimming. We propose that episodic mass loss and an increase in the amount of large-grain circumstellar dust along our sightline to Betelgeuse is the most likely explanation for its recent photometric evolution.
  130. Cartwright, R., Emery, J., Grundy, W., et al., 2020, Icar, 338, 113513, Probing the regoliths of the classical Uranian satellites: Are their surfaces mantled by a layer of tiny H2O ice grains?
    We investigate whether the surfaces of the classical moons of Uranus are compositionally stratified, with a thin veneer of mostly tiny H2O ice grains (2 m diameters) mantling a lower layer composed of larger grains of H2O ice, dark material, and CO2 ice (~10-50 m diameters). Near-infrared observations (~1-2.5 m) have determined that the H2O ice-rich surfaces of these moons are overprinted by concentrated deposits of CO2 ice, found almost exclusively on their trailing hemispheres. However, best fit spectral models of longer wavelength datasets (~3-5 m) indicate that the spectral signature of CO2 ice is largely absent, and instead, the exposed surfaces of these moons are composed primarily of tiny H2O ice grains. To investigate possible compositional layering of these moons, we have collected new data using the Infrared Array Camera (IRAC) onboard the Spitzer Space Telescope (~3-5 m). Spectral modeling of these new data is consistent with prior analyses, suggesting that the exposed surfaces of the Uranian moons are primarily composed of tiny H2O ice grains. Furthermore, analysis of these new data reveal that the trailing hemispheres of these moons are brighter than their leading hemispheres over the 3 to 5 m wavelength range, except for Miranda, which displays no hemispherical asymmetries in its IRAC albedos. Our analyses also reveal that the surface of Ariel displays five distinct, regional-scale albedo zones, possibly consistent with the spatial distribution of CO2 ice on this moon. We discuss possible processes that could be enhancing the observed leading/trailing albedo asymmetries exhibited by these moons, as well as processes that could be driving the apparent compositional stratification of their near surfaces.
  131. Mommert, M., 2020, zndo, Cloud Identification from All-sky Camera Data with Machine Learning, Mommert (2020)
    Code for automatic detection of clouds in allsky camera data as used by astronomical observatories. This code has been built for the publication Cloud Identification from All-sky Camera Data with Machine Learning by Mommert (2020) and has been published by the Astronomical Journal.
  132. Mommert, M., 2020, zndo, Cloud Identification from All-sky Camera Data with Machine Learning, Mommert (2020)
    Code for automatic detection of clouds in allsky camera data as used by astronomical observatories. This code has been built for the publication Cloud Identification from All-sky Camera Data with Machine Learning by Mommert (2020) and has been published by the Astronomical Journal.
  133. Jenniskens, P., Lyytinen, E., Johannink, C., et al., (including Moskovitz, N.), 2020, P&SS, 181, 104829, 2019 outburst of 15-Bootids (IAU#923, FBO) and search strategy to find the potentially hazardous comet
    The CAMS BeNeLux and UAE Astronomical Camera Network meteor shower surveys detected a FWHM = 1.8-h wide outburst of 15-Bootids on April 21/22, 2019. Both networks had clear skies throughout the night, but only between 21h28m and 00h13m UTC were meteors from this shower detected. The measured orbit is that of a Halley-type or Long-Period comet. If the shower is an encounter with the 1-revolution dust trail of a Long-Period comet, then that parent comet is a potential impact hazard. The long duration of the outburst suggests comparatively high ejection speeds from, presumably, a large nucleus. The orbit offers guidance for early comet recovery and a search strategy is described. The orbital elements resemble those of bright comet C/539 W1, which may be the parent comet.
  134. Grundy, W., Bird, M., Britt, D., et al., 2020, Sci, 367, aay3705, Color, composition, and thermal environment of Kuiper Belt object (486958) Arrokoth
    The outer Solar System object (486958) Arrokoth (provisional designation 2014 MU69) has been largely undisturbed since its formation. We studied its surface composition using data collected by the New Horizons spacecraft. Methanol ice is present along with organic material, which may have formed through irradiation of simple molecules. Water ice was not detected. This composition indicates hydrogenation of carbon monoxide-rich ice and/or energetic processing of methane condensed on water ice grains in the cold, outer edge of the early Solar System. There are only small regional variations in color and spectra across the surface, which suggests that Arrokoth formed from a homogeneous or well-mixed reservoir of solids. Microwave thermal emission from the winter night side is consistent with a mean brightness temperature of 29 5 kelvin.
  135. Spencer, J., Stern, S., Moore, J., et al., (including Grundy, W., Wasserman, L.), 2020, Sci, 367, aay3999, The geology and geophysics of Kuiper Belt object (486958) Arrokoth
    The Cold Classical Kuiper Belt, a class of small bodies in undisturbed orbits beyond Neptune, is composed of primitive objects preserving information about Solar System formation. In January 2019, the New Horizons spacecraft flew past one of these objects, the 36-kilometer-long contact binary (486958) Arrokoth (provisional designation 2014 MU69). Images from the flyby show that Arrokoth has no detectable rings, and no satellites (larger than 180 meters in diameter) within a radius of 8000 kilometers. Arrokoth has a lightly cratered, smooth surface with complex geological features, unlike those on previously visited Solar System bodies. The density of impact craters indicates the surface dates from the formation of the Solar System. The two lobes of the contact binary have closely aligned poles and equators, constraining their accretion mechanism.
  136. McKinnon, W., Richardson, D., Marohnic, J., et al., (including Grundy, W.), 2020, Sci, 367, aay6620, The solar nebula origin of (486958) Arrokoth, a primordial contact binary in the Kuiper Belt
    The New Horizons spacecrafts encounter with the cold classical Kuiper Belt object (486958) Arrokoth (provisional designation 2014 MU69) revealed a contact-binary planetesimal. We investigated how Arrokoth formed and found that it is the product of a gentle, low-speed merger in the early Solar System. Its two lenticular lobes suggest low-velocity accumulation of numerous smaller planetesimals within a gravitationally collapsing cloud of solid particles. The geometric alignment of the lobes indicates that they were a co-orbiting binary that experienced angular momentum loss and subsequent merger, possibly because of dynamical friction and collisions within the cloud or later gas drag. Arrokoths contact-binary shape was preserved by the benign dynamical and collisional environment of the cold classical Kuiper Belt and therefore informs the accretion processes that operated in the early Solar System.
  137. Mau, S., Cerny, W., Pace, A., et al., (including Kuehn, K.), 2020, ApJ, 890, 136, Two Ultra-faint Milky Way Stellar Systems Discovered in Early Data from the DECam Local Volume Exploration Survey
    We report the discovery of two ultra-faint stellar systems found in early data from the DECam Local Volume Exploration survey (DELVE). The first system, Centaurus I (DELVE J1238-4054), is identified as a resolved overdensity of old and metal-poor stars with a heliocentric distance of ${\text{}}{D}_{\odot }={116.3}_{-0.6}^{+0.6}\,\mathrm{kpc}$ , a half-light radius of ${r}_{h}={2.3}_{-0.3}^{+0.4}\,\mathrm{arcmin}$ , an age of $\tau \gt 12.85\,\mathrm{Gyr}$ , a metallicity of $Z={0.0002}_{-0.0002}^{+0.0001}$ , and an absolute magnitude of ${M}_{V}=-{5.55}_{-0.11}^{+0.11}\,\mathrm{mag}$ . This characterization is consistent with the population of ultra-faint satellites and confirmation of this system would make Centaurus I one of the brightest recently discovered ultra-faint dwarf galaxies. Centaurus I is detected in Gaia DR2 with a clear and distinct proper motion signal, confirming that it is a real association of stars distinct from the Milky Way foreground; this is further supported by the clustering of blue horizontal branch stars near the centroid of the system. The second system, DELVE 1 (DELVE J1630-0058), is identified as a resolved overdensity of stars with a heliocentric distance of ${\text{}}{D}_{\odot }={19.0}_{-0.6}^{+0.5}\,\mathrm{kpc}$ , a half-light radius of ${r}_{h}={0.97}_{-0.17}^{+0.24}\,\mathrm{arcmin}$ , an age of $\tau ={12.5}_{-0.7}^{+1.0}\,\mathrm{Gyr}$ , a metallicity of $Z={0.0005}_{-0.0001}^{+0.0002}$ , and an absolute magnitude of ${M}_{V}=-{0.2}_{-0.6}^{+0.8}\,\mathrm{mag}$ , consistent with the known population of faint halo star clusters. Given the low number of probable member stars at magnitudes accessible with Gaia DR2, a proper motion signal for DELVE 1 is only marginally detected. We compare the spatial position and proper motion of both Centaurus I and DELVE 1 with simulations of the accreted satellite population of the Large Magellanic Cloud (LMC) and find that neither is likely to be associated with the LMC.
  138. Protopapa, S., Olkin, C., Grundy, W., et al., 2020, AJ, 159, 74, Disk-resolved Photometric Properties of Pluto and the Coloring Materials across its Surface
    A multiwavelength regionally dependent photometric analysis of Pluto's anti-Charon-facing hemisphere using images collected by New Horizons' Multispectral Visible Imaging Camera (MVIC) reveals large variations in the absolute value and spectral slope of the single-scattering albedo. Four regions of interest are analyzed: the dark equatorial belt, Pluto's north pole, nitrogen-rich regions, and the mid-latitude terrains. Regions dominated by volatile ices such as Lowell Regio and Sputnik Planitia present single-scattering albedos of 0.98 at 492 nm, almost neutral across MVIC's visible wavelength range (400-910 nm), indicating limited contributions from tholin materials. Pluto's dark equatorial regions, informally named Cthulhu and Krun Maculae, have single-scattering albedos of 0.16 at 492 nm and are the reddest regions. Applying the Hapke radiative transfer model to combined MVIC and Linear Etalon Imaging Spectral Array (LEISA) spectra (400-2500 nm) of Cthulhu Macula and Lowell Regio successfully reproduces the spectral properties of these two regions of dramatically disparate coloration, composition, and morphology. Since this model uses only a single coloring agent, very similar to the Titan-like tholin of Khare et al., to account for all of Pluto's colors, this result supports the Grundy et al. conclusion that Pluto's coloration is the result of photochemical products mostly produced in the atmosphere. Although cosmic rays and extreme ultraviolet photons reach Pluto's surface where they can drive chemical processing, observations of diverse surface colors do not require different chemical products produced in different environments. We report a correction scaling factor in the LEISA radiometric calibration of 0.74 0.05.
  139. Benson, C., Scheeres, D., Ryan, W., et al., (including Moskovitz, N.), 2020, AcAau, 167, 212, GOES spin state diversity and the implications for GEO debris mitigation
    Many defunct satellites in geosynchronous earth orbit (GEO) spin rapidly or have highly evolving spin states, with some transitioning between uniform and non-principal axis rotation (tumbling). It is hypothesized that the observed evolution of some defunct GEO satellites is caused by the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect and internal energy dissipation. YORP torques are generated by the absorption, reflection, and thermal re-emission of solar radiation and are known to cause secular changes in asteroid spin rates and obliquities. The defunct GOES 8 satellite is particularly notable. This satellite's uniform spin rate rapidly decreased in 2014 and it began tumbling. In this paper, newly analyzed light curve observations of the five nearly identical defunct GOES 8-12 satellites obtained between 2014 and 2018 are presented. The observations show large diversity in evolutionary time histories, with several satellites in consistent slow tumbling, GOES 10 in fast uniform rotation, and GOES 8 transitioning between both. To better understand this diversity, YORP dynamical models are investigated. They reveal that YORP driven spin state evolution is strongly dictated by end of life appendage orientations, which differ among the five satellites. The known end of life configurations are consistent with the observed evolution of GOES 8 and GOES 10. This provides a plausible explanation for the observed spin state diversity. Implications of the observed and simulated evolution for GEO debris mitigation are discussed.
  140. Liang, W., Johnson, J., Hayes, A., et al., (including Grundy, W.), 2020, Icar, 335, 113361, Spectrophotometry from Mars Hand Lens Imager goniometer measurements: Kimberley region, Gale crater
    The light-scattering properties of surface materials on Mars are typically modeled using in situ spectrophotometric imaging sequences taken at multiple times of day to provide sufficient phase coverage. Herein, we report analyses of observations acquired at one time of day but under varying emission angles using the Mars Hand Lens Imager (MAHLI) on the robotic arm of the Mars Science Laboratory (MSL) rover as a goniometer. A multiple-viewpoint data set was acquired on Sol 544 by manipulating the arm to provide MAHLI images from 20 arm positions, all centered at the same location and from a near-constant distance of 1 m from the surface, permitting a phase angle coverage from 8 to 100. From these images, we constructed a digital terrain model of the scene, and used it in combination with atmospheric scattering models to remove the diffuse components of radiance from surface units. Radiative transfer models using Hapke theory were conducted using the direct radiance components from specific rock and soil units. Despite the relatively limited number of observations, our modeled Hapke parameters were well-constrained for terrain types such as soils and certain types of rocks that were common within the scene, but the errors increased for rock types with fewer observations. Results from one-term and two-term Henyey-Greenstein phase functions show the soil units to be more backscattering than rocks, consistent with previous photometric studies of martian landing sites. Overall, we find that the MAHLI goniometer sequences can produce reasonable and consistent photometric results, providing a new and efficient means of acquiring spectrophotometric data by arm cameras on rovers such as MSL.
  141. Beddingfield, C., Beyer, R., Singer, K., et al., (including Grundy, W.), 2020, Icar, 335, 113383, Landslides on Charon
    We investigated five large landslides identified in the Serenity Chasma region of Charon. The identification of these landslides involved a search for these features in images taken by cameras onboard the New Horizons spacecraft. Various landslide properties were analyzed based on their morphologies using a digital terrain model of the region. We found that landslides are confined to the walls of the large normal fault scarps that make up Serenity Chasma. Based on extensive landslide runout lengths (L) relative to their drop heights (H), we classified these features as long-runout landslides. By analyzing their geometries, we estimated the friction coefficients of the landslide material (H/L) to be between 0.15 to 0.31 and the runout efficiencies (L/H) to be between 3.2 and 6.8. We also estimated that the specific energy released during landslide motion ranged from 0.8 to 1.3 kJ kg-1. These amounts of energy were too low to have generated significant melt around landslide particles.
  142. Neugent, K., Massey, P., Georgy, C., et al., (including Mommert, M.), 2020, ApJ, 889, 44, The Luminosity Function of Red Supergiants in M31
    The mass-loss rates of red supergiant stars (RSGs) are poorly constrained by direct measurements, and yet the subsequent evolution of these stars depends critically on how much mass is lost during the RSG phase. In 2012 the Geneva evolutionary group updated their mass-loss prescription for RSGs with the result that a 20 M star now loses 10 times more mass during the RSG phase than in the older models. Thus, higher-mass RSGs evolve back through a second yellow supergiant phase rather than exploding as Type II-P supernovae, in accord with recent observations (the so-called "RSG Problem"). Still, even much larger mass-loss rates during the RSG phase cannot be ruled out by direct measurements of their current dust-production rates, as such mass loss is episodic. Here, we test the models by deriving a luminosity function for RSGs in the nearby spiral galaxy, M31, which is sensitive to the total mass loss during the RSG phase. We carefully separate RSGs from asymptotic giant branch stars in the color-magnitude diagram following the recent method exploited by Yang and collaborators in their Small Magellanic Cloud studies. Comparing our resulting luminosity function with that predicted by the evolutionary models shows that the new prescription for RSG mass loss does an excellent job of matching the observations, and we can readily rule out significantly larger values.
  143. Sokal, K., Johns-Krull, C., Mace, G., et al., (including Nofi, L., Prato, L.), 2020, ApJ, 888, 116, The Mean Magnetic Field Strength of CI Tau
    We present a blind comparison of two methods to measure the mean surface magnetic field strength of the classical T Tauri star CI Tau based on Zeeman broadening of sensitive spectral lines. Our approach takes advantage of the greater Zeeman broadening at near-infrared compared to optical wavelengths. We analyze a high signal-to-noise, high spectral resolution spectrum from 1.5 to 2.5 m observed with IGRINS (Immersion GRating INfrared Spectrometer) on the Discovery Channel Telescope. Both stellar parameterization with MoogStokes (which assumes a uniform magnetic field) and modeling with SYNTHMAG (which includes a distribution of magnetic field strengths) yield consistent measurements for the mean magnetic field strength of CI Tau is B of 2.2 kG. This value is typical compared with measurements for other young T Tauri stars and provides an important contribution to the existing sample given that it is the only known developed planetary system hosted by a young classical T Tauri star. Moreover, we potentially identify an interesting and suggestive trend when plotting the effective temperature and the mean magnetic field strength of T Tauri stars. While a larger sample is needed for confirmation, this trend only appears for a subset of the sample, which may have implications regarding the magnetic field generation.
  144. Koposov, S., Boubert, D., Li, T., et al., (including Kuehn, K.), 2020, MNRAS, 491, 2465, Discovery of a nearby 1700 km s-1 star ejected from the Milky Way by Sgr A*
    We present the serendipitous discovery of the fastest main-sequence hyper-velocity star (HVS) by the Southern Stellar Stream Spectroscopic Survey (S5). The star S5-HVS1 is a 2.35 M A-type star located at a distance of 9 kpc from the Sun and has a heliocentric radial velocity of 1017 2.7 km s^{-1} without any signature of velocity variability. The current 3D velocity of the star in the Galactic frame is 1755 50 km s^{-1}. When integrated backwards in time, the orbit of the star points unambiguously to the Galactic Centre, implying that S5-HVS1 was kicked away from Sgr A* with a velocity of 1800 km s^{-1} and travelled for 4.8 Myr to its current location. This is so far the only HVS confidently associated with the Galactic Centre. S5-HVS1 is also the first hyper-velocity star to provide constraints on the geometry and kinematics of the Galaxy, such as the Solar motion Vy, = 246.1 5.3 km s^{-1} or position R0 = 8.12 0.23 kpc. The ejection trajectory and transit time of S5-HVS1 coincide with the orbital plane and age of the annular disc of young stars at the Galactic Centre, and thus may be linked to its formation. With the S5-HVS1 ejection velocity being almost twice the velocity of other hyper-velocity stars previously associated with the Galactic Centre, we question whether they have been generated by the same mechanism or whether the ejection velocity distribution has been constant over time.
  145. Sickafoose, A., Bosh, A., Emery, J., et al., 2020, MNRAS, 491, 3643, Characterization of material around the centaur (2060) Chiron from a visible and near-infrared stellar occultation in 2011
    The centaur (2060) Chiron exhibits outgassing behaviour and possibly hosts a ring system. On 2011 November 29, Chiron occulted a fairly bright star (R 15 mag) as observed from the 3-m NASA Infrared Telescope Facility (IRTF) on Mauna Kea and the 2-m Faulkes Telescope North (FTN) at Haleakala. Data were taken as visible wavelength images and simultaneous, low-resolution, near-infrared (NIR) spectra. Here, we present a detailed examination of the light-curve features in the optical data and an analysis of the NIR spectra. We place a lower limit on the spherical diameter of Chiron's nucleus of 160.2 1.3 km. Sharp, narrow dips were observed between 280 and 360 km from the centre (depending on event geometry). For a central chord and assumed ring plane, the separated features are 298.5-302 and 308-310.5 km from the nucleus, with normal optical depth 0.5-0.9, and a gap of 9.1 1.3 km. These features are similar in equivalent depth to Chariklo's inner ring. The absence of absorbing/scattering material near the nucleus suggests that these sharp dips are more likely to be planar rings than a shell of material. The region of relatively increased transmission is within the 1:2 spin-orbit resonance, consistent with the proposed clearing pattern for a non-axisymmetric nucleus. Characteristics of possible azimuthally incomplete features are presented, which could be transient, as well as a possible shell from 900-1500 km: future observations are needed for confirmation. There are no significant features in the NIR light curves, nor any correlation between optical features and NIR spectral slope.
  146. Jardine, M., Collier Cameron, A., Donati, J., et al., 2020, MNRAS, 491, 4076, Slingshot prominences: coronal structure, mass-loss, and spin-down
    The structure of a star's coronal magnetic field is a fundamental property that governs the high-energy emission from the hot coronal gas and the loss of mass and angular momentum in the stellar wind. It is, however, extremely difficult to measure. We report a new method to trace this structure in rapidly rotating young convective stars, using the cool gas trapped on coronal field lines as markers. This gas forms 'slingshot prominences' that appear as transient absorption features in H . By using different methods of extrapolating this field from the surface measurements, we determine locations for prominence support and produce synthetic H stacked spectra. The absorption features produced with a potential field extrapolation match well those observed, while the absorption features from a non-potential field do not. In systems where the rotation and magnetic axes are well aligned, up to 50 per cent of the prominence mass may transit the star and so produces a observable feature. This fraction may fall as low as ~2 per cent in very highly inclined systems. Ejected prominences carry away mass and angular momentum at rates that vary by two orders of magnitude, but which may approach those carried by the stellar wind.
  147. Weistrop, D., Nelson, C., Angione, R., et al., 2020, AJ, 159, 17, Physical Properties of the Star-forming Regions in the Interacting Galaxies NGC 3395/NGC 3396
    We report long-slit spectroscopy of the early major merger galaxies NGC 3395/NGC 3396. The spectra are consistent with those for star-forming galaxies, but there is some indication of LINER-like active galactic nucleus activity in the center of NGC 3396. The total star formation rate in the regions observed is 2.83 M yr-1, consistent with estimates for the entire galaxies. The highest abundances are in the centers of the galaxies, with the abundances decreasing with distance. There is a correlation between high abundance and high ionization parameter, both of which can be attributed to the presence of massive stars. Modeling with SB 99 indicates the star-forming regions are younger than 10 Myr. There are 1000-2000 WNL stars in the system, along with several thousand O stars, consistent with the ages of the star-forming regions. The highest electron densities are found in young regions with high star formation rates. The electron temperatures are higher than results for non-interacting galaxies, which is probably due to shock waves produced by the galaxy-galaxy interaction, the outflow of gas from massive stars, and/or collisions between gas clouds in the galaxies. There is star formation in the bridge of material between the galaxies. These regions are among the youngest in the system and have low abundances, suggesting the gas was pulled from the outer parts of the galaxies. X-ray point sources, probably high-mass X-ray binaries, are associated with several star-forming regions.
  148. Rabinowitz, D., Benecchi, S., Grundy, W., et al., (including Thirouin, A.), 2020, AJ, 159, 27, The Complex Rotational Light Curve of (385446) Manwe-Thorondor, a Multicomponent Eclipsing System in the Kuiper Belt
    Kuiper Belt Object (385446) Manwe-Thorondor is a multiobject system with mutual events predicted to occur from 2014 to 2019. To detect the events, we observed the system at 4 epochs (UT 2016 August 25 and 26, 2017 July 22 and 25, 2017 November 9, and 2018 October 6) in g, r, and VR bands using the 4 m SOAR and the 8.1 m Gemini South telescopes at Cerro Pachon, Chile, and Lowell Observatorys 4.3 m Discovery Channel Telescope at Happy Jack, Arizona. These dates overlap the uncertainty range (0.5 day) for four inferior events (Thorondor eclipsing Manwe). We clearly observe variability for the unresolved system with a double-peaked period 11.88190 0.00005 hr and 0.5 mag amplitude together with much longer-term variability. Using a multicomponent model, we simultaneously fit our observations and earlier photometry measured separately for Manwe and Thorondor with the Hubble Space Telescope. Our fit suggests Manwe is bilobed, close to the barbell shape expected for a strengthless body with density 0.8 g cm-3 in hydrostatic equilibrium. For Manwe, we thereby derive maximum width to length ratio 0.30, surface area equivalent to a sphere of diameter 190 km, geometric albedo 0.06, mass 1.4 1018 kg, and spin axis oriented 75 from Earths line of sight. Changes in Thorondors brightness by 0.6 mag with a 300 day period may account for the systems long-term variability. Mutual events with unexpectedly shallow depth and short duration may account for residuals to the fit. The system is complex, providing a challenging puzzle for future modeling efforts.
  149. Lopez-Rodriguez, E., Dowell, C., Jones, T., et al., (including Hamilton, R.), 2020, ApJ, 888, 66, SOFIA/HAWC+ Traces the Magnetic Fields in NGC 1068
    We report the first detection of galactic spiral structure by means of thermal emission from magnetically aligned dust grains. Our 89 m polarimetric imaging of NGC 1068 with the High-resolution Airborne Wideband Camera/Polarimeter (HAWC+) on NASAs Stratospheric Observatory for Infrared Astronomy (SOFIA) also sheds light on magnetic field structure in the vicinity of the galaxy's inner-bar and active galactic nucleus (AGN). We find correlations between the 89 m magnetic field vectors and other tracers of spiral arms, and a symmetric polarization pattern as a function of the azimuthal angle arising from the projection and inclination of the disk field component in the plane of the sky. The observations can be fit with a logarithmic spiral model with pitch angle of {16.9}-2.8+2.7\circ and a disk inclination of 48 2. We infer that the bulk of the interstellar medium from which the polarized dust emission originates is threaded by a magnetic field that closely follows the spiral arms. Inside the central starburst disk (<1.6 kpc), the degree of polarization is found to be lower than for far-infrared sources in the Milky Way, and has minima at the locations of most intense star formation near the outer ends of the inner-bar. Inside the starburst ring, the field direction deviates from the model, becoming more radial along the leading edges of the inner-bar. The polarized flux and dust temperature peak 3-6 NE of the AGN at the location of a bow shock between the AGN outflow and the surrounding interstellar medium, but the AGN itself is weakly polarized (<1%) at both 53 and 89 m.
  150. Ramiaramanantsoa, T., Shkolnik, E., Ardila, D., et al., (including Llama, J.), 2020, AAS, 235, 132.05, M dwarf activity and flaring in the ultraviolet domain with the Star-Planet Activity Research CubeSat (SPARCS)
    With the increasing number of exoplanets discovered in the habitable zones of M dwarfs, the necessity for tighter constraints on the conditions for habitability around cool low-mass stars is rapidly growing. Theoretical studies suggest that the strong and highly variable ultraviolet (UV) radiation of M dwarfs is a key factor influencing the habitability and atmospheric loss of their planets. However, those studies lack sufficient observational constraints. The Star-Planet Activity Research CubeSat (SPARCS) is a NASA-funded mission intended to be inserted into a low-Earth, Sun-synchronous orbit, and will perform photometric monitoring of the chromospheric activity of M stars of various ages, both at far-UV and the near-UV wavelengths. The SPARCS science instrument is composed of a 9-cm Ritchey-Chretien telescope, at the focal plane of which lie two back-illuminated, delta-doped CCDs with high quantum efficiency in UV domain. An active thermal control system will maintain the temperatures of the detectors at -35C to minimize dark-current effects. The detectors' thermal control will be commanded through a dedicated payload processor, which will also perform onboard image processing and trigger changes in detector gain and exposure time upon flare detection. The mission is currently in its development phase, with finalized designs for the telescope, camera, instrument optical bench and thermal system. Besides its science goals, SPARCS will also serve as a technology demonstration by paving the way for the use of high-sensitivity UV-optimized detectors in missions like LUVOIR or HabEx. Acknowledgements: Funding for SPARCS is provided by NASA's Astrophysics Research and Analysis program, NNH16ZDA001N.
  151. Osby, E., Ardila, D., Barman, T., et al., (including Llama, J.), 2020, AAS, 235, 150.08, Photometric Color Correction of the Star Planet Activity Research CubeSat (SPARCS)
    The Star Planet Activity Research CubeSat (SPARCS) will be a 6U CubeSat devoted to photometric monitoring of M dwarfs in the far-ultraviolet (UV) and near-UV (160 and 280 nm respectively), measuring the time-dependent spectral slope, intensity and evolution of M dwarf stellar UV radiation. The delta-doped detectors baselined for SPARCS have demonstrated more than five times the in-band quantum efficiency of the detectors of GALEX. Given that red:UV photon emission from cool, low-mass stars can be ~million:one, UV observation of such stars are susceptible to red light contamination. In addition to the high efficiency delta-doped detectors, SPARCS will include red-rejection filters to help minimize red leak. Even so, careful red-rejection and photometric calibration is needed. As was done for GALEX, white dwarfs are used for photometric calibration in the UV. We find that the use of white dwarfs to calibrate the observations of red stars leads to significant errors in the reported flux, due to the differences in white dwarf and red dwarf spectra. Here we discuss the planned SPARCS calibration model and the color correction, and demonstrate the importance of this correction when recording UV measurements of M stars taken by SPARCS. Funding for SPARCS is provided by NASA's Astrophysics Research and Analysis program, NNH16ZDA001N.
  152. Kuehn, K., S5 Collaboration, 2020, AAS, 235, 156.05, Highlights from the Southern Stellar Stream Spectroscopic Survey
    Stellar streams, produced by the tidal disruption of dwarf galaxies and globular clusters, yield a snapshot of hierarchical structure formation, and are powerful probes of the mass and profile of the Milky Way's dark matter halo, as well as the formation of its stellar halo. Over the last several years, large imaging surveys have increased the number of known stellar streams to over 60. Spectroscopic follow-up observations are crucial, not only for confirming the nature of the streams, but also for determining their full 6D kinematics, metallicities, orbits, progenitors, and formation histories. The Southern Stellar Stream Spectroscopic Survey (S5) began observing the streams recently discovered by the Dark Energy Survey in 2018, and expanded beyond the DES footprint in 2019. S5 employs the large FoV of AAT and high multiplex of 2dF+AAOmega to obtain kinematic measurements along the spatial extent of the tidal streams. We highlight the most important results from our first observational campaigns, including confirmation of at least seven streams using velocities and metallicities of the members stars. We also report on the serendipitous discovery one of the highest velocity stars in the galaxy, S5-HVS1. This star provides the first direct proof of the Hills Mechanism, in which one star in a binary pair is captured by a supermassive black hole (in this case, Sagittarius A*), while its companion is ejected at extremely high speed.
  153. Kuehn, K., Schindler, K., 2020, AAS, 235, 181.01, The Telescopes of Lowell Observatory: the First 125 Years
    From its founding by Percival Lowell 125 years ago, Lowell Observatory has maintained an impressive suite of scientifically productive telescopes. While Lowell's original site (and telescopes) on Mars Hill in Flagstaff, AZ, is now primarily used for public education, outreach, and historical preservation, the Observatory has over its lifetime expanded to multiple additional sites, including Anderson Mesa, which houses 31" and 42" telescopes as well as the Navy Precision Optical Interferometer, and Happy Jack, which hosts the 4.3m Discovery Channel Telescope, one of the newest and most advanced 4m-class telescopes on the planet. We describe the evolution of Lowell Observatory's telescopes and accompanying instrumentation, from its beginnings to the present day, and highlight the most impactful discoveries made by the Observatory's astronomers.
  154. Prato, L., Schindler, K., 2020, AAS, 235, 181.02, Highlights from 125 Years of Lowell Observatory Science: Vera Rubin and the Identification of Dark Matter
    Vera Rubin's identification of dark matter in the Andromeda galaxy using Lowell Observatory's Perkins 72-inch and the KPNO 84-inch telescopes with Kent Ford's image-tube spectrograph represented the culmination and intersection of scientific, technological, collaborative, and managerial interests that spanned the continental United States in the late 1950s and 1960s. Highly sensitive spectroscopic observations were required to detect the redshifts of M31's HII regions, particularly in the outer more tenuous reaches of the great spiral, and adequately generous allocations of telescope time were needed to map out these motions across the whole spatial extent of Andromeda. Because of the constructive spirit of cooperation between scientific and technical staff at Lowell Observatory, Carnegie DTM, Ohio State, USNO, KPNO, Carnegie Pasadena, and other institutions and players, in 1967, driven by an interest in galactic dynamics and the availability of the image-tube spectrograph, Rubin and Ford began a three-year project, dismissed by some colleagues as not worth doing and as overly time-consuming, which ultimately revealed evidence for Fritz Zwicky's conjecture that a significant fraction of gravitationally active matter is not luminous. Rubin pioneered work on some of the most fundamental problems in astrophysics and was an inspiration and supporter to scientists, faculty, and staff at universities and observatories around the world. She made rich contributions to the science and culture at Lowell Observatory where she served on the Board of Advisors for many years and was a colleague and role model to many.
  155. Schindler, K., 2020, AAS, 235, 181.03, The 1894 Lowell Expedition and the Origins of Northern Arizona as Center for Scientific Research
    In 1894, Percival Lowell became fascinated with the possibility of life on Mars and planned to build his own astronomical research facility to carry out studies. He chose Arizona Territory (Arizona didn't achieve statehood until 1912) as site for his observatory and organized an expedition there in order to find an ideal location. He wanted a place removed from eastern U.S. cities, where factory smoke and electric lights blotted out stars and planets. A dry climate and high elevation were also ideal, all characteristics of certain areas in the American Southwest. Lowell himself would not join the expedition. Instead, he hired young astronomer Andrew Douglass to carry out the work. Traveling alone, Douglass performed seeing tests in several locations around the Territory. Based on these observations, Lowell chose Flagstaff as site for his observatory. In looking back at the expedition, Lowell clearly deemed the atmospheric conditions in Flagstaff sufficient for building the observatory there. However, a combination of other factors ensured Flagstaff as the site. Extraordinary community support and politicking by residents certainly helped. Perhaps even a greater factor had to do with timing. Lowell wanted the observatory to be established as quickly as possible. By the time Douglass arrived in Flagstaff, he had been site testing for a month longer than Lowell originally anticipated. The atmospheric conditions in Flagstaff were good, community support was strong, and transportation was adequate, so Lowell, anxious to have telescopes ready for an upcoming Mars opposition, chose Flagstaff. Had Douglass at the time been in another of the locations where conditions were favorable, such as Tombstone, the Observatory quite possibly would have been built there. In any event, Lowell chose Flagstaff and Lowell Observatory became the first permanent scientific institution in Flagstaff. It helped establish the community as a center for scientific research, laying the groundwork for other research facilities in the area such as the Museum of Northern Arizona (1928), U.S. Naval Observatory's Flagstaff Station (1955), U.S. Geological Survey's Astrogeology Branch (1963) and others.
  156. Clark, C., 2020, AAS, 235, 181.04, Elizabeth Williams and the Discovery of Pluto
    In a presentation at MIT in 1902, Percival Lowell postulated the existence of a ninth planet and three years later began searching for what he called "Planet X". The search was twofold, involving mathematically calculating the position of the presumed planet and using telescopes at his observatory in Arizona to photograph likely areas of the sky as suggested by these calculations. He soon hired a young mathematician, Elizabeth Williams, to lead his team of "computers". Williams graduated from MIT in 1903, one of the top mathematics students in her class. When Lowell hired her in 1905, she worked out of his office in Boston. In carrying out the complex calculations necessary for the Planet X search, the talented Williams reportedly wrote in cursive with her right hand and printed with her left. Her calculations were critical to Lowell's predictions of the location of Planet X, as documented in his 1915 publication, Memoirs on a Trans-Neptunian Planet. Lowell died the following year and with him went the Planet X search. In the late 1920s, Lowell Observatory Sole Trustee Roger Putnam and Director VM Slipher decided to recommence the search, acquiring a specially designed astrograph for computing images and hiring 23-year-old farmer and amateur astronomer, Clyde Tombaugh. Looking in the area of sky where Lowell predicted Planet X would be located, Tombaugh discovered Pluto on February 18, 1930. As for Williams, she continued working at Lowell Observatory, moving from Boston to center of operation in Flagstaff in 1919. She married astronomer George Hamilton in 1922, at which time Lowell's widow, Constance, terminated their employment at Lowell. The couple moved to Harvard College Observatory's station in Mandeville, Jamaica and worked side-by-side there until his death in 1935. She then moved to New Hampshire, where she would eventually die penniless. Her name is now a footnote in history, but her efforts as an early astronomical computer stand as a testament to her brilliance and hard work.
  157. van Belle, G., 2020, AAS, 235, 181.05, Interferometry and the Development of NPOI
    Lowell Observatory is a partner in the The Navy Precision Optical Interferometer (NPOI) facility, a long-baseline optical interferometer (LBOI) located at Lowell's Anderson Mesa site near Flagstaff, AZ. NPOI is a modern realization of LBOI efforts, which began in 1919 with the 20-foot beam interferometer that Michelson and Pease bolted to the 100-inch Hooker Telescope. The ensuing colorful century of LBOI, replete with trials and tribulations, visionary and eccentric leaders, and most of all, scientific achievements, is reviewed with an eye towards the promising future of the technique.
  158. Hall, J., 2020, AAS, 235, 181.06, Flagstaff's Dark Sky Heritage
    Flagstaff, Arizona has a 60-year tradition of dark sky preservation, beginning with a 1958 ordinance to ban advertising searchlights. The current ordinance, enacted in 1989, is the most comprehensive in the world; it specifies not only shielding and maximum illumination requirements, but strict control of the emission spectrum via use of low pressure sodium (LPS) lamps. As of the end of May 2019, LPS lamps have been discontinued by lighting manufacturers, so Flagstaff, like many cities worldwide, will be switching its outdoor street lighting system to LEDs. We have spent several years working with City staff to develop what will again be world-leading standards in outdoor illumination, making extensive use of narrow band amber (NBA) and phosphor-converted amber (PCA) LEDs rather than white LEDs. We have already installed NBA and PCA test fixtures in several areas around town, and retrofit of all 3,700 fixtures in Flagstaff should occur in the next 2-5 years. These standards will set the precedent for other applications such as commercial properties and parking lots (pictured below). In this iPoster, I will review the history of dark sky preservation in Flagstaff, the current state of affairs in outdoor lighting, the types of LEDs available, their impact on the night sky, and how Flagstaff will preserve its exceptionally dark sky in the LED era.
  159. Leger, V., Massey, P., Morell, N., et al., 2020, AAS, 235, 204.09, Massive Star Content of OB association Lucke-Hodge 41 (NGC 1910) in the Large Magellanic Cloud
    The Large Magellanic Cloud's (LMC) rich OB association LH41 (NGC 1910) is home to an abundance of O and B type stars, as well S Doradus, the prototypic Luminous Blue Variable, a surprising number of Wolf-Rayet stars, and interesting evolved supergiants. LH41 is the second most active star forming region in the LMC after the famous 30 Doradus, and like its big cousin, is a hotbed for young, massive stars. We have studied this association with HST UV imaging, B- and V-band ground-based photometry, and Magellan 6.5-m optical spectroscopy to determine the massive star content and age of the association. Spectroscopy and modeling using FASTWIND yielded spectral types and effective temperatures for select O and B stars in LH41. This allowed us to apply bolometric corrections to our photometric data and get luminosities and temperatures of the remaining LH41 stars. We eliminated foreground stars using astrometric data from GAIA DR2. The resulting HR Diagram shows a large age spread of O and B type stars, as well as a significant number of evolved supergiants, indicating that LH41 is not strictly coeval. Our findings challenge the current understanding of OB associations as temporary collections of young, hot stars. This work was supported by the National Science Foundation (AST-1852478 and AST-1612874), and by NASA/Space Telescope Science Institute (GO-14707, GO-12940).
  160. Tafla, L., Hunter, D., Elmegreen, B., et al., 2020, AAS, 235, 213.02, Molecular Cloud Structure at Low Metallicity
    Detecting and mapping molecular cloud tracers in gas-rich, low metallicity dwarf irregular galaxies is relevant for the study of star formation in the early universe when metallicities were low. Because of the lower in metallicity it is expected the (giant) molecular clouds to have thicker shells of predominantly H2 and tinier CO cores than GMCs in the Milky Way because there is a commensurate lower abundance of dust to absorb UV light. We identified 47 CO-cores in the Wolf-Lundmark-Melotte (WLM) galaxy from ALMA radio interferometer data using the automated cloud-finding algorithm CLOUDPROPS. We present a study of the CO clouds found in WLM and a review of three other nearby dwarf galaxies with lower abundances than WLM and discuss the upper limits found there. We plotted the CO-cores on FUV and FIR images of WLM to analyze the correlation between CO clouds, HI, and young star clumps in this galaxy. A comparison of the intensity-velocity spectrum of CO-cores and HI is presented. We discuss the relationship between the CO-cores, molecular H2, and young stars. L.T. acknowledges grant AST-1461200 from the National Science Foundation to Northern Arizona University to fund the 2019 REU program and as well as support from the 2019 CAMPARE Scholar program.
  161. Robbins, S., Lisse, C., Singer, K., et al., (including Grundy, W.), 2020, AAS, 235, 220.04, Comets Sourced by KBOs: Comparison of Cometary Size-Frequency Distributions with Outer Solar System Craters
    The outer solar system is thought to be populated by millions of Kuiper Belt Objects (KBOs) ranging in size from the dwarf planets Pluto and Eris (~1000 km radius) down to objects as small as cometary nuclei (~1 km). Today's Jupiter-family comets (JFCs) are likely birthed from scattered KBOs that were once in the trans-Neptunian region. One method to probe the evolution of these bodies is through examination of their size-frequency distribution (SFD), for cometary activity drives changes to the nuclei (e.g., sublimative mass loss and fragmentation) on timescales short compared to dynamical lifetimes. There have been many recent attempts to measure the JFC SFD based on telescopic surveys. Most attempts have derived sizes using optical photometry of sunlight scattered by the nucleus and an assumed albedo, but newer work using Spitzer & WISE infrared photometry can directly measure sizes as thermal emissivities vary little. The IR studies demonstrate cometary SFDs are different from inner solar system asteroid and crater SFDs: Asteroid SFDs follow a reasonably constant power-law at diameters from ~10 km to at least ~10 m. By contrast, the JFC SFD appears to have an inflection point to a shallower SFD slope starting ~1-4 km. However, debiasing these surveys based on observational limitations is difficult, and past authors have tended to propose ad hoc mechanisms for removing small nuclei to reconcile the SFDs. A significant finding from New Horizons mission imagery was that Pluto and Charon impact crater SFDs also have an inflection point to shallower slopes at 10 km ( = ~1 km impactor radius). The result is unambiguous on airless Charon. This is in contrast with previous crater population studies of outer solar system moons which showed a potential small object deficit, but with potential observational biases. Preliminary results of possible impact craters on 2014 MU69 similarly can be interpreted to support a shallower small-object slope. In this work, we present a synthesis: Comparing JFC sizes with crater populations. Taken together, they present strong evidence that there truly is an inflection point in the source KBO population, which has important implications for the evolution of these objects.
  162. Rice, E., Silverman, J., Larson, R., et al., (including Craig, H.), 2020, AAS, 235, 221.01, Broadening Event Horizons through Astronomy on Tap Public Outreach
    Astronomy on Tap (AoT, http://astronomyontap.org) events are a form of public outreach that lowers the barrier to entry for both presenters and the audience by combining science presentations with trivia, games, music, and prizes in a social venue. More than 1000 AoT-affiliated events have been held in over 70 locations worldwide since 2013. AoT events feature one or more presentations given primarily by local professional scientists and graduate students, but also by visiting/international scientists, scientists from fields other than astrophysics, former astronomers working in industries like data science and visualization, humanities professionals with expertise in literature and history, astronauts and other aerospace professionals, undergraduate students, educators, amateur astronomers, writers, artists, musicians, comedians, actors, and other astronomy enthusiasts. The flexible format and content of a typical AoT event is ideal for involving presenters who are not necessarily active as researchers, thus broadening participation in science outreach and expanding networks beyond the astronomy & astrophysics research community. The variety of content, formats, and presenters could also appeal to a broader audience, thus capturing more of the general public into stable orbits within the sphere of influence of science outreach.
  163. Adams, D., 2020, AAS, 235, 221.06, Integrating Cultural Astronomy into Public Outreach Programs
    The modern night sky showcases the remains of cultural interactions that span millennia. Greco-Mesopotamian sky pictures are called by Latin constellation names, but their brightest stars are designated with the letters of the Greek alphabet. Some of these stars also have Greek or Roman proper names, but modern astronomers call most by names derived from Arabic. Of these Arabic star names, some describe Greek astronomy, while others describe indigenous Arabian astronomy. Despite this cultural messiness in the night sky, astronomy outreach programs continue to focus on Greek mythology and a decidedly Western view of the night sky. Taking indigenous (non-Greek) Arabian astronomy as a frame of reference, this presentation offers an alternative to the traditional Greek cultural stories that also addresses core astronomical concepts like precession and proper motion. Other indigenous traditions from outside of Arabia can also be used to similar effect. The application of non-Western astronomical traditions to astronomy outreach programs presents something new to observatory guests that inspires awe and activates curiosity.
  164. Clark, C., van Belle, G., Horch, E., et al., (including von Braun, K.), 2020, AAS, 235, 256.06, The POKEMON Speckle Survey of Nearby M-dwarfs
    We present results from the POKEMON (Pervasive Overview of Kompanions of Every M-dwarf in Our Neighborhood) survey, the most exhaustive stellar multiplicity survey every produced of the objects that comprise over 70% of the stars in our galaxy: the M-dwarfs. We have conducted a volume-limited survey through M9 that inspected, at diffraction-limited resolution, every M-dwarf out to 15pc, with additional brighter targets to 25pc. POKEMON utilized Lowell Observatory's 4.3-m Discovery Channel Telescope with the Differential Speckle Survey Instrument (DSSI @ DCT), along with the NN-Explore Exoplanet Stellar Speckle Imager (NESSI) on the 3.5-m WIYN telescope, to directly image low-mass companions to these M-dwarfs. Given the priority these targets have for exoplanet studies with TESS, and in the future JWST - and the degree to which initially undetected multiplicity has skewed Kepler results - a comprehensive survey of our nearby low-mass neighbors provides a homogeneous, complete catalog of fundamental utility. Prior knowledge of secondary objects - or robust non-detections, as captured by this survey - immediately clarify the nature of exoplanet transit detections from these current and upcoming missions. We report the discovery of 20+ new companions and identify candidate multi-star systems. We establish the most up-to-date M-dwarf multiplicity rate, and obtain sufficient statistics to determine, for the first time, M-dwarf multiplicity as a function of subtype.
  165. Hartman, Z., Lepine, S., Clark, C., et al., (including van Belle, G.), 2020, AAS, 235, 265.03, The Tale of the Lobster: Over-luminous Stars in Wide Binaries and a Search for Higher Order Multiples
    We present a search for higher-order multiples (triples, quadruples, etc.) among K+K and K+M wide binaries identified in the SUPERWIDE all-sky catalog of wide binaries. The SUPERWIDE catalog was assembled from a Bayesian analysis of the high proper motion (> 40 mas/yr) stars in Gaia Data Release 2 (DR2) using their positions, proper motions, and parallaxes. Examining the color-magnitude diagram of the primary and secondary components clearly shows a doubling of the main sequence in the K and early-M dwarf regime, consistent with a normal single star main sequence plus an over-luminous sequence due to some of the components being unresolved binaries. To better identify the over-luminous stars in our wide binaries, we define an over-luminosity factor, which measures the difference between the absolute magnitude of a star and a reference line which runs parallel to the main sequence in the K dwarf region. A "lobster" diagram is then created, which plots the over-luminosity factor of the primary as a function of the over-luminosity factor of the secondary. An examination of this plot reveals that for K+K wide binaries, the higher order multiplicity of the selected sample is at least ~40%. We expand this technique to the lower mass regime (mid-M to late-M) by matching subsets of K+M pairs to the apogee catalog, and by assuming the metallicity of the low-mass secondaries is the same as that of the higher mass primaries. Using the resulting metallicity "tracks", we determine the shape of the main sequence in the M dwarf regime, which allows us to define a proper reference and identify over-luminous components in the M dwarf range as well. To test if our over-luminous components are caused by binarity rather than other potential sources, we crossmatch our sample with TESS, K2 and Kepler to identify eclipsing systems among the over-luminous components and take speckle imaging results from previous observations and the POKEMON survey.
  166. Huls, C., Prato, L., Wasserman, L., et al., 2020, AAS, 235, 272.05, Orbital Parameters for a Young, Low Mass, Spectroscopic Binary Star in Orion
    We present orbital parameters for the young, low-mass, pre-main sequence, double-lined spectroscopic binary, V562 Ori. To measure radial velocities for each of the components in the binary system, we use high-resolution infrared spectra acquired by IGRINS at the Lowell Observatory 4.3m Discovery Channel Telescope. We use a two-dimensional cross-correlation technique, TODCOR, to correlate our observed spectra against standard star templates. The results from this analysis provide radial velocities, spectral types, vsini values, and flux ratios for both components in the binary system. For V562 Ori, the spectral templates that maximized the cross-correlation coefficient were K5 for the primary and K6 for the secondary, with vsini values of 12 km/s and 10 km/s, respectively. By combining the radial velocities from our infrared observations, we are able to determine the orbital parameters and mass ratio for this system. For V562 Ori, we find an orbital period of P = 11.861 0.002 days, and eccentricity of e = 0.075 0.017, a mass ratio of q = 1.008 0.039, and a center-of-mass velocity of 29.24 0.61 km/s. The results shown here not only increase the small sample of PMS spectroscopic binary stars with known orbital elements, but also describes the effectiveness of infrared spectroscopy for the detection of cool secondary stars. We will compare the results obtained with both observed and synthetic template standard star spectra. This research was funded in part by NSF grant AST-1518081 (to L.P.).
  167. Alvarez, C., Kassis, M., Campbell, R., et al., (including Prato, L.), 2020, AAS, 235, 275.11, Keck/MOSFIRE Imaging and Spectroscopy of the Embedded Star Cluster G018.303-0.392
    Embedded Clusters (ECs) are stellar clusters buried in interstellar gas and dust within molecular clouds. Their members are very young forming stars. These stellar nurseries are fundamental to understanding the early stages of star formation. Dynamical interactions between cluster members in these dense environments can lead to the disruption of circumstellar disks and their planetary progeny (Adams and Myers 2001). The application of data mining techniques on large ground-based Galactic IR surveys such as the UKIDSS Galactic Plane Survey (GPS) and the VISTA Variables in the Via Lactea (VVV) survey, and space-based surveys such as the WISE multi-band Atlas, has recently led to the discovery of hundreds of previously unknown embedded-cluster candidates (Solin et al. 2012 and 2014, Camargo et al. 2015 and 2016). Due to the large column densities of interstellar material in these clusters, deep infrared imaging and spectroscopy are ideal to characterize their stellar population. We present Keck/MOSFIRE JHK imaging and K-band multi-object spectroscopy of the region centered on the EC G018.303-0.392, which was included in the list of cluster candidates by Solin et al. (2012). The photometry is used to create color-color and color-magnitude diagrams of the region, which help spotting the reddest sources. K-band spectra show a wide variety to features, including Brackett gamma in absorption and emission, continuum reddening and CO absorption bands. These data will be used to asses the cluster membership of each individual source and to constrain the general properties of the cluster such as distance and age.
  168. Harvison, B., Thomas, C., Hyden, J., et al., (including Moskovitz, N.), 2020, AAS, 235, 277.06, Spectral Analysis of the Agnia Asteroid Family
    Asteroids are considered the remnants of the early solar system and are prime targets of investigation since they can teach us about the history of the solar system and the evolution of the asteroids themselves since their creation. Asteroid families are of particular interest because these groups of objects with similar orbital elements were once part of a larger body that has since been disrupted. Sunshine et al. (2004) used spectral modeling to identify products of partial differentiation in members of the Agnia asteroid family. The study concluded that the Agnia family objects analyzed were most similar to primitive achondrite meteorites. We performed a visible and near-infrared wavelength spectral survey of Agnia family members to enable a follow-up investigation. Our analysis of spectral parameters is based off of the band parameter analyses of Gaffey et al. (1993) and Lucas et al. (2019). Two of the spectral parameters used were the Band 1 and Band 2 centers (B1C and B2C, respectively), the local minimums of the characteristic 1 and 2 micron absorption features with the continuum removed that are indicative of the composition of olivine and pyroxene. The third band parameter, Band Area Ratio (BAR), was the ratio of the area of the 2 micron band to the 1 micron band which is characteristic of the relative abundances of olivine and pyroxene. Gaffey et al. (1993) used the B1C and the BAR to identify compositional S-subtypes which they connected to specific meteorite analogs. Lucas et al. (2019) used the Band 1 and Band 2 Centers to further separate the spectrally similar H ordinary chondrites and acapulcoite-lodranite primitive achondrite meteorites. Further analysis using principal component values calculated by the Bus-DeMeo online classifier (DeMeo et al. 2009) for our asteroid spectra compared to the calculated values of H ordinary chondrites and primitive achondrites provided an additional approach to connecting asteroids and their meteorite analogs. Based on the combination of these analyses, we conclude that members of the Agnia family are most similar to H ordinary chondrites with the possibility that they are primitive achondrite-like.
  169. Hyden, J., Thomas, C., Harvison, B., et al., (including Moskovitz, N.), 2020, AAS, 235, 277.07, Spectral Analysis of the Massalia Asteroid Family
    Asteroid families are remnants of larger parent bodies that were broken apart in a past collisional event. Due to their common origin, asteroids within the same family tend to exhibit similar spectra to one another. We analyzed data from a visible and near-infrared wavelength spectral survey of Massalia family members to study the composition of the family. The Massalia family consists of S-type asteroids that show broad spectral absorption features at 1 and 2 microns. By analyzing these absorption features, we can determine the composition and most likely meteorite analog for the family. We examine these spectral features, by calculating the Band 1 Center, Band 2 Center, and Band Area Ratio (BAR). The Band Centers are the local minima of the bands after the continuum has been removed and the BAR is the ratio of the area of the 2 micron band to the area of the 1 micron band. The Band Centers are indicative of the mineralogy of the olivine and pyroxene of the asteroid. The BAR shows the relative abundance of olivine and pyroxene on the surface of the object. Gaffey et al. (1993) used Band 1 Center and BAR to identify distinct compositional S-subtypes which have been correlated to potential meteorite analogs. We use the Gaffey et al. regions to determine the best meteorite analog for each member of the Massalia family. We also use the Band 1 Center and Band 2 Center to further distinguish between the spectrally similar H ordinary chondrites and, the Acapulcoite and Lodranite primitive achondrites (Lucas et al. 2019). Through conducting this spectral analysis we conclude that the Massalia family asteroids are most similar to H ordinary chondrites.
  170. Holler, B., Grundy, W., Murray, K., et al., (including Mommert, M.), 2020, AAS, 235, 278.06, New Insights into the Eris/Dysnomia System
    The dwarf planet (136199) Eris is known to be the most massive Kuiper Belt Object (KBO) based on the orbit of its large satellite, Dysnomia. At first glance, this system appears to be similar to the Pluto/Charon binary, but there is still much to learn about Eris and Dysnomia. In order to further characterize this system, we used the WFC3 camera onboard the Hubble Space Telescope in early 2018 to observe Dysnomia at roughly evenly spaced intervals over one full orbit. From these data we (1) computed a new orbital fit for Dysnomia, (2) determined the current pole orientation of Eris and characterized its seasons in the present epoch, (3) evaluated the maximum albedo variations across Eris' surface, (4) constructed a rotational light curve of Dysnomia for comparison to ground-based Palomar P60 data of Eris to determine the tidal state of the system, (5) searched for minor satellites, and (6) constrained the Dysnomia-to-Eris mass ratio. Future work will explore the seasonal cycle of Eris over Myr timescales.
  171. Prato, L., Lindstrom, K., Graham, S., et al., 2020, AAS, 235, 308.14, Young Binaries as Laboratories for Disk Evolution: Angularly Resolved Determinations of Stellar and Circumstellar Characteristics
    Detailed properties of the primordial planet-forming disks and of the stars in young multiple systems provide powerful inputs with which to explore the factors controlling the early stages of disk evolution. Because a large fraction, if not most, stars form in pairs, triples, or higher order configurations, characterizing the properties of these systems that dominate disk evolution is key to development of a broad understanding of planet formation. Using adaptive optics fed high-resolution infrared spectroscopy and imaging, we are studying the individual components in systems with separations of a few to a few hundred AU in a sample of 100+ pre-main sequence binaries in the nearby Taurus, Upper Scorpius / Ophiuchus, and TW Hya associations. We present initial results of this survey, including evidence for more rapid disk evolution in lower mass pairs and a paucity of cool primary stars in wide pairs. The advent of the K2 Taurus and Upper Sco / Oph campaigns, as well as the growing wealth of angularly resolved ALMA imaging of disks in these young systems, provide rich, complementary data sets with which to further interpret our results. Ultimately, our spectra and higher-level products of our analysis will be publicly available to the community at http://jumar.lowell.edu/BinaryStars/. Support for this research was provided in part by NSF award AST-1313399 and by NASA Keck KPDA funding.
  172. Lopez-Valdivia, R., Sokal, K., Mace, G., et al., (including Prato, L.), 2020, AAS, 235, 316.04, Stellar parameters of pre-main sequence stars in Taurus and Auriga
    Young Stellar Objects represent the first stages of stellar evolution, and their characterization tests the initial conditions of planetary evolution. Here we present the simultaneous determination of the effective temperature, surface gravity, magnetic field strength, projected rotational velocity and veiling for about one hundred K and M pre-main sequence stars located in the Taurus-Auriga star forming region. We have employed a Markov Chain Monte Carlo approach to fit synthetic models to high-resolution (R ~ 45,000) infrared spectra (1.45 to 2.45 microns), obtained with the Immersion GRating INfrared Spectrometer (IGRINS). The simultaneous approach is critical for disentangling the spectral effects of various parameters. We discuss preliminary results and how they compare with previous, singly-determined physical parameters. This research is made possible by funding from the National Science Foundation grant AST-1908892.
  173. van Belle, G., Moskovitz, N., Patane, S., et al., 2020, AAS, 235, 373.01, Science with Optimast-SCI: New Discovery Frontiers with Sensitive, Millarcsecond Resolution
    The Optimast-SCI (Structurally Connected Interferometry) mission is a NASA-funded SBIR study of the science possibilities enabled by a space-based optical interferometer mission. Optimast-SCI will provide ~2 milliarcsecond spatial resolution with a limiting magnitude of V<12 in a SmallSat package, which even at this small scale is sensitivity performance superior to any ground-based facility by 2-5 magnitudes. A number of scientific opportunities are enabled by this performance. Observation of asteroids can directly measure their sizes, and constrain their albedos; for binary asteroids, orbit mapping can establish masses, and thereby indicate their compositional and structural properties. Observations of young stellar objects will produce results similar to ALMA, but at superior spatial resolution - which corresponds to the terrestrial planet hot-dust regimes, complementary to the gas giant cold-dust regimes of ALMA. At extragalactic distances, Optimast-SCI will have sufficient sensitivity to probe the inner regions of AGNs, constraining the mechanisms that shape the narrow-line region and windy torus. Each one of these areas - and more - are bold new horizons for scientific discovery, from the extreme angular resolution of optical interferometry enabled by space-based sensitivity.
  174. Patane, S., Fagin, M., Riley, D., et al., (including van Belle, G.), 2020, AAS, 235, 373.02, Precision In-Space Manufacturing for Structurally-Connected Interferometry
    In-Space Robotic Manufacturing and Assembly (IRMA) enables novel space mission architectures that broaden the toolkit available to mission planners within the astrophysics community. Equipped with these tools, innovative mission architectures rooted in IRMA offer an alternative approach to achieving science requirements at the forefront of high-spatial resolution astrophysics. The Made In Space Optimast Structurally-Connected Interferometry (SCI) technology will produce a two-aperture system at Sun-Earth L2. Matured via extensive ground testing in a relevant, space-like thermal vacuum environment, Optimast-SCI enables the manufacturing and deployment of structural booms unconstrained by launch loads or volumetric limits of standard vehicle fairings. This foundational additive manufacturing process bypasses limitations of traditional deployable structures by enabling boom designs that reduce parasitic mass. Using its proven in-space additive manufacturing capabilities, the Optimast-SCI hardware drives the efficient packaging of a variable, 1-20 m baseline interferometer to achieve an effective angular resolution in the milliarcsecond regime.
  175. Earle, A., Olkin, C., Stern, S., et al., (including Grundy, W.), 2020, AAS, 235, 419.03, The Color of 2014 MU69
    On January 1, 2019 NASA's New Horizons spacecraft flew close to the Kuiper Belt Object (486958) 2014 MU69 nicknamed "Ultima Thule" (herein MU69). MU69 is a bi-lobed contact binary with an unusual flattened shape. Based on its orbit, MU69 is considered a member of the Cold Classical Kuiper Belt population. This class of objects is thought to be more or less dynamically undisturbed bodies that formed in situ ~4.5 Gyr ago and have since remained at or close to their current, large heliocentric distances. Since MU69 appears to be well preserved, New Horizons' observations of it serve as an opportunity to better understand planetesimal accretion and the earliest stages of planetary formation. In this talk we will focus on the color of MU69's surface, its context as a member of the Kuiper Belt, and the implications its color has for formation scenarios. New Horizons found MU69 to be very red in color (which is consistent with pre-encounter Hubble Telescope observations). Both lobes show basically the same average color. However, subtle color variations exist across the body, for example the less red, higher albedo patches near the "neck" region where the lobes come together. We will explore how these variations correlate with the surface geology of MU69 as well as the insolation and "climate zone" boundaries. We will also consider MU69's color in the broader context of the Kuiper Belt. This red color is consistent with the rest of the Cold Classical Kuiper Belt population, which it is dynamically a member of. Finally, we will discuss the implications MU69's color has for constraining and better understanding its possible formation scenarios.
  176. Umurhan, O., Keane, J., Beyer, R., et al., (including Grundy, W.), 2020, AAS, 235, 419.05, Thermophysical, Gravitational, and Geomorphology Properties of 2014 MU69
    NASA's New Horizons spacecraft imaging of 2014 MU69 on January 1, 2019 revealed a ~16-hr rotating bi-lobed object whose constituents, informally referred to as Ultima and Thule (or collectively "UT"), appear nearly spherical with ~9.5 km and ~7.1 km radii (respectively). Ultima and Thule have similar colors with measured albedos ~ 0.06, indicating that UT is a typical member of the Cold Classical Kuiper Belt class of objects. Detailed image analysis and shape modeling (also presented at this meeting) suggests that UT's obliquity is nearly 99o and Ultima is relatively flattened by comparison to Thule. The surface morphology admits features ranging from small pits, large craters, smooth undifferentiated planes interspersed with scarps possibly derived from sublimation-driven landform evolutionary processes (also discussed at this meeting). Of particular note is the presence of relatively bright materials observed in UT's neck region. Additionally, the onboard radiometer ("REX") observed UT on its backlit side and its beam (4cm wavelength, X-band), containing the entirety of UT's sky projection, measured an approximate brightness temperature of about TB = 29K 5K. However the depth to which the radar beam penetrated UT's near subsurface was not independently measured and therefore requires theoretical modeling. In this talk we survey the gravitational and thermophysical properties of UT derived from detailed global theoretical modeling of the body based on the most recent shape model developed by Beyer and Porter. We place these results into the context of UT's observed features. We calculate the body's geopotential surfaces and local slopes, and based on previous theoretical considerations we conjecture about UT's average density. Further analysis reveals that both of UT's lobes are remarkably well-aligned with their principal axes being nearly parallel. Due to self-shadowing we find that the neck region is on average cooler than the rest of the body despite significant surface re-radiation into the zone. Thule's large deep crater, informally named Maryland, is about 1K warmer than the surrounding regions. We predict that the surface temperature of the unlit side to be about 16K suggesting that the REX beam may have penetrated anywhere from 5-50 cm beneath the surface. We consider these properties in light of UT's possible evolutionary scenarios.
  177. Singer, K., Spencer, J., McKinnon, W., et al., (including Grundy, W.), 2020, AAS, 235, 419.06, Impact craters on 2014 MU69: Implications for Kuiper belt object size-frequency distributions and planetesimal formation
    The size-distribution of small body populations are a signature of solar system formation and evolution processes. Smaller bodies (< ~100 km in diameter) are difficult to observe in the Kuiper belt. The New Horizons flyby of the Pluto-system in July of 2015 provided new data on smaller bodies in the Kuiper belt from observations of impact craters on the surfaces of Pluto and Charon. The new information revealed a previously-unknown deficit of small Kuiper belt objects (KBOs) less than ~1-2 km in diameter (Singer et al., 2019, Science). New Horizons was poised to test this observation 3.5 years later with its next close flyby of the cold classical KBO (486958) 2014 MU69. The images returned by New Horizons in early 2019 show MU69 is only modestly cratered, and potential craters on the surface show a shallow size-frequency distribution (SFD) similar to that of craters on Pluto and Charon (Stern et al. 2019, Science; Singer et al., 2019, EPSC-DPS abstract; Spencer et al. 2019, Science). Both the apparent lack of craters overall, and the shallow SFD slopes, are consistent with a relatively benign collisional environment for MU69 (McKinnon et al., 2019, Science). This deficit of objects smaller than 1 km gives the Kuiper belt population a different shape than the asteroid belt for objects between ~1 km and 200 m in size (the lower end is bound by the smallest impact craters we can see in the New Horizons data). The slope of the Kuiper belt size distribution has a shallow differential power-law slope of approximately -1.8, whereas the Asteroid belt has an average slope closer to -3 in this size range. The shallow slope seen in the Kuiper belt is not representative of a population in traditional collisional equilibrium, and we discuss the implications for formation and evolution of the Kuiper belt and planetesimals in our own solar system, and in other solar systems. Many models assume dust or debris has a collisional size distribution, but the New Horizons data implies there may be more possible outcomes for the size-distribution of evolved planetesimal populations than the traditional collisional equilibrium slope (of approximately -3.5).
  178. Protopapa, S., Olkin, C., Grundy, W., et al., 2020, AAS, 235, 438.03, Titan tholin like materials across the surface of Pluto
    Pluto presents in enhanced visible color images acquired with the New Horizons' Multi-spectral Visible Imaging Camera (MVIC, Reuter et al. 2008) a wide range of colors from vivid red, brown, to yellow colors, highly correlated with Pluto's varied underlying geological structures (Stern et al. 2015; Olkin et al. 2017). The color contrast is less obvious in natural-color images. Tholins, which are the refractory residues obtained from the irradiation of gases and ices containing hydrocarbons (Cruikshank 2005), are thought to be present on the surface of Pluto, serving as coloring agents (e.g., Stern et al. 2018). However, the number of distinct types of tholins on the surface of Pluto, and the processes responsible for their formation and distribution remains subject of investigation. We investigate this problem by means of 1) a multi-wavelength, regionally dependent photometric analysis of Pluto's encounter hemisphere using the color images collected by the Ralph/MVIC instrument on board of New Horizons at four visible wavelengths from 400 nm to 910 nm and 2) analysis, using a multiple-scattering radiative transfer model (Hapke, 2012), of combined MVIC and LEISA (a mapping infrared composition spectrometer covering the wavelength range 1.25-2.50 m) spectra of eastern Cthulhu and Lowell Regio. Cthulhu and Krun Maculae are significantly darker and redder than the rest of the surface. Regions dominated by volatile ices such as the yellow material across Pluto's north pole observed in enhanced color images present single scattering albedos of 0.98 or higher, and almost neutral across the visible wavelength range. This result indicates a very limited contribution of tholin materials on the optically active surfaces in these regions. We use a tholin material with optical constants very similar to that of Titan tholin by Khare et al. (1984) to reproduce the spectral properties of these two regions with such diverse coloration, compositions, morphologies, and ages. Because a single pigment can be used to account for all of Pluto's colors and this is consistent with a Titan tholin like material, we concur with the idea suggested first by Grundy et al. (2018) that Pluto's coloration is the result of photochemical products mostly produced in the atmosphere. Although cosmic rays and ultraviolet photons at wavelengths longer than 145 nm do reach Pluto's surface, and can be expected to drive chemical processing there, the observations of diverse colors do not require different chemical products to be responsible for the colors in different environments.
  179. Lisse, C., Young, L., Cruikshank, D., et al., (including Grundy, W.), 2020, AAS, 235, 438.04, Ices in KBO MU69 and Pluto Implications for Their Formation & Evolution
    The New Horizons (NH) mission flyby of 14 July 2015 verified the presence of an extensive surface ice sheet consisting of CO + N2 ice in Sputnik Planitia, and a near-global covering of layered and structured CH4 ice around the planet. Assuming Pluto was aggregated out of billions of icy planetesimals, the prominence of large amounts of N2 ice is in tension with its ~0.2% vs water abundance found in inner system comets. A similar tension results from the ~1.0 % CH4 vs water in comets. Using the results of the 01 Jan 2019 NH flyby of KBO MU69, we infer new constraints on the icy makeup of the smaller KBOs, which differ substantially from the icy makeup of inner system comets in having abundant amorphous hydrogen-bonded ices like H2O, CH3OH, and (maybe) HCN/H2CO. Here we use this new information and new modeling of the thermodynamic properties of MU69's ices to argue that due to the action of solar insolation, short-lived radioactive isotope decay, micrometeorite bombardment, galactic cosmic rays, passing O/B stars, and nearby supernovae, hypervolatile ices like N2, CO, and CH4 exist today in small icy solar system bodies only as minority species in water ice phases. Only refractory hydrogen-bonded ices should remain after 4.56 Gyrs. Any pure hypervolatile ices that originally condensed "in the dark", while the solar system's midplane was optically thick, were lost within 1 Myr of the time of disk clearing. This implies that Pluto either formed very fast, before the time of disk clearing + 1 Myr, or is completely melted and differentiated through and through, allowing the release of all its minority hypervolatiles from trapped water ice phases and their rise to its surface and atmosphere.
  180. Cale, B., Plavchan, P., Gagne, J., et al., (including von Braun, K.), 2020, AAS, 235, 458.02, Precise Radial Velocities of Cool Low Mass Stars With iSHELL
    We present updates to our program of obtaining precise near infrared (NIR) radial velocities (RVs) with the R ~ 80,000 iSHELL spectrograph on the NASA Infrared Telescope Facility (IRTF) using a methane isotopologue gas cell in the calibration unit. Observing cool low mass stars provides a "Habitable Zone" shortcut through their lower mass, effective temperature, and larger reflex velocities from orbiting bodies. It is advantageous to observe these stars at NIR wavelengths where they emit the bulk of their bolometric luminosity and are most quiescent from rotationally modulated stellar activity. Our novel analysis pipeline extracts RVs by minimizing the RMS of the residuals between the observed spectrum and a forward model, and accounts for the gas cell, tellurics, blaze function, multiple sources of quasi-sinusoidal fringing, and the line spread function of the spectrograph (LSF). The stellar template is derived iteratively using the target observations themselves through averaging barycenter-shifted residuals. With iSHELL we are currently monitoring transiting candidates identified with the NASA TESS mission to determine dynamical masses. We have demonstrated < 3 m/s precision over one-year timescales for the M4 dwarf Barnard's Star, sufficient to detect Neptunes on a wide range of orbits, terrestrial planets on close in orbits, and measure the expected wavelength dependence of stellar activity for young and active stars.
  181. Pendleton, Y., Cruikshank, D., Stern, S., et al., (including Grundy, W.), 2020, IAUS, 350, 91, Kuiper Belt object 2014MU69, Pluto and Phoebe as windows on the composition of the early solar nebula
    The initial chemical composition of a proto-planetary nebula depends upon the degree to which 1) organic and ice components form on dust grains, 2) organic and molecular species form in the gas phase, 3) organics and ices are exchanged between the gas and solid state, and 4) the precursor and newly formed (more complex) materials survive and are modified in the developing planetary system. Infrared and radio observations of star-forming regions reveal that complex chemistry occurs on icy grains, often before stars even form. Additional processing, through the proto-planetary disk (PPD) further modifies most, but not all, of the initial materials. In fact, the modern Solar System still carries a fraction of its interstellar inheritance (Alexander et al. 2017). Here we focus on three examples of small bodies in our Solar System, each containing chemical and dynamical clues to its origin and evolution: the small-cold classical Kuiper Belt object (KBO) 2014 MU69, Pluto, and Saturn's moon, Phoebe. The New Horizons flyby of 2014 MU69 has given the first view of an unaltered body composed of material originally in the solar nebula at ~45 AU. The spectrum of MU69 reveals methanol ice (not commonly found), a possible detection of water ice, and the noteworthy absence of methane ice (Stern et al. 2019). Pluto's internal and surface inventory of volatiles and complex organics, together with active geological processes including cryo-volcanism, indicate a surprising level of activity on a body in the outermost region of the Solar System, and the fluid that emerges from subsurface reservoirs may contain material inherited from the solar nebula (Cruikshank et al. 2019). Meanwhile, Saturn's captured moon, Phoebe, carries high D/H in H2O (Clark et al. 2019) and complex organics (Cruikshank et al. 2008), both consistent with its formation in, and inheritance from, the outer region of the solar nebula. Together, these objects provide windows on the origin and evolution of our Solar System and constraints to be considered in future chemical and physical models of PPDs.
  182. Kavanagh, R., Vidotto, A., O Fionnagain, D., et al., (including Llama, J.), 2020, IAUS, 354, 305, Tuning in to the radio environment of HD189733b
    The hot Jupiter HD189733b is expected to be a source of strong radio emission, due to its close proximity to its magnetically active host star. Here, we model the stellar wind of its host star, based on reconstructed surface stellar magnetic field maps. We use the local stellar wind properties at the planetary orbit obtained from our models to compute the expected radio emission from the planet. Our findings show that the planet emits with a peak flux density within the detection capabilities of LOFAR. However, due to absorption by the stellar wind itself, this emission may be attenuated significantly. We show that the best time to observe the system is when the planet is near primary transit of the host star, as the attenuation from the stellar wind is lowest in this region.
  183. 182 publications and 3163 citations in 2020.

182 publications and 3163 citations total.