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Research involving Lowell Observatory staff 2020
(Articles and chapters)

This is a work ever in progress.

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Years: 2020 Bottom

    2020

  1. dal Ponte, M., Santiago, B., Carnero Rosell, A., Burningham, B., Yanny, B., Marshall, J., Bechtol, K., Martini, P., Li, T., De Paris, L., Abbott, T., Aguena, M., Allam, S., Avila, S., Bertin, E., Bhargava, S., Brooks, D., Buckley-Geer, E., Kind, M., Carretero, J., da Costa, L., De Vicente, J., Diehl, H., Doel, P., Eifler, T., Everett, S., Flaugher, B., Fosalba, P., Frieman, J., Garcia-Bellido, J., Gaztanaga, E., Gerdes, D., Gruen, D., Gruendl, R., Gschwend, J., Gutierrez, G., Hinton, S., Hollowood, D., Honscheid, K., James, D., Kuehn, K., Kuropatkin, N., Maia, M., March, M., Menanteau, F., Miquel, R., Palmese, A., Paz-Chinchon, F., Plazas, A., Sanchez, E., Scarpine, V., Serrano, S., Sevilla-Noarbe, I., Smith, M., Suchyta, E., Swanson, M., Tarle, G., Thomas, D., Varga, T., Walker, A., DES Collaboration, 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., Holgado, A., Guo, H., Gruendl, R., Morganson, E., Shen, Y., Zhang, K., Abbott, T., Aguena, M., Allam, S., Avila, S., Bertin, E., Bhargava, S., Brooks, D., Burke, D., Carnero Rosell, A., Carollo, D., Carrasco Kind, M., Carretero, J., Costanzi, M., da Costa, L., Davis, T., De Vicente, J., Desai, S., Diehl, H., Doel, P., Everett, S., Flaugher, B., Friedel, D., Frieman, J., Garcia-Bellido, J., Gaztanaga, E., Glazebrook, K., Gruen, D., Gutierrez, G., Hinton, S., Hollowood, D., James, D., Kim, A., Kuehn, K., Kuropatkin, N., Lewis, G., Lidman, C., Lima, M., Maia, M., March, M., Marshall, J., Menanteau, F., Miquel, R., Palmese, A., Paz-Chinchon, F., Plazas, A., Sanchez, E., Schubnell, M., Serrano, S., Sevilla-Noarbe, I., Smith, M., Suchyta, E., Swanson, M., Tarle, G., Tucker, B., Norbert Varga, T., Walker, A., 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. Kingsley, J., Strittmatter, P., Gonzales, K., Connors, T., Kingsley, B., Jannuzi, B., Yoshii, Y., Minezaki, T., 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.
  4. Cornelius, F., Sweaton, M., Hardesty, B., 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.
  5. Kuehn, K., Kuhlmann, S., Ellis, S., Stern, N., Liu, P., Caldwell-Meurer, H., Spinka, H., Underwood, D., Kehoe, R., 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!
  6. Neugent, K., Levesque, E., Massey, P., Morrell, N., Drout, M., 2020, ApJ, 905, 83, Erratum: "The Red Supergiant Binary Fraction of the Large Magellanic Cloud" (2020, ApJ, 900, 118)
    No abstract found.
  7. Scowen, P., Ardila, D., Jensen, L., Gamaunt, J., Nikzad, S., Jewell, A., Austin, J., Beasley, M., Shkolnik, E., Barman, T., Bowman, J., Gorjian, V., Gregory, D., Jacobs, D., Llama, J., Knapp, M., Meadows, V., Peacock, S., Ramiaramanantsoa, T., Swain, M., Vedder, P., Whelan, L., Zellem, R., 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.
  8. van Belle, G., Clark, J., Armstrong, J., Baines, E., Martinez, T., Restaino, S., Schmitt, H., Jorgensen, A., Mozurkewich, D., 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.
  9. Clark, C., van Belle, G., Horch, E., Trilling, D., 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.
  10. van Belle, G., Hillsberry, D., Kloske, J., Kugler, J., Patane, S., Paul-Gin, N., Piness, J., Riley, D., Schomer, J., Snyder, M., Tobiassen, T., 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.
  11. Pandey, S., Krause, E., Jain, B., MacCrann, N., Blazek, J., Crocce, M., DeRose, J., Fang, X., Ferrero, I., Friedrich, O., Aguena, M., Allam, S., Annis, J., Avila, S., Bernstein, G., Brooks, D., Burke, D., Carnero Rosell, A., Carrasco Kind, M., Carretero, J., Costanzi, M., da Costa, L., De Vicente, J., Desai, S., Elvin-Poole, J., Everett, S., Fosalba, P., Frieman, J., Garcia-Bellido, J., Gruen, D., Gruendl, R., Gschwend, J., Gutierrez, G., Honscheid, K., Kuehn, K., Kuropatkin, N., Maia, M., Marshall, J., Menanteau, F., Miquel, R., Palmese, A., Paz-Chinchon, F., Plazas, A., Roodman, A., Sanchez, E., Scarpine, V., Schubnell, M., Serrano, S., Sevilla-Noarbe, I., Smith, M., Soares-Santos, M., Suchyta, E., Swanson, M., Tarle, G., Weller, J., 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.
  12. Hinkle, K., Lebzelter, T., Fekel, F., Straniero, O., Joyce, R., Prato, L., Karnath, N., Habel, N., 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.
  13. Fedorets, G., Micheli, M., Jedicke, R., Naidu, S., Farnocchia, D., Granvik, M., Moskovitz, N., Schwamb, M., Weryk, R., Wierzchos, K., Christensen, E., Pruyne, T., Bottke, W., Ye, Q., Wainscoat, R., Devogele, M., Buchanan, L., Djupvik, A., Faes, D., Fohring, D., Roediger, J., Seccull, T., Smith, A., 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.
  14. Smith, M., D'Andrea, C., Sullivan, M., Moller, A., Nichol, R., Thomas, R., Kim, A., Sako, M., Castander, F., Filippenko, A., Foley, R., Galbany, L., Gonzalez-Gaitan, S., Kasai, E., Kirshner, R., Lidman, C., Scolnic, D., Brout, D., Davis, T., Gupta, R., Hinton, S., Kessler, R., Lasker, J., Macaulay, E., Wolf, R., Zhang, B., Asorey, J., Avelino, A., Bassett, B., Calcino, J., Carollo, D., Casas, R., Challis, P., Childress, M., Clocchiatti, A., Crawford, S., Frohmaier, C., Glazebrook, K., Goldstein, D., Graham, M., Hoormann, J., Kuehn, K., Lewis, G., Mandel, K., Morganson, E., Muthukrishna, D., Nugent, P., Pan, Y., Pursiainen, M., Sharp, R., Sommer, N., Swann, E., Thomas, B., Tucker, B., Uddin, S., Wiseman, P., Zheng, W., Abbott, T., Annis, J., Avila, S., Bechtol, K., Bernstein, G., Bertin, E., Brooks, D., Burke, D., Carnero Rosell, A., Carrasco Kind, M., Carretero, J., Cunha, C., da Costa, L., Davis, C., De Vicente, J., Diehl, H., Eifler, T., Estrada, J., Frieman, J., Garcia-Bellido, J., Gaztanaga, E., Gerdes, D., Gruen, D., Gruendl, R., Gschwend, J., Gutierrez, G., Hartley, W., Hollowood, D., Honscheid, K., Hoyle, B., James, D., Johnson, M., Johnson, M., Kuropatkin, N., Li, T., Lima, M., Maia, M., March, M., Marshall, J., Martini, P., Menanteau, F., Miller, C., Miquel, R., Neilsen, E., Ogando, R., Plazas, A., Romer, A., Sanchez, E., Scarpine, V., Schubnell, M., Serrano, S., Sevilla-Noarbe, I., Soares-Santos, M., Sobreira, F., Suchyta, E., Tarle, G., Tucker, D., Wester, W., 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.
  15. Oszkiewicz, D., Troianskyi, V., Fohring, D., Galad, A., Kwiatkowski, T., Marciniak, A., Skiff, B., Geier, S., Borczyk, W., Moskovitz, N., Kankiewicz, P., Gajdos, S., Vilagi, J., Polcic, L., Kluwak, T., Wilawer, E., Kashuba, V., Udovichenko, S., Keir, L., Kaminski, K., 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.
  16. Pereira, M., Palmese, A., Varga, T., McClintock, T., Soares-Santos, M., Burgad, J., Annis, J., Farahi, A., Lin, H., Choi, A., DeRose, J., Esteves, J., Gatti, M., Gruen, D., Hartley, W., Hoyle, B., Jeltema, T., MacCrann, N., Roodman, A., Sanchez, C., Shin, T., von der Linden, A., Zuntz, J., Abbott, T., Aguena, M., Avila, S., Bertin, E., Bhargava, S., Bridle, S., Brooks, D., Burke, D., Carnero Rosell, A., Carrasco Kind, M., Carretero, J., Costanzi, M., da Costa, L., Desai, S., Diehl, H., Dietrich, J., Doel, P., Estrada, J., Everett, S., Flaugher, B., Fosalba, P., Frieman, J., Garcia-Bellido, J., Gaztanaga, E., Gerdes, D., Gruendl, R., Gschwend, J., Gutierrez, G., Hinton, S., Hollowood, D., Honscheid, K., James, D., Kuehn, K., Kuropatkin, N., Lahav, O., Lima, M., Maia, M., March, M., Marshall, J., Melchior, P., Menanteau, F., Miquel, R., Ogando, R., Paz-Chinchon, F., Plazas, A., Romer, A., Sanchez, E., Scarpine, V., Schubnell, M., Serrano, S., Sevilla-Noarbe, I., Smith, M., Suchyta, E., Swanson, M., Tarle, G., Wechsler, R., Weller, J., Zhang, Y., Zhang, Y., DES Collaboration, 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.
  17. Buckley-Geer, E., Lin, H., Rusu, C., Poh, J., Palmese, A., Agnello, A., Christensen, L., Frieman, J., Shajib, A., Treu, T., Collett, T., Birrer, S., Anguita, T., Fassnacht, C., Meylan, G., Mukherjee, S., Wong, K., Aguena, M., Allam, S., Avila, S., Bertin, E., Bhargava, S., Brooks, D., Carnero Rosell, A., Carrasco Kind, M., Carretero, J., Castander, F., Costanzi, M., da Costa, L., De Vicente, J., Desai, S., Diehl, H., Doel, P., Eifler, T., Everett, S., Flaugher, B., Fosalba, P., Garcia-Bellido, J., Gaztanaga, E., Gruen, D., Gruendl, R., Gschwend, J., Gutierrez, G., Hinton, S., Honscheid, K., James, D., Kuehn, K., Kuropatkin, N., Maia, M., Marshall, J., Melchior, P., Menanteau, F., Miquel, R., Ogando, R., Paz-Chinchon, F., Plazas, A., Sanchez, E., Scarpine, V., Schubnell, M., Serrano, S., Sevilla-Noarbe, I., Smith, M., Soares-Santos, M., Suchyta, E., Swanson, M., Tarle, G., Tucker, D., Varga, T., DES Collaboration, 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.
  18. Gatti, M., Chang, C., Friedrich, O., Jain, B., Bacon, D., Crocce, M., DeRose, J., Ferrero, I., Fosalba, P., Gaztanaga, E., Gruen, D., Harrison, I., Jeffrey, N., MacCrann, N., McClintock, T., Secco, L., Whiteway, L., Abbott, T., Allam, S., Annis, J., Avila, S., Brooks, D., Buckley-Geer, E., Burke, D., Carnero Rosell, A., Carrasco Kind, M., Carretero, J., Cawthon, R., da Costa, L., De Vicente, J., Desai, S., Diehl, H., Doel, P., Eifler, T., Estrada, J., Everett, S., Evrard, A., Frieman, J., Garcia-Bellido, J., Gerdes, D., Gruendl, R., Gschwend, J., Gutierrez, G., James, D., Johnson, M., Krause, E., Kuehn, K., Lima, M., Maia, M., March, M., Marshall, J., Melchior, P., Menanteau, F., Miquel, R., Palmese, A., Paz-Chinchon, F., Plazas, A., Sanchez, C., Sanchez, E., Scarpine, V., Schubnell, M., Santiago, S., Sevilla-Noarbe, I., Smith, M., Soares-Santos, M., Suchyta, E., Swanson, M., Tarle, G., Thomas, D., Troxel, M., Zuntz, J., Zuntz, J., DES Collaboration, 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.
  19. Garcia, A., Morgan, R., Herner, K., Palmese, A., Soares-Santos, M., Annis, J., Brout, D., Vivas, A., Drlica-Wagner, A., Santana-Silva, L., Tucker, D., Allam, S., Wiesner, M., Garcia-Bellido, J., Gill, M., Sako, M., Kessler, R., Davis, T., Scolnic, D., Casares, J., Chen, H., Conselice, C., Cooke, J., Doctor, Z., Foley, R., Horvath, J., Howell, D., Kilpatrick, C., Lidman, C., Olivares E., F., Paz-Chinchon, F., Pineda-G., J., Quirola-Vasquez, J., Rest, A., Sherman, N., Abbott, T., Aguena, M., Avila, S., Bertin, E., Bhargava, S., Brooks, D., Burke, D., Carnero Rosell, A., Carrasco Kind, M., Carretero, J., Costanzi, M., da Costa, L., Desai, S., Diehl, H., Dietrich, J., Doel, P., Everett, S., Flaugher, B., Fosalba, P., Friedel, D., Frieman, J., Gaztanaga, E., Gerdes, D., Gruen, D., Gruendl, R., Gschwend, J., Gutierrez, G., Hinton, S., Hollowood, D., Honscheid, K., James, D., Kuehn, K., Kuropatkin, N., Lahav, O., Lima, M., Maia, M., March, M., Marshall, J., Menanteau, F., Miquel, R., Ogando, R., Plazas, A., Romer, A., Roodman, A., Sanchez, E., Scarpine, V., Schubnell, M., Serrano, S., Sevilla-Noarbe, I., Smith, M., Suchyta, E., Swanson, M., Tarle, G., Thomas, D., Varga, T., Walker, A., Weller, J., DES Collaboration, 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.
  20. Wiseman, P., Pursiainen, M., Childress, M., Swann, E., Smith, M., Galbany, L., Lidman, C., Davis, T., Gutierrez, C., Moller, A., Thomas, B., Frohmaier, C., Foley, R., Hinton, S., Kelsey, L., Kessler, R., Lewis, G., Sako, M., Scolnic, D., Sullivan, M., Vincenzi, M., Abbott, T., Aguena, M., Allam, S., Annis, J., Bertin, E., Bhargava, S., Brooks, D., Burke, D., Carnero Rosell, A., Carollo, D., Carrasco Kind, M., Carretero, J., Costanzi, M., da Costa, L., Diehl, H., Doel, P., Everett, S., Fosalba, P., Frieman, J., Garcia-Bellido, J., Gaztanaga, E., Glazebrook, K., Gruen, D., Gruendl, R., Gschwend, J., Gutierrez, G., Hollowood, D., Honscheid, K., James, D., Kuehn, K., Kuropatkin, N., Lima, M., Maia, M., Marshall, J., Martini, P., Menanteau, F., Miquel, R., Palmese, A., Paz-Chinchon, F., Plazas, A., Romer, A., Sanchez, E., Scarpine, V., Schubnell, M., Serrano, S., Sevilla-Noarbe, I., Sommer, N., Suchyta, E., Swanson, M., Tarle, G., Tucker, B., Tucker, D., Varga, T., Walker, A., Walker, A., (DES Collaboration), 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.
  21. Grandis, S., Klein, M., Mohr, J., Bocquet, S., Paulus, M., Abbott, T., Aguena, M., Allam, S., Annis, J., Benson, B., Bertin, E., Bhargava, S., Brooks, D., Burke, D., Carnero Rosell, A., Carrasco Kind, M., Carretero, J., Capasso, R., Costanzi, M., da Costa, L., De Vicente, J., Desai, S., Dietrich, J., Doel, P., Eifler, T., Evrard, A., Flaugher, B., Fosalba, P., Frieman, J., Garcia-Bellido, J., Gaztanaga, E., Gerdes, D., Gruen, D., Gruendl, R., Gschwend, J., Gutierrez, G., Hartley, W., Hinton, S., Hollowood, D., Honscheid, K., James, D., Jeltema, T., Kuehn, K., Kuropatkin, N., Lima, M., Maia, M., Marshall, J., Melchior, P., Menanteau, F., Miquel, R., Ogando, R., Palmese, A., Paz-Chinchon, F., Plazas, A., Romer, A., Roodman, A., Sanchez, E., Saro, A., Scarpine, V., Schubnell, M., Serrano, S., Sheldon, E., Smith, M., Stark, A., Suchyta, E., Swanson, M., Tarle, G., Thomas, D., Tucker, D., Varga, T., Weller, J., Wilkinson, R., 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.
  22. Jones, T., Kim, J., Dowell, C., Morris, M., Pineda, J., Benford, D., Berthoud, M., Chuss, D., Dale, D., Fissel, L., Goldsmith, P., Hamilton, R., Hanany, S., Harper, D., Henning, T., Lazarian, A., Looney, L., Michail, J., Novak, G., Santos, F., Sheth, K., Siah, J., Stacey, G., Staguhn, J., Stephens, I., Tassis, K., Trinh, C., Vaillancourt, J., Ward-Thompson, D., Werner, M., Wollack, E., Zweibel, E., HAWC+ Science Team, 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.
  23. Ji, A., Li, T., Hansen, T., Casey, A., Koposov, S., Pace, A., Mackey, D., Lewis, G., Simpson, J., Bland-Hawthorn, J., Cullinane, L., Da Costa, G., Hattori, K., Martell, S., Kuehn, K., Erkal, D., Shipp, N., Wan, Z., Zucker, D., 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.
  24. Smith, E., Logsdon, S., McLean, I., Fletcher, E., Vacca, W., Becklin, E., Shenoy, S., Savage, M., 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.
  25. Cartwright, R., Nordheim, T., Cruikshank, D., Hand, K., Roser, J., Grundy, W., Beddingfield, C., Emery, J., 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.
  26. Leung, Y., Zhang, Y., Yanny, B., Herner, K., Annis, J., Palmese, A., Sampaio-Santos, H., Strazzullo, V., Aguena, M., Allam, S., Avila, S., Bertin, E., Bhargava, S., Brooks, D., Burke, D., Carnero Rosell, A., Carrasco Kind, M., Carretero, J., Costanzi, M., da Costa, L., Desai, S., Diehl, H., Doel, P., Eifler, T., Everett, S., Flaugher, B., Frieman, J., Garcia-Bellido, J., Gaztanaga, E., Gruen, D., Gruendl, R., Gschwend, J., Gutierrez, G., Honscheid, K., James, D., Kim, A., Kuehn, K., Kuropatkin, N., Lima, M., Maia, M., Miquel, R., Ogando, R., Paz-Chinchon, F., Plazas, A., Romer, A., Roodman, A., Rykoff, E., Sanchez, E., Scarpine, V., Schubnell, M., Serrano, S., Sevilla-Noarbe, I., Smith, M., Suchyta, E., Swanson, M., Varga, T., 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.
  27. Bertrand, T., Forget, F., Schmitt, B., White, O., 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.
  28. Dorn-Wallenstein, T., Levesque, E., Neugent, K., Davenport, J., Morris, B., Gootkin, K., 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.
  29. 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.
  30. Eckert, K., Bernstein, G., Amara, A., Amon, A., Choi, A., Everett, S., Gruen, D., Gruendl, R., Huff, E., Kuropatkin, N., Roodman, A., Sheldon, E., Yanny, B., Zhang, Y., Abbott, T., Aguena, M., Avila, S., Bechtol, K., Brooks, D., Burke, D., Carnero Rosell, A., Carrasco Kind, M., Carretero, J., Costanzi, M., da Costa, L., De Vicente, J., Desai, S., Diehl, H., Dietrich, J., Eifler, T., Evrard, A., Flaugher, B., Frieman, J., Garcia-Bellido, J., Gaztanaga, E., Gschwend, J., Gutierrez, G., Hartley, W., Hollowood, D., Honscheid, K., James, D., Kron, R., Kuehn, K., Maia, M., Marshall, J., Melchior, P., Menanteau, F., Miquel, R., Ogando, R., Palmese, A., Paz-Chinchon, F., Plazas, A., Romer, A., Sanchez, E., Scarpine, V., Serrano, S., Sevilla-Noarbe, I., Smith, M., Soares-Santos, M., Suchyta, E., Swanson, M., Tarle, G., Thomas, D., Varga, T., Walker, A., Wester, W., Wilkinson, R., Zuntz, J., Zuntz, J., (The DES Collaboration), 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.
  31. Zhang, H., Smith, R., Oh, S., Paudel, S., Duc, P., Boselli, A., Cote, P., Ferrarese, L., Gao, Y., Hunter, D., Puzia, T., Peng, E., Rong, Y., Shin, J., Zhao, Y., 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.
  32. Morgan, R., Soares-Santos, M., Annis, J., Herner, K., Garcia, A., Palmese, A., Drlica-Wagner, A., Kessler, R., Garcia-Bellido, J., Bachmann, T., Sherman, N., Allam, S., Bechtol, K., Bom, C., Brout, D., Butler, R., Butner, M., Cartier, R., Chen, H., Conselice, C., Cook, E., Davis, T., Doctor, Z., Farr, B., Figueiredo, A., Finley, D., Foley, R., Galarza, J., Gill, M., Gruendl, R., Holz, D., Kuropatkin, N., Lidman, C., Lin, H., Malik, U., Mann, A., Marriner, J., Marshall, J., Martinez-Vazquez, C., Meza, N., Neilsen, E., Nicolaou, C., Olivares E., F., Paz-Chinchon, F., Points, S., Quirola-Vasquez, J., Rodriguez, O., Sako, M., Scolnic, D., Smith, M., Sobreira, F., Tucker, D., Vivas, A., Wiesner, M., Wood, M., Yanny, B., Zenteno, A., Abbott, T., Aguena, M., Avila, S., Bertin, E., Bhargava, S., Brooks, D., Burke, D., Rosell, A., Kind, M., Carretero, J., Costa, L., Costanzi, M., De Vicente, J., Desai, S., Diehl, H., Doel, P., Eifler, T., Everett, S., Flaugher, B., Frieman, J., Gaztanaga, E., Gerdes, D., Gruen, D., Gschwend, J., Gutierrez, G., Hartley, W., Hinton, S., Hollowood, D., Honscheid, K., James, D., Kuehn, K., Lahav, O., Lima, M., Maia, M., March, M., Miquel, R., Ogando, R., Plazas, A., Roodman, A., Sanchez, E., Scarpine, V., Schubnell, M., Serrano, S., Sevilla-Noarbe, I., Suchyta, E., Tarle, G., 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.
  33. Steckloff, J., Soderblom, J., Farnsworth, K., Chevrier, V., Hanley, J., Soto, A., Groven, J., Grundy, W., Pearce, L., Tegler, S., Engle, A., 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.
  34. Leiva, R., Buie, M., Keller, J., Wasserman, L., Kavelaars, J., Bridges, T., Haley, S., Strauss, R., Wilde, E., Weryk, R., Kervella, P., Baker, R., Bock, S., Conway, K., Cota, J., Estes, J., Garcia, M., Kehrli, M., McCandless, A., McCandless, K., Self, E., Settlemire, C., Swanson, D., Thompson, D., Wise, J., 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.
  35. Neugent, K., Levesque, E., Massey, P., Morrell, N., Drout, M., 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%.
  36. Palmese, A., deVicente, J., Pereira, M., Annis, J., Hartley, W., Herner, K., Soares-Santos, M., Crocce, M., Huterer, D., Magana Hernandez, I., Garcia, A., Garcia-Bellido, J., Gschwend, J., Holz, D., Kessler, R., Lahav, O., Morgan, R., Nicolaou, C., Conselice, C., Foley, R., Gill, M., Abbott, T., Aguena, M., Allam, S., Avila, S., Bechtol, K., Bertin, E., Bhargava, S., Brooks, D., Buckley-Geer, E., Burke, D., Carrasco Kind, M., Carretero, J., Castander, F., Chang, C., Costanzi, M., da Costa, L., Davis, T., Desai, S., Diehl, H., Doel, P., Drlica-Wagner, A., Estrada, J., Everett, S., Evrard, A., Fernandez, E., Finley, D., Flaugher, B., Fosalba, P., Frieman, J., Gaztanaga, E., Gerdes, D., Gruen, D., Gruendl, R., Gutierrez, G., Hinton, S., Hollowood, D., Honscheid, K., James, D., Kent, S., Krause, E., Kuehn, K., Lin, H., Maia, M., March, M., Marshall, J., Melchior, P., Menanteau, F., Miquel, R., Ogando, R., Paz-Chinchon, F., Plazas, A., Roodman, A., Sako, M., Sanchez, E., Scarpine, V., Schubnell, M., Serrano, S., Sevilla-Noarbe, I., Smith, J., Smith, M., Suchyta, E., Tarle, G., Troxel, M., Tucker, D., Walker, A., Wester, W., Wilkinson, R., Zuntz, J., DES Collaboration, 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.
  37. Noll, K., Brown, M., Weaver, H., Grundy, W., Porter, S., Buie, M., Levison, H., Olkin, C., Spencer, J., Marchi, S., Statler, T., 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.
  38. Pang, X., Li, Y., Tang, S., Pasquato, M., Kouwenhoven, M., 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.
  39. Guo, H., Burke, C., Liu, X., Phadke, K., Zhang, K., Chen, Y., Gruendl, R., Lidman, C., Shen, Y., Morganson, E., Aguena, M., Allam, S., Avila, S., Bertin, E., Brooks, D., Rosell, A., Carollo, D., Kind, M., Costanzi, M., da Costa, L., De Vicente, J., Desai, S., Doel, P., Eifler, T., Everett, S., Garcia-Bellido, J., Gaztanaga, E., Gerdes, D., Gruen, D., Gschwend, J., Gutierrez, G., Hinton, S., Hollowood, D., Honscheid, K., James, D., Kuehn, K., Lima, M., Maia, M., Menanteau, F., Miquel, R., Moller, A., Ogando, R., Palmese, A., Paz-Chinchon, F., Plazas, A., Romer, A., Roodman, A., Sanchez, E., Scarpine, V., Schubnell, M., Serrano, S., Smith, M., Soares-Santos, M., Sommer, N., Suchyta, E., Swanson, M., Tarle, G., Tucker, B., Varga, T., (DES Collaboration), 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.
  40. Macaulay, E., Bacon, D., Nichol, R., Davis, T., Elvin-Poole, J., Brout, D., Carollo, D., Glazebrook, K., Hinton, S., Lewis, G., Lidman, C., Moller, A., Sako, M., Scolnic, D., Smith, M., Sommer, N., Tucker, B., Abbott, T., Aguena, M., Annis, J., Avila, S., Bertin, E., Bhargava, S., Brooks, D., Burke, D., Carnero Rosell, A., Carrasco Kind, M., Carretero, J., Castander, F., Costanzi, M., da Costa, L., Desai, S., Diehl, H., Doel, P., Flaugher, B., Foley, R., Garcia-Bellido, J., Gaztanaga, E., Gerdes, D., Gruen, D., Gruendl, R., Gschwend, J., Gutierrez, G., Hollowood, D., Honscheid, K., Huterer, D., James, D., Kuehn, K., Kuropatkin, N., Lahav, O., Lima, M., Maia, M., Marshall, J., Melchior, P., Menanteau, F., Miquel, R., Palmese, A., Plazas, A., Romer, A., Roodman, A., Sanchez, E., Scarpine, V., Schubnell, M., Serrano, S., Sevilla-Noarbe, I., Soares-Santos, M., Suchyta, E., Swanson, M., Tarle, G., Varga, T., Walker, A., Weller, J., DES Collaboration, 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.
  41. Hartley, W., Chang, C., Samani, S., Carnero Rosell, A., Davis, T., Hoyle, B., Gruen, D., Asorey, J., Gschwend, J., Lidman, C., Kuehn, K., King, A., Rau, M., Wechsler, R., DeRose, J., Hinton, S., Whiteway, L., Abbott, T., Aguena, M., Allam, S., Annis, J., Avila, S., Bernstein, G., Bertin, E., Bridle, S., Brooks, D., Burke, D., Carrasco Kind, M., Carretero, J., Castander, F., Cawthon, R., Costanzi, M., da Costa, L., Desai, S., Diehl, H., Dietrich, J., Flaugher, B., Fosalba, P., Frieman, J., Garcia-Bellido, J., Gaztanaga, E., Gerdes, D., Gruendl, R., Gutierrez, G., Hollowood, D., Honscheid, K., James, D., Kent, S., Krause, E., Kuropatkin, N., Lahav, O., Lima, M., Maia, M., Marshall, J., Melchior, P., Menanteau, F., Miquel, R., Ogando, R., Palmese, A., Paz-Chinchon, F., Plazas, A., Roodman, A., Rykoff, E., Sanchez, E., Scarpine, V., Schubnell, M., Serrano, S., Sevilla-Noarbe, I., Smith, M., Soares-Santos, M., Suchyta, E., Tarle, G., Troxel, M., Tucker, D., Varga, T., Weller, J., Wilkinson, R., DES Collaboration, 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.
  42. van Belle, G., Collins, M., Guzman, G., 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.
  43. Brewer, J., Fischer, D., Blackman, R., Cabot, S., Davis, A., Laughlin, G., Leet, C., Ong, J., Petersburg, R., Szymkowiak, A., Zhao, L., Henry, G., 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.
  44. de Jaeger, T., Galbany, L., Gonzalez-Gaitan, S., Kessler, R., Filippenko, A., Forster, F., Hamuy, M., Brown, P., Davis, T., Gutierrez, C., Inserra, C., Lewis, G., Moller, A., Scolnic, D., Smith, M., Brout, D., Carollo, D., Foley, R., Glazebrook, K., Hinton, S., Macaulay, E., Nichol, B., Sako, M., Sommer, N., Tucker, B., Abbott, T., Aguena, M., Allam, S., Annis, J., Avila, S., Bertin, E., Bhargava, S., Brooks, D., Burke, D., Carnero Rosell, A., Carrasco Kind, M., Carretero, J., Costanzi, M., Crocce, M., da Costa, L., De Vicente, J., Desai, S., Diehl, H., Doel, P., Drlica-Wagner, A., Eifler, T., Estrada, J., Everett, S., Flaugher, B., Fosalba, P., Frieman, J., Garcia-Bellido, J., Gaztanaga, E., Gruen, D., Gruendl, R., Gschwend, J., Gutierrez, G., Hartley, W., Hollowood, D., Honscheid, K., James, D., Kuehn, K., Kuropatkin, N., Li, T., Lima, M., Maia, M., Menanteau, F., Miquel, R., Palmese, A., Paz-Chinchon, F., Plazas, A., Romer, A., Roodman, A., Sanchez, E., Scarpine, V., Schubnell, M., Serrano, S., Sevilla-Noarbe, I., Soares-Santos, M., Suchyta, E., Swanson, M., Tarle, G., Thomas, D., Tucker, D., Varga, T., Walker, A., Weller, J., Wilkinson, R., DES Collaboration, 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.
  45. Wiseman, P., Smith, M., Childress, M., Kelsey, L., Moller, A., Gupta, R., Swann, E., Angus, C., Brout, D., Davis, T., Foley, R., Frohmaier, C., Galbany, L., Gutierrez, C., Inserra, C., Kessler, R., Lewis, G., Lidman, C., Macaulay, E., Nichol, R., Pursiainen, M., Sako, M., Scolnic, D., Sommer, N., Sullivan, M., Tucker, B., Abbott, T., Aguena, M., Allam, S., Avila, S., Bertin, E., Brooks, D., Buckley-Geer, E., Burke, D., Carnero Rosell, A., Carollo, D., Carrasco Kind, M., da Costa, L., De Vicente, J., Desai, S., Diehl, H., Doel, P., Eifler, T., Everett, S., Fosalba, P., Frieman, J., Garcia-Bellido, J., Gaztanaga, E., Gerdes, D., Gill, M., Glazebrook, K., Gruendl, R., Gschwend, J., Hartley, W., Hinton, S., Hollowood, D., Honscheid, K., James, D., Kuehn, K., Kuropatkin, N., Lima, M., Maia, M., March, M., Martini, P., Melchior, P., Menanteau, F., Miquel, R., Ogando, R., Paz-Chinchon, F., Plazas, A., Romer, A., Roodman, A., Sanchez, E., Scarpine, V., Serrano, S., Suchyta, E., Swanson, M., Tarle, G., Thomas, D., Tucker, D., Varga, T., Walker, A., Wilkinson, R., (DES Collaboration), 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.
  46. Cartwright, R., Beddingfield, C., Nordheim, T., Roser, J., Grundy, W., Hand, K., Emery, J., Cruikshank, D., Scipioni, F., 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.
  47. Dimitrova, T., Neugent, K., Levesque, E., 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.
  48. Wan, Z., Lewis, G., Li, T., Simpson, J., Martell, S., Zucker, D., Mould, J., Erkal, D., Pace, A., Mackey, D., Ji, A., Koposov, S., Kuehn, K., Shipp, N., Balbinot, E., Bland-Hawthorn, J., Casey, A., Da Costa, G., Kafle, P., Sharma, S., De Silva, G., 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.
  49. Margon, B., Massey, P., Neugent, K., Morrell, N., 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.
  50. Plavchan, P., Barclay, T., Gagne, J., Gao, P., Cale, B., Matzko, W., Dragomir, D., Quinn, S., Feliz, D., Stassun, K., Crossfield, I., Berardo, D., Latham, D., Tieu, B., Anglada-Escude, G., Ricker, G., Vanderspek, R., Seager, S., Winn, J., Jenkins, J., Rinehart, S., Krishnamurthy, A., Dynes, S., Doty, J., Adams, F., Afanasev, D., Beichman, C., Bottom, M., Bowler, B., Brinkworth, C., Brown, C., Cancino, A., Ciardi, D., Clampin, M., Clark, J., Collins, K., Davison, C., Foreman-Mackey, D., Furlan, E., Gaidos, E., Geneser, C., Giddens, F., Gilbert, E., Hall, R., Hellier, C., Henry, T., Horner, J., Howard, A., Huang, C., Huber, J., Kane, S., Kenworthy, M., Kielkopf, J., Kipping, D., Klenke, C., Kruse, E., Latouf, N., Lowrance, P., Mennesson, B., Mengel, M., Mills, S., Morton, T., Narita, N., Newton, E., Nishimoto, A., Okumura, J., Palle, E., Pepper, J., Quintana, E., Roberge, A., Roccatagliata, V., Schlieder, J., Tanner, A., Teske, J., Tinney, C., Vanderburg, A., von Braun, K., Walp, B., Wang, J., Wang, S., Weigand, D., White, R., Wittenmyer, R., Wright, D., Youngblood, A., Zhang, H., Zilberman, P., 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.
  51. Abbott, T., Aguena, M., Alarcon, A., Allam, S., Allen, S., Annis, J., Avila, S., Bacon, D., Bechtol, K., Bermeo, A., Bernstein, G., Bertin, E., Bhargava, S., Bocquet, S., Brooks, D., Brout, D., Buckley-Geer, E., Burke, D., Carnero Rosell, A., Carrasco Kind, M., Carretero, J., Castander, F., Cawthon, R., Chang, C., Chen, X., Choi, A., Costanzi, M., Crocce, M., da Costa, L., Davis, T., De Vicente, J., DeRose, J., Desai, S., Diehl, H., Dietrich, J., Dodelson, S., Doel, P., Drlica-Wagner, A., Eckert, K., Eifler, T., Elvin-Poole, J., Estrada, J., Everett, S., Evrard, A., Farahi, A., Ferrero, I., Flaugher, B., Fosalba, P., Frieman, J., Garcia-Bellido, J., Gatti, M., Gaztanaga, E., Gerdes, D., Giannantonio, T., Giles, P., Grandis, S., Gruen, D., Gruendl, R., Gschwend, J., Gutierrez, G., Hartley, W., Hinton, S., Hollowood, D., Honscheid, K., Hoyle, B., Huterer, D., James, D., Jarvis, M., Jeltema, T., Johnson, M., Johnson, M., Kent, S., Krause, E., Kron, R., Kuehn, K., Kuropatkin, N., Lahav, O., Li, T., Lidman, C., Lima, M., Lin, H., MacCrann, N., Maia, M., Mantz, A., Marshall, J., Martini, P., Mayers, J., Melchior, P., Mena-Fernandez, J., Menanteau, F., Miquel, R., Mohr, J., Nichol, R., Nord, B., Ogando, R., Palmese, A., Paz-Chinchon, F., Plazas, A., Prat, J., Rau, M., Romer, A., Roodman, A., Rooney, P., Rozo, E., Rykoff, E., Sako, M., Samuroff, S., Sanchez, C., Sanchez, E., Saro, A., Scarpine, V., Schubnell, M., Scolnic, D., Serrano, S., Sevilla-Noarbe, I., Sheldon, E., Smith, J., Smith, M., Suchyta, E., Swanson, M., Tarle, G., Thomas, D., To, C., Troxel, M., Tucker, D., Varga, T., von der Linden, A., Walker, A., Wechsler, R., Weller, J., Wilkinson, R., Wu, H., Yanny, B., Zhang, Y., Zhang, Z., Zuntz, J., DES Collaboration, 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.
  52. Hansen, T., Marshall, J., Simon, J., Li, T., Bernstein, R., Pace, A., Ferguson, P., Nagasawa, D., Kuehn, K., Carollo, D., Geha, M., James, D., Walker, A., Diehl, H., Aguena, M., Allam, S., Avila, S., Bertin, E., Brooks, D., Buckley-Geer, E., Burke, D., Rosell, A., Kind, M., Carretero, J., Costanzi, M., Da Costa, L., Desai, S., De Vicente, J., Doel, P., Eckert, K., Eifler, T., Everett, S., Ferrero, I., Frieman, J., Garcia-Bellido, J., Gaztanaga, E., Gerdes, D., Gruen, D., Gruendl, R., Gschwend, J., Gutierrez, G., Hinton, S., Hollowood, D., Honscheid, K., Kuropatkin, N., Maia, M., March, M., Miquel, R., Palmese, A., Paz-Chinchon, F., Plazas, A., Sanchez, E., Santiago, B., Scarpine, V., Serrano, S., Smith, M., Soares-Santos, M., Suchyta, E., Swanson, M., Tarle, G., Varga, T., Wilkinson, R., DES Collaboration, 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.
  53. Tokovinin, A., Mason, B., Mendez, R., Costa, E., 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).
  54. Schaefer, G., Beck, T., Prato, L., Simon, M., 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.
  55. Gutierrez, C., Sullivan, M., Martinez, L., Bersten, M., Inserra, C., Smith, M., Anderson, J., Pan, Y., Pastorello, A., Galbany, L., Nugent, P., Angus, C., Barbarino, C., Carollo, D., Chen, T., Davis, T., Della Valle, M., Foley, R., Fraser, M., Frohmaier, C., Gonzalez-Gaitan, S., Gromadzki, M., Kankare, E., Kokotanekova, R., Kollmeier, J., Lewis, G., Magee, M., Maguire, K., Moller, A., Morrell, N., Nicholl, M., Pursiainen, M., Sollerman, J., Sommer, N., Swann, E., Tucker, B., Wiseman, P., Aguena, M., Allam, S., Avila, S., Bertin, E., Brooks, D., Buckley-Geer, E., Burke, D., Carnero Rosell, A., Carrasco Kind, M., Carretero, J., Costanzi, M., da Costa, L., De Vicente, J., Desai, S., Diehl, H., Doel, P., Eifler, T., Flaugher, B., Fosalba, P., Frieman, J., Garcia-Bellido, J., Gerdes, D., Gruen, D., Gruendl, R., Gschwend, J., Gutierrez, G., Hinton, S., Hollowood, D., Honscheid, K., James, D., Kuehn, K., Kuropatkin, N., Lahav, O., Lima, M., Maia, M., March, M., Menanteau, F., Miquel, R., Morganson, E., Palmese, A., Paz-Chinchon, F., Plazas, A., Sako, M., Sanchez, E., Scarpine, V., Schubnell, M., Serrano, S., Sevilla-Noarbe, I., Soares-Santos, M., Suchyta, E., Swanson, M., Tarle, G., Thomas, D., Varga, T., Walker, A., Wilkinson, R., DES Collaboration, 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.
  56. Lidman, C., Tucker, B., Davis, T., Uddin, S., Asorey, J., Bolejko, K., Brout, D., Calcino, J., Carollo, D., Carr, A., Childress, M., Hoormann, J., Foley, R., Galbany, L., Glazebrook, K., Hinton, S., Kessler, R., Kim, A., King, A., Kremin, A., Kuehn, K., Lagattuta, D., Lewis, G., Macaulay, E., Malik, U., March, M., Martini, P., Moller, A., Mudd, D., Nichol, R., Panther, F., Parkinson, D., Pursiainen, M., Sako, M., Swann, E., Scalzo, R., Scolnic, D., Sharp, R., Smith, M., Sommer, N., Sullivan, M., Webb, S., Wiseman, P., Yu, Z., Yuan, F., Zhang, B., Abbott, T., Aguena, M., Allam, S., Annis, J., Avila, S., Bertin, E., Bhargava, S., Brooks, D., Carnero Rosell, A., Carrasco Kind, M., Carretero, J., Castander, F., Costanzi, M., da Costa, L., De Vicente, J., Doel, P., Eifler, T., Everett, S., Fosalba, P., Frieman, J., Garcia-Bellido, J., Gaztanaga, E., Gruen, D., Gruendl, R., Gschwend, J., Gutierrez, G., Hartley, W., Hollowood, D., Honscheid, K., James, D., Kuropatkin, N., Li, T., Lima, M., Lin, H., Maia, M., Marshall, J., Melchior, P., Menanteau, F., Miquel, R., Palmese, A., Paz-Chinchon, F., Plazas, A., Roodman, A., Rykoff, E., Sanchez, E., Santiago, B., Scarpine, V., Schubnell, M., Serrano, S., Sevilla-Noarbe, I., Suchyta, E., Swanson, M., Tarle, G., Tucker, D., Varga, T., Walker, A., Wester, W., Wilkinson, R., DES Collaboration, 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.
  57. Zenteno, A., Hernandez-Lang, D., Klein, M., Vergara Cervantes, C., Hollowood, D., Bhargava, S., Palmese, A., Strazzullo, V., Romer, A., Mohr, J., Jeltema, T., Saro, A., Lidman, C., Gruen, D., Ojeda, V., Katzenberger, A., Aguena, M., Allam, S., Avila, S., Bayliss, M., Bertin, E., Brooks, D., Buckley-Geer, E., Burke, D., Capasso, R., Carnero Rosell, A., Carrasco Kind, M., Carretero, J., Castander, F., Costanzi, M., da Costa, L., De Vicente, J., Desai, S., Diehl, H., Doel, P., Eifler, T., Evrard, A., Flaugher, B., Floyd, B., Fosalba, P., Frieman, J., Garcia-Bellido, J., Gerdes, D., Gonzalez, J., Gruendl, R., Gschwend, J., Gutierrez, G., Hartley, W., Hinton, S., Honscheid, K., James, D., Kuehn, K., Lahav, O., Lima, M., McDonald, M., Maia, M., March, M., Melchior, P., Menanteau, F., Miquel, R., Ogando, R., Paz-Chinchon, F., Plazas, A., Roodman, A., Rykoff, E., Sanchez, E., Scarpine, V., Schubnell, M., Serrano, S., Sevilla-Noarbe, I., Smith, M., Soares-Santos, M., Suchyta, E., Swanson, M., Tarle, G., Thomas, D., Varga, T., Walker, A., Wilkinson, R., DES Collaboration, 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.
  58. Pursiainen, M., Gutierrez, C., Wiseman, P., Childress, M., Smith, M., Frohmaier, C., Angus, C., Castro Segura, N., Kelsey, L., Sullivan, M., Galbany, L., Nugent, P., Bassett, B., Brout, D., Carollo, D., D'Andrea, C., Davis, T., Foley, R., Grayling, M., Hinton, S., Inserra, C., Kessler, R., Lewis, G., Lidman, C., Macaulay, E., March, M., Moller, A., Muller, T., Scolnic, D., Sommer, N., Swann, E., Thomas, B., Tucker, B., Vincenzi, M., Abbott, T., Allam, S., Annis, J., Avila, S., Bertin, E., Brooks, D., Buckley-Geer, E., Burke, D., Carnero Rosell, A., Carrasco Kind, M., da Costa, L., De Vicente, J., Desai, S., Diehl, H., Doel, P., Eifler, T., Everett, S., Flaugher, B., Frieman, J., Garcia-Bellido, J., Gaztanaga, E., Gerdes, D., Gruen, D., Gruendl, R., Gschwend, J., Gutierrez, G., Hollowood, D., Honscheid, K., James, D., Kim, A., Krause, E., Kuehn, K., Maia, M., Marshall, J., Menanteau, F., Miquel, R., Ogando, R., Palmese, A., Paz-Chinchon, F., Plazas, A., Roodman, A., Sanchez, E., Scarpine, V., Schubnell, M., Serrano, S., Sevilla-Noarbe, I., Suchyta, E., Swanson, M., Tarle, G., Wester, W., 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.
  59. Plavchan, P., Barclay, T., Gagne, J., Gao, P., Cale, B., Matzko, W., Dragomir, D., Quinn, S., Feliz, D., Stassun, K., Crossfield, I., Berardo, D., Latham, D., Tieu, B., Anglada-Escude, G., Ricker, G., Vanderspek, R., Seager, S., Winn, J., Jenkins, J., Rinehart, S., Krishnamurthy, A., Dynes, S., Doty, J., Adams, F., Afanasev, D., Beichman, C., Bottom, M., Bowler, B., Brinkworth, C., Brown, C., Cancino, A., Ciardi, D., Clampin, M., Clark, J., Collins, K., Davison, C., Foreman-Mackey, D., Furlan, E., Gaidos, E., Geneser, C., Giddens, F., Gilbert, E., Hall, R., Hellier, C., Henry, T., Horner, J., Howard, A., Huang, C., Huber, J., Kane, S., Kenworthy, M., Kielkopf, J., Kipping, D., Klenke, C., Kruse, E., Latouf, N., Lowrance, P., Mennesson, B., Mengel, M., Mills, S., Morton, T., Narita, N., Newton, E., Nishimoto, A., Okumura, J., Palle, E., Pepper, J., Quintana, E., Roberge, A., Roccatagliata, V., Schlieder, J., Tanner, A., Teske, J., Tinney, C., Vanderburg, A., von Braun, K., Walp, B., Wang, J., Wang, S., Weigand, D., White, R., Wittenmyer, R., Wright, D., Youngblood, A., Zhang, H., Zilberman, P., 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.
  60. 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.
  61. Flagg, L., Shkolnik, E., Weinberger, A., Bowler, B., Skiff, B., Kraus, A., Liu, M., 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.
  62. Pokhrel, R., Gutermuth, R., Betti, S., Offner, S., Myers, P., Megeath, S., Sokol, A., Ali, B., Allen, L., Allen, T., Dunham, M., Fischer, W., Henning, T., Heyer, M., Hora, J., Pipher, J., Tobin, J., Wolk, S., 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.
  63. Farkas-Takacs, A., Kiss, C., Vilenius, E., Marton, G., Muller, T., Mommert, M., Stansberry, J., Lellouch, E., Lacerda, P., Pal, A., 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.
  64. Scolnic, D., Smith, M., Massiah, A., Wiseman, P., Brout, D., Kessler, R., Davis, T., Foley, R., Galbany, L., Hinton, S., Hounsell, R., Kelsey, L., Lidman, C., Macaulay, E., Morgan, R., Nichol, R., Moller, A., Popovic, B., Sako, M., Sullivan, M., Thomas, B., Tucker, B., Abbott, T., Aguena, M., Allam, S., Annis, J., Avila, S., Bechtol, K., Bertin, E., Brooks, D., Burke, D., Rosell, A., Carollo, D., Kind, M., Carretero, J., Costanzi, M., da Costa, L., De Vicente, J., Desai, S., Diehl, H., Doel, P., Drlica-Wagner, A., Eckert, K., Eifler, T., Everett, S., Flaugher, B., Fosalba, P., Frieman, J., Garcia-Bellido, J., Gaztanaga, E., Gerdes, D., Glazebrook, K., Gruen, D., Gruendl, R., Gschwend, J., Gutierrez, G., Hartley, W., Hollowood, D., Honscheid, K., James, D., Kuehn, K., Kuropatkin, N., Lewis, G., Li, T., Lima, M., Maia, M., Marshall, J., Menanteau, F., Miquel, R., Palmese, A., Paz-Chinchon, F., Plazas, A., Pursiainen, M., Sanchez, E., Scarpine, V., Schubnell, M., Serrano, S., Sevilla-Noarbe, I., Sommer, N., Suchyta, E., Swanson, M., Tarle, G., Varga, T., Walker, A., Wilkinson, R., DES Collaboration, 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.
  65. Ragone-Figueroa, C., Granato, G., Borgani, S., De Propris, R., Garcia Lambas, D., Murante, G., Rasia, E., 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.
  66. Devogele, M., MacLennan, E., Gustafsson, A., Moskovitz, N., Chatelain, J., Borisov, G., Abe, S., Arai, T., Fedorets, G., Ferrais, M., Granvik, M., Jehin, E., Siltala, L., Pontinen, M., Mommert, M., Polishook, D., Skiff, B., Tanga, P., Yoshida, F., 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.
  67. Mommert, M., Hora, J., Trilling, D., Biver, N., Wierzchos, K., Harrington Pinto, O., Agarwal, J., Kim, Y., McNeill, A., Womack, M., Knight, M., Polishook, D., Moskovitz, N., Kelley, M., Smith, H., 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.
  68. Mommert, M., Trilling, D., Hora, J., Lejoly, C., Gustafsson, A., Knight, M., Moskovitz, N., Smith, H., 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.
  69. Smith, M., Sullivan, M., Wiseman, P., Kessler, R., Scolnic, D., Brout, D., D'Andrea, C., Davis, T., Foley, R., Frohmaier, C., Galbany, L., Gupta, R., Gutierrez, C., Hinton, S., Kelsey, L., Lidman, C., Macaulay, E., Moller, A., Nichol, R., Nugent, P., Palmese, A., Pursiainen, M., Sako, M., Swann, E., Thomas, R., Tucker, B., Vincenzi, M., Carollo, D., Lewis, G., Sommer, N., Abbott, T., Aguena, M., Allam, S., Avila, S., Bertin, E., Bhargava, S., Brooks, D., Buckley-Geer, E., Burke, D., Carnero Rosell, A., Carrasco Kind, M., Costanzi, M., da Costa, L., De Vicente, J., Desai, S., Diehl, H., Doel, P., Eifler, T., Everett, S., Flaugher, B., Fosalba, P., Frieman, J., Garcia-Bellido, J., Gaztanaga, E., Glazebrook, K., Gruen, D., Gruendl, R., Gschwend, J., Gutierrez, G., Hartley, W., Hollowood, D., Honscheid, K., James, D., Krause, E., Kuehn, K., Kuropatkin, N., Lima, M., MacCrann, N., Maia, M., Marshall, J., Martini, P., Melchior, P., Menanteau, F., Miquel, R., Paz-Chinchon, F., Plazas, A., Romer, A., Roodman, A., Rykoff, E., Sanchez, E., Scarpine, V., Schubnell, M., Serrano, S., Sevilla-Noarbe, I., Suchyta, E., Swanson, M., Tarle, G., Thomas, D., Tucker, D., Varga, T., Walker, A., DES Collaboration, 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.
  70. Muir, J., Bernstein, G., Huterer, D., Elsner, F., Krause, E., Roodman, A., Allam, S., Annis, J., Avila, S., Bechtol, K., Bertin, E., Brooks, D., Buckley-Geer, E., Burke, D., Carnero Rosell, A., Carrasco Kind, M., Carretero, J., Cawthon, R., Costanzi, M., da Costa, L., De Vicente, J., Desai, S., Dietrich, J., Doel, P., Eifler, T., Everett, S., Fosalba, P., Frieman, J., Garcia-Bellido, J., Gerdes, D., Gruen, D., Gruendl, R., Gschwend, J., Hartley, W., Hollowood, D., James, D., Jarvis, M., Kuehn, K., Kuropatkin, N., Lahav, O., March, M., Marshall, J., Melchior, P., Menanteau, F., Miquel, R., Ogando, R., Palmese, A., Paz-Chinchon, F., Plazas, A., Romer, A., Sanchez, E., Scarpine, V., Schubnell, M., Serrano, S., Sevilla-Noarbe, I., Smith, M., Suchyta, E., Tarle, G., Thomas, D., Troxel, M., Walker, A., Weller, J., Wester, W., Zuntz, J., DES Collaboration, 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.
  71. Lemon, C., Auger, M., McMahon, R., Anguita, T., Apostolovski, Y., Chen, G., Fassnacht, C., Melo, A., Motta, V., Shajib, A., Treu, T., Agnello, A., Buckley-Geer, E., Schechter, P., Birrer, S., Collett, T., Courbin, F., Rusu, C., Abbott, T., Allam, S., Annis, J., Avila, S., Bertin, E., Brooks, D., Burke, D., Carnero Rosell, A., Carrasco Kind, M., Carretero, J., Costanzi, M., da Costa, L., De Vicente, J., Desai, S., Eifler, T., Flaugher, B., Frieman, J., Garcia-Bellido, J., Gaztanaga, E., Gerdes, D., Gruen, D., Gruendl, R., Gschwend, J., Gutierrez, G., Honscheid, K., James, D., Kim, A., Krause, E., Kuehn, K., Kuropatkin, N., Lahav, O., Lima, M., Lin, H., Maia, M., March, M., Marshall, J., Menanteau, F., Miquel, R., Palmese, A., Paz-Chinchon, F., Plazas, A., Roodman, A., Sanchez, E., Schubnell, M., Serrano, S., Smith, M., Soares-Santos, M., Suchyta, E., Tarle, G., Walker, A., 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.
  72. Smith, I., Hayne, P., Byrne, S., Becerra, P., Kahre, M., Calvin, W., Hvidberg, C., Milkovich, S., Buhler, P., Landis, M., Horgan, B., Kleinbohl, A., Perry, M., Obbard, R., Stern, J., Piqueux, S., Thomas, N., Zacny, K., Carter, L., Edgar, L., Emmett, J., Navarro, T., Hanley, J., Koutnik, M., Putzig, N., Henderson, B., Holt, J., Ehlmann, B., Parra, S., Lalich, D., Hansen, C., Hecht, M., Banfield, D., Herkenhoff, K., Paige, D., Skidmore, M., Staehle, R., Siegler, M., 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.

  73. Petersburg, R., Ong, J., Zhao, L., Blackman, R., Brewer, J., Buchhave, L., Cabot, S., Davis, A., Jurgenson, C., Leet, C., McCracken, T., Sawyer, D., Sharov, M., Tronsgaard, R., Szymkowiak, A., Fischer, 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.
  74. Horch, E., van Belle, G., Davidson, J., Willmarth, D., Fekel, F., Muterspaugh, M., Casetti-Dinescu, D., Hahne, F., Granucci, N., Clark, C., Winters, J., Rupert, J., Weiss, S., Colton, N., Nusdeo, D., Henry, T., 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.
  75. Blackman, R., Fischer, D., Jurgenson, C., Sawyer, D., McCracken, T., Szymkowiak, A., Petersburg, R., Ong, J., Brewer, J., Zhao, L., Leet, C., Buchhave, L., Tronsgaard, R., Llama, J., Sawyer, T., Davis, A., Cabot, S., Shao, M., Trahan, R., Nemati, B., Genoni, M., Pariani, G., Riva, M., Fournier, P., Pawluczyk, R., 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.
  76. Burke, C., Baldassare, V., Liu, X., Foley, R., Shen, Y., Palmese, A., Guo, H., Herner, K., Abbott, T., Aguena, M., Allam, S., Avila, S., Bertin, E., Brooks, D., Carnero Rosell, A., Carrasco Kind, M., Carretero, J., da Costa, L., De Vicente, J., Desai, S., Doel, P., Eifler, T., Everett, S., Frieman, J., Garcia-Bellido, J., Gaztanaga, E., Gruen, D., Gruendl, R., Gschwend, J., Gutierrez, G., Hollowood, D., Honscheid, K., James, D., Krause, E., Kuehn, K., Maia, M., Menanteau, F., Miquel, R., Paz-Chinchon, F., Plazas, A., Sanchez, E., Santiago, B., Scarpine, V., Serrano, S., Sevilla-Noarbe, I., Smith, M., Soares-Santos, M., Suchyta, E., Swanson, M., Tarle, G., Tucker, D., Varga, T., Walker, A., DES Collaboration, 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.
  77. van Belle, G., Schaefer, G., von Braun, K., Nelan, E., Hartman, Z., Boyajian, T., Lopez-Morales, M., Ciardi, D., 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.
  78. Drlica-Wagner, A., Bechtol, K., Mau, S., McNanna, M., Nadler, E., Pace, A., Li, T., Pieres, A., Rozo, E., Simon, J., Walker, A., Wechsler, R., Abbott, T., Allam, S., Annis, J., Bertin, E., Brooks, D., Burke, D., Rosell, A., Carrasco Kind, M., Carretero, J., Costanzi, M., da Costa, L., De Vicente, J., Desai, S., Diehl, H., Doel, P., Eifler, T., Everett, S., Flaugher, B., Frieman, J., Garcia-Bellido, J., Gaztanaga, E., Gruen, D., Gruendl, R., Gschwend, J., Gutierrez, G., Honscheid, K., James, D., Krause, E., Kuehn, K., Kuropatkin, N., Lahav, O., Maia, M., Marshall, J., Melchior, P., Menanteau, F., Miquel, R., Palmese, A., Plazas, A., Sanchez, E., Scarpine, V., Schubnell, M., Serrano, S., Sevilla-Noarbe, I., Smith, M., Suchyta, E., Tarle, G., DES Collaboration, 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.
  79. Nadler, E., Wechsler, R., Bechtol, K., Mao, Y., Green, G., Drlica-Wagner, A., McNanna, M., Mau, S., Pace, A., Simon, J., Kravtsov, A., Dodelson, S., Li, T., Riley, A., Wang, M., Abbott, T., Aguena, M., Allam, S., Annis, J., Avila, S., Bernstein, G., Bertin, E., Brooks, D., Burke, D., Rosell, A., Kind, M., Carretero, J., Costanzi, M., da Costa, L., De Vicente, J., Desai, S., Evrard, A., Flaugher, B., Fosalba, P., Frieman, J., Garcia-Bellido, J., Gaztanaga, E., Gerdes, D., Gruen, D., Gschwend, J., Gutierrez, G., Hartley, W., Hinton, S., Honscheid, K., Krause, E., Kuehn, K., Kuropatkin, N., Lahav, O., Maia, M., Marshall, J., Menanteau, F., Miquel, R., Palmese, A., Paz-Chinchon, F., Plazas, A., Romer, A., Sanchez, E., Santiago, B., Scarpine, V., Serrano, S., Smith, M., Soares-Santos, M., Suchyta, E., Tarle, G., Thomas, D., Varga, T., Walker, A., DES Collaboration, 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.
  80. Nesvorny, D., Vokrouhlicky, D., Bottke, W., Levison, H., 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.
  81. Coffaro, M., Stelzer, B., Orlando, S., Hall, J., Metcalfe, T., Wolter, U., Mittag, M., Sanz-Forcada, J., Schneider, P., Ducci, L., 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.
  82. Buie, M., Porter, S., Tamblyn, P., Terrell, D., Parker, A., Baratoux, D., Kaire, M., Leiva, R., Verbiscer, A., Zangari, A., Colas, F., Diop, B., Samaniego, J., Wasserman, L., Benecchi, S., Caspi, A., Gwyn, S., Kavelaars, J., Ocampo Uria, A., Rabassa, J., Skrutskie, M., Soto, A., Tanga, P., Young, E., Stern, S., Andersen, B., Arango Perez, M., Arredondo, A., Artola, R., Ba, A., Ballet, R., Blank, T., Bop, C., Bosh, A., Camino Lopez, M., Carter, C., Castro-Chacon, J., Caycedo Desprez, A., Caycedo Guerra, N., Conard, S., Dauvergne, J., Dean, B., Dean, M., Desmars, J., Dieng, A., Bousso Dieng, M., Diouf, O., Dorego, G., Dunham, D., Dunham, J., Durantini Luca, H., Edwards, P., Erasmus, N., Faye, G., Faye, M., Ferrario, L., Ferrell, C., Finley, T., Fraser, W., Friedli, A., Galvez Serna, J., Garcia-Migani, E., Genade, A., Getrost, K., Gil-Hutton, R., Gimeno, G., Golub, E., Gonzalez Murillo, G., Grusin, M., Gurovich, S., Hanna, W., Henn, S., Hinton, P., Hughes, P., Josephs, J., Joya, R., Kammer, J., Keeney, B., Keller, J., Kramer, E., Levine, S., Lisse, C., Lovell, A., Mackie, J., Makarchuk, S., Manzano, L., Mbaye, S., Mbaye, M., Melia, R., Moreno, F., Moss, S., Ndaiye, D., Ndiaye, M., Nelson, M., Olkin, C., Olsen, A., Ospina Moreno, V., Pasachoff, J., Pereyra, M., Person, M., Pinzon, G., Pulver, E., Quintero, E., Regester, J., Resnick, A., Reyes-Ruiz, M., Rolfsmeier, A., Ruhland, T., Salmon, J., Santos-Sanz, P., Santucho, M., Sepulveda Nino, D., Sickafoose, A., Silva, J., Singer, K., Skipper, J., Slivan, S., Smith, R., Spagnotto, J., Stephens, A., Strabala, S., Tamayo, F., Throop, H., Torres Canas, A., Toure, L., Traore, A., Tsang, C., Turner, J., Vanegas, S., Venable, R., Wilson, J., Zuluaga, C., Zuluaga, J., 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.
  83. 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.
  84. Marsset, M., DeMeo, F., Binzel, R., Bus, S., Burbine, T., Burt, B., Moskovitz, N., Polishook, D., Rivkin, A., Slivan, S., Thomas, C., 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.
  85. 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.

  86. Moskovitz, N., Benson, C., Scheeres, D., Endicott, T., Polishook, D., Binzel, R., DeMeo, F., Ryan, W., Ryan, E., Willman, M., Hergenrother, C., Verveer, A., Lister, T., Birtwhistle, P., Sickafoose, A., Nagayama, T., Gilmore, A., Kilmartin, P., Benecchi, S., Sheppard, S., Marchis, F., Augusteijn, T., Smirnova, O., 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.
  87. Simon, J., Li, T., Erkal, D., Pace, A., Drlica-Wagner, A., James, D., Marshall, J., Bechtol, K., Hansen, T., Kuehn, K., Lidman, C., Allam, S., Annis, J., Avila, S., Bertin, E., Brooks, D., Burke, D., Rosell, A., Carrasco Kind, M., Carretero, J., da Costa, L., De Vicente, J., Desai, S., Doel, P., Eifler, T., Everett, S., Fosalba, P., Frieman, J., Garcia-Bellido, J., Gaztanaga, E., Gerdes, D., Gruen, D., Gruendl, R., Gschwend, J., Gutierrez, G., Hollowood, D., Honscheid, K., Krause, E., Kuropatkin, N., MacCrann, N., Maia, M., March, M., Miquel, R., Palmese, A., Paz-Chinchon, F., Plazas, A., Reil, K., Roodman, A., Sanchez, E., Santiago, B., Scarpine, V., Schubnell, M., Serrano, S., Smith, M., Suchyta, E., Tarle, G., Walker, A., DES Collaboration, 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.
  88. Chandler, C., Kueny, J., Trujillo, C., Trilling, D., Oldroyd, W., 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.
  89. 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%.
  90. Bourrier, V., Wheatley, P., Lecavelier des Etangs, A., King, G., Louden, T., Ehrenreich, D., Fares, R., Helling, C., Llama, J., Jardine, M., Vidotto, A., 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.
  91. Schmidt, C., Baumgardner, J., Moore, L., Bida, T., Swindle, R., Lierle, P., 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.
  92. Jenniskens, P., Moskovitz, N., Garvie, L., Yin, Q., Howell, J., Free, D., Albers, J., Samuels, D., Fries, M., Mane, P., Dunlap, D., Ziegler, K., Sanborn, M., Zhou, Q., Li, Q., Li, X., Liu, Y., Tang, G., Welten, K., Caffee, M., Busemann, H., Meier, M., Nesvorny, D., 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.
  93. 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%.
  94. 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.
  95. Cartwright, R., Emery, J., Grundy, W., Cruikshank, D., Beddingfield, C., Pinilla-Alonso, N., 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.
  96. Jenniskens, P., Lyytinen, E., Johannink, C., Odeh, M., Moskovitz, N., Abbott, T., 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.
  97. Grundy, W., Bird, M., Britt, D., Cook, J., Cruikshank, D., Howett, C., Krijt, S., Linscott, I., Olkin, C., Parker, A., Protopapa, S., Ruaud, M., Umurhan, O., Young, L., Dalle Ore, C., Kavelaars, J., Keane, J., Pendleton, Y., Porter, S., Scipioni, F., Spencer, J., Stern, S., Verbiscer, A., Weaver, H., Binzel, R., Buie, M., Buratti, B., Cheng, A., Earle, A., Elliott, H., Gabasova, L., Gladstone, G., Hill, M., Horanyi, M., Jennings, D., Lunsford, A., McComas, D., McKinnon, W., McNutt, R., Moore, J., Parker, J., Quirico, E., Reuter, D., Schenk, P., Schmitt, B., Showalter, M., Singer, K., Weigle, G., Zangari, A., 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.
  98. Spencer, J., Stern, S., Moore, J., Weaver, H., Singer, K., Olkin, C., Verbiscer, A., McKinnon, W., Parker, J., Beyer, R., Keane, J., Lauer, T., Porter, S., White, O., Buratti, B., El-Maarry, M., Lisse, C., Parker, A., Throop, H., Robbins, S., Umurhan, O., Binzel, R., Britt, D., Buie, M., Cheng, A., Cruikshank, D., Elliott, H., Gladstone, G., Grundy, W., Hill, M., Horanyi, M., Jennings, D., Kavelaars, J., Linscott, I., McComas, D., McNutt, R., Protopapa, S., Reuter, D., Schenk, P., Showalter, M., Young, L., Zangari, A., Abedin, A., Beddingfield, C., Benecchi, S., Bernardoni, E., Bierson, C., Borncamp, D., Bray, V., Chaikin, A., Dhingra, R., Fuentes, C., Fuse, T., Gay, P., Gwyn, S., Hamilton, D., Hofgartner, J., Holman, M., Howard, A., Howett, C., Karoji, H., Kaufmann, D., Kinczyk, M., May, B., Mountain, M., Patzold, M., Petit, J., Piquette, M., Reid, I., Reitsema, H., Runyon, K., Sheppard, S., Stansberry, J., Stryk, T., Tanga, P., Tholen, D., Trilling, D., 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.
  99. McKinnon, W., Richardson, D., Marohnic, J., Keane, J., Grundy, W., Hamilton, D., Nesvorny, D., Umurhan, O., Lauer, T., Singer, K., Stern, S., Weaver, H., Spencer, J., Buie, M., Moore, J., Kavelaars, J., Lisse, C., Mao, X., Parker, A., Porter, S., Showalter, M., Olkin, C., Cruikshank, D., Elliott, H., Gladstone, G., Parker, J., Verbiscer, A., Young, L., New Horizons Science Team, 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.
  100. Mau, S., Cerny, W., Pace, A., Choi, Y., Drlica-Wagner, A., Santana-Silva, L., Riley, A., Erkal, D., Stringfellow, G., Adamow, M., Carlin, J., Gruendl, R., Hernandez-Lang, D., Kuropatkin, N., Li, T., Martinez-Vazquez, C., Morganson, E., Mutlu-Pakdil, B., Neilsen, E., Nidever, D., Olsen, K., Sand, D., Tollerud, E., Tucker, D., Yanny, B., Zenteno, A., Allam, S., Barkhouse, W., Bechtol, K., Bell, E., Balaji, P., Crnojevic, D., Esteves, J., Ferguson, P., Gallart, C., Hughes, A., James, D., Jethwa, P., Johnson, L., Kuehn, K., Majewski, S., Mao, Y., Massana, P., McNanna, M., Monachesi, A., Nadler, E., Noel, N., Palmese, A., Paz-Chinchon, F., Pieres, A., Sanchez, J., Shipp, N., Simon, J., Soares-Santos, M., Tavangar, K., van der Marel, R., Vivas, A., Walker, A., Wechsler, R., 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.
  101. Protopapa, S., Olkin, C., Grundy, W., Li, J., Verbiscer, A., Cruikshank, D., Gautier, T., Quirico, E., Cook, J., Reuter, D., Howett, C., Stern, A., Beyer, R., Porter, S., Young, L., Weaver, H., Ennico, K., Dalle Ore, C., Scipioni, F., Singer, K., 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.
  102. Benson, C., Scheeres, D., Ryan, W., Ryan, E., 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.
  103. Liang, W., Johnson, J., Hayes, A., Lemmon, M., Bell, J., Grundy, W., Deen, R., 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.
  104. Beddingfield, C., Beyer, R., Singer, K., McKinnon, W., Runyon, K., Grundy, W., Stern, S., Bray, V., Dhingra, R., Moore, J., Ennico, K., Olkin, C., Schenk, P., Spencer, J., Weaver, H., Young, L., New Horizons Team, 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.
  105. Neugent, K., Massey, P., Georgy, C., Drout, M., Mommert, M., Levesque, E., Meynet, G., Ekstrom, S., 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.
  106. Sokal, K., Johns-Krull, C., Mace, G., Nofi, L., Prato, L., Lee, J., Jaffe, D., 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.
  107. Koposov, S., Boubert, D., Li, T., Erkal, D., Da Costa, G., Zucker, D., Ji, A., Kuehn, K., Lewis, G., Mackey, D., Simpson, J., Shipp, N., Wan, Z., Belokurov, V., Bland-Hawthorn, J., Martell, S., Nordlander, T., Pace, A., De Silva, G., Wang, M., S5 Collaboration, 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.
  108. Sickafoose, A., Bosh, A., Emery, J., Person, M., Zuluaga, C., Womack, M., Ruprecht, J., Bianco, F., Zangari, A., 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.
  109. Jardine, M., Collier Cameron, A., Donati, J., Hussain, G., 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.
  110. Weistrop, D., Nelson, C., Angione, R., Bachilla, R., 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.
  111. Rabinowitz, D., Benecchi, S., Grundy, W., Verbiscer, A., 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.
  112. Lopez-Rodriguez, E., Dowell, C., Jones, T., Harper, D., Berthoud, M., Chuss, D., Dale, D., Guerra, J., Hamilton, R., Looney, L., Michail, J., Nikutta, R., Novak, G., Santos, F., Sheth, K., Siah, J., Staguhn, J., Stephens, I., Tassis, K., Trinh, C., Ward-Thompson, D., Werner, M., Wollack, E., Zweibel, E., HAWC+Science Team, 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.
  113. Pendleton, Y., Cruikshank, D., Stern, S., Dalle Ore, C., Grundy, W., Materese, C., Protopapa, S., Schmitt, B., Lisse, C., 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.
  114. Kavanagh, R., Vidotto, A., O Fionnagain, D., Bourrier, V., Fares, R., Jardine, M., Helling, C., Moutou, C., Llama, J., Wheatley, P., 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.
  115. 114 publications and 3117 citations in 2020.

114 publications and 3117 citations total.

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