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Research involving Lowell Observatory staff 2018
(All publications)

This is a work ever in progress.

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Years: 2018 Bottom


  1. Ginsburg, A., Sipocz, B., Parikh, M., et al., (including Mommert, M.), 2018, zndo, astropy/astroquery: v0.3.9 release
    Functions and classes to access online data resources. Maintainers: @keflavich and @bsipocz. There is a paper about astroquery: http://arxiv.org/abs/1901.04520
  2. Trilling, D., Mommert, M., Hora, J., et al., 2018, AJ, 156, 261, Spitzer Observations of Interstellar Object 1I/Oumuamua
    1I/Oumuamua is the first confirmed interstellar body in our solar system. Here we report on observations of Oumuamua made with the Spitzer Space Telescope on 2017 November 21-22 (UT). We integrated for 30.2 hr at 4.5 m (IRAC channel 2). We did not detect the object and place an upper limit on the flux of 0.3 Jy (3). This implies an effective spherical diameter less than [98, 140, 440] m and albedo greater than [0.2, 0.1, 0.01] under the assumption of low, middle, or high thermal beaming parameter , respectively. With an aspect ratio for Oumuamua of 6:1, these results correspond to dimensions of [240:40, 341:57, 1080:180] m, respectively. We place upper limits on the amount of dust, CO, and CO2 coming from this object that are lower than previous results; we are unable to constrain the production of other gas species. Both our size and outgassing limits are important because Oumuamuas trajectory shows non-gravitational accelerations that are sensitive to size and mass and presumably caused by gas emission. We suggest that Oumuamua may have experienced low-level post-perihelion volatile emission that produced a fresh, bright, icy mantle. This model is consistent with the expected value and implied high-albedo value for this solution, but, given our strict limits on CO and CO2, requires another gas speciesprobably H2Oto explain the observed non-gravitational acceleration. Our results extend the mystery of Oumuamuas origin and evolution.
  3. Cauley, P., Shkolnik, E., Llama, J., et al., 2018, AJ, 156, 262, Evidence of Magnetic Star-Planet Interactions in the HD 189733 System from Orbitally Phased Ca II K Variations
    Magnetic star-planet interactions (SPI) provide a detection method and insight into exoplanet magnetic fields and, in turn, exoplanet interiors and atmospheric environments. These signatures can be sporadic and difficult to confirm for single-epoch observations of a system due to inhomogeneous stellar magnetospheres and periodic variability in stellar magnetism. Thus, an ideal SPI search consists of multiple epochs containing observations on consecutive nights spanning at least one complete planetary orbit. Such data sets are rare but do exist for some of the most intensely studied hot Jupiter systems. One such system is HD 189733 for which six suitable SPI data sets exist, the result of spectroscopic monitoring to perform some of the first SPI searches and also to study the stars magnetic field. Here we perform a uniform analysis of six archival Ca II K data sets for HD 189733, spanning 2006 June through 2015 July, in order to search for magnetic SPI signatures in the chromospheric line variations. We find significant evidence for modulations of Ca II K with a 2.29 0.04 day period in the 2013 August data, which is consistent with the planets orbital period. The peak in the orbital variations occurs at orb 0.9, which corresponds to the SPI emission leading the planet with a phase difference of 40 from the sub-planetary point. This is consistent with the phase-lead predictions of nonlinear force-free magnetic field SPI models. The stellar magnetic field strength at the planets orbit was greatest in 2013 August, which, due to the energy released in magnetic SPI scaling with B *, lends strength to the SPI interpretation.
  4. Massey, P., Levine, S., Neugent, K., et al., (including Skiff, B.), 2018, AJ, 156, 265, A Runaway Giant in the Galactic Halo
    New evidence provided by the Gaia satellite places the location of the runaway star J01020100-7122208 in the halo of the Milky Way (MW) rather than in the Small Magellanic Cloud (SMC) as previously thought. We conduct a reanalysis of the stars physical and kinematic properties, which indicates that the star may be an even more extraordinary find than previously reported. The star is a 180 Myr old 3-4 M G5-8 bright giant, with an effective temperature of 4800 100 K, a metallicity of Fe/H = -0.5, and a luminosity of {log}L/{L} =2.70+/- 0.20. A comparison with evolutionary tracks identifies the star as being in a giant or early asymptotic giant branch stage. The proper motion, combined with the previously known radial velocity, yields a total Galactocentric space velocity of 296 km s-1. The star is currently located 6.4 kpc below the plane of the MW, but our analysis of its orbit shows it passed through the disk 25 Myr ago. The stars metallicity and age argue against it being native to the halo, and we suggest that the star was likely ejected from the disk. We discuss several ejection mechanisms, and conclude that the most likely scenario is ejection by the MWs central black hole based upon our analysis of the stars orbit. The identification of the large radial velocity of J01020100-7122208 came about as a happenstance of it being seen in projection with the SMC, and we suggest that many similar objects may be revealed in Gaia data.

    This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

  5. Aadland, E., Massey, P., Neugent, K., et al., 2018, AJ, 156, 294, Shedding Light on the Isolation of Luminous Blue Variables
    In the standard view of massive star evolution, luminous blue variables (LBVs) are transitional objects between the most massive O-type stars and Wolf-Rayet (WR) stars. With short lifetimes, these stars should all be found near one another. A recent study of LBVs in the Large Magellanic Cloud (LMC) found instead that LBVs are considerably more isolated than either O-type stars or WRs, with a distribution intermediate between that of the WRs and red supergiants (RSGs). A similar study, using a more restricted sample of LBVs, reached the opposite conclusion. Both studies relied upon the distance to the nearest spectroscopically identified O-type star to define the degree of isolation. However, our knowledge of the spectroscopic content of the LMC is quite spotty. Here we re-examine the issue using carefully defined photometric criteria to select the highest-mass unevolved stars (bright blue stars, or BBSs), using spatially complete photometric catalogs of the LMC, M31, and M33. Our study finds that the LBVs are no more isolated than BBSs or WRs. This result holds no matter which sample of LBVs we employ. A statistical test shows that we can rule out the LBVs having the same distribution as the RSGs, which are about 2 more isolated. We demonstrate the robustness of our results using the second-closest neighbor. Furthermore, the majority of LBVs in the LMC are found in or near OB associations as are the BBS and WRs; the RSGs are not. We conclude that the spatial distribution of LBVs therefore is consistent with the standard picture of massive star evolution.
  6. Shkolnik, E., Ardila, D., Barman, T., et al., (including Llama, J.), 2018, AGUFM, 2018, P24C-05, A Dedicated Ultraviolet CubeSat for Astrophysics, SPARCS (Star Planet Activity Research CubeSat)
    Knowing the ultraviolet (UV) environments of planets orbiting low-mass stars (0.1-0.6 Msun; a.k.a. M dwarfs) will be crucial to understanding the composition of planetary atmospheres and a key parameter in discriminating between biological and abiotic sources for observed biosignatures. The Star-Planet Activity Research CubeSat (SPARCS) will be a 6U CubeSat devoted to photometric monitoring of M dwarfs in the far-UV and near-UV, measuring the time-dependent spectral slope, intensity and evolution of M dwarf stellar UV radiation. For each target, SPARCS will observe continuously over at least one complete stellar rotation (5 - 45 days). SPARCS will also advance UV detector technology by flying high quantum efficiency, UV-optimized detectors developed at JPL. These 2D-doped detectors have a long history of deployment demonstrating greater than five times the quantum efficiency of the detectors used by GALEX. SPARCS will pave the way for their application in missions like LUVOIR or HabEx, including interim UV-capable missions.

    Funding for SPARCS is provided by NASA's Astrophysics Research and Analysis program, NNH16ZDA001N.

  7. Thomas, C., Rivkin, A., Pravec, P., et al., (including Moskovitz, N.), 2018, AGUFM, 2018, P51A-02, Observations of Didymos: Past Results and Future Plans
    The binary near-Earth asteroid (65803) Didymos is the target for the two components of the Asteroid Impact and Deflection Assessment (AIDA) mission. The NASA DART (Double Asteroid Redirection Test) mission is scheduled to impact the Didymos secondary during its apparition in 2022. ESA's proposed Hera mission will arrive years later to obtain in situ observations of the system following the DART impact. One key scientific goal of AIDA is to measure and characterize the deflection caused by the impact. A combination of spacecraft and ground and space based optical and radar observations in 2022 will provide the required data for AIDA to meet its top-level mission goals.

    Photometric observations of Didymos were taken in 2003, 2015, and 2017. These observations have been used to determine the orbital period and constrain the orbital pole of the system. We used these observations to determine the number and precision of observations needed prior to the DART impact in 2022. We will observe the Didymos system during the 2019 and 2020-2021 apparitions to further characterize the system by obtaining additional lightcurve observations and spectra. These planned observations will provide us with the opportunity to establish the state of the system before impact to a high level of precision. We will place additional constraints on the inclination of the satellite orbit, the long-term effects of Binary YORP (BYORP), and whether the satellite is in synchronous rotation with the primary. The Didymos apparitions in 2019 and 2020-2021 will be much fainter than that in 2022. We anticipate observations at a range of large ground-based and space-based facilities. We will discuss what is currently known about the Didymos system, our observing plans prior to the DART impact, and our observing plans during the impact apparition.

  8. Smith, N., Mommert, M., Edwards, C., et al., 2018, AGUFM, 2018, P51D-2910, Thermophysical Properties of the Regolith of Phobos
    We present a map of the thermal inertia of the regolith of Phobos, based on observations collected by Mars Global Surveyor using the Thermal Emission Spectrometer (TES) instrument. We compare these observations with an airless body thermophysical model adapted for Phobos. By comparing brightness temperature spectra derived from our TES observations with simulated spectra generated by our thermophysical model, we can constrain the thermal properties of Phobos' surface.

    One such property, thermal inertia, describes how well a surface resists changes in temperature over time. Thermal inertia is controlled by the physical characteristics of that surface, such as the particle size of Phobos' regolith. Using 10 m measurements, we derive an average thermal inertia of 42 14 J m-2 K-1 s -1/2 for the observed region, with local variations ranging from 20 - 60 J m-2 K-1 s -1/2. This is similar to the 50 J m-2 K-1 s -1/2 thermal inertia of lunar regolith, composed primarily of fine dust.

    The observations used in this work cover roughly one hemisphere of Phobos, centered on the trailing side of the moon as it orbits around Mars. Previous estimates relied on disk-integrated observations, while this work made use of the disk-resolved observations collected by TES. Our results show a fairly uniform thermal inertia across the observed region, and are generally consistent with prior estimates.

    Using our thermophysical model, our result can be applied to investigate the temperature extremes present on Phobos, which vary both diurnally and seasonally.

  9. Monnier, J., Kraus, S., Ireland, M., et al., (including van Belle, G.), 2018, ExA, 46, 517, The planet formation imager
    The Planet Formation Imager (PFI, www.planetformationimager.org) is a next-generation infrared interferometer array with the primary goal of imaging the active phases of planet formation in nearby star forming regions. PFI will be sensitive to warm dust emission using mid-infrared capabilities made possible by precise fringe tracking in the near-infrared. An L/M band combiner will be especially sensitive to thermal emission from young exoplanets (and their disks) with a high spectral resolution mode to probe the kinematics of CO and H2O gas. In this paper, we give an overview of the main science goals of PFI, define a baseline PFI architecture that can achieve those goals, point at remaining technical challenges, and suggest activities today that will help make the Planet Formation Imager facility a reality.
  10. Leggett, S., Bergeron, P., Subasavage, J., et al., (including Levine, S.), 2018, ApJS, 239, 26, Distant White Dwarfs in the US Naval Observatory Flagstaff Station Parallax Sample
    This paper presents new trigonometric parallaxes and proper motions for 214 stars. The measurements were made at the US Naval Observatory Flagstaff Station between 1989 and 2017, and the average uncertainty in the parallax values is 0.6 mas. We find good agreement with Gaia Data Release 2 measurements for the stars in common, although there may be a small systematic offset similar to what has been found by other investigators. The sample is matched to catalogs and the literature to create a photometric data set that spans the ultraviolet to the mid-infrared. New mid-infrared photometry is obtained for 19 stars from archived Spitzer mosaics. New optical spectroscopy is presented for seven systems and additional spectra were obtained from the literature. We identify a subsample of 179 white dwarfs (WDs) at distances of 25-200 pc. Their spectral energy distributions (SEDs) are analyzed using model atmospheres. The models reproduce the entire flux-calibrated SED very well and provide the atmospheric chemical composition, temperature, surface gravity, mass, and cooling age of each WD. Twenty-six WDs are newly classified, and 12 systems are presented as candidate unresolved binaries. We confirm one WD+red dwarf system and identify two WDs as candidate dust disk systems. Twelve old and high-velocity systems are identified as candidate thick disk or halo objects. The WDs in the sample generally have Galactic disk-like ages of <8 Gyr and masses close to the canonical 0.6 M .
  11. Jenniskens, P., Albers, J., Tillier, C., et al., (including Moskovitz, N., Bright, L.), 2018, M&PS, 53, 2445, Detection of meteoroid impacts by the Geostationary Lightning Mapper on the GOES-16 satellite
    Bolides are detected by the Geostationary Lightning Mapper onboard the GOES-16 weather satellite, which takes images of Earth at a rate of 500 Hz in a 1.1 nm wide pass band centered on 777.4 nm wavelength. Ten case studies are discussed. These initial results were obtained using the Level 0 data received during the nonoperational in-orbit postlaunch test period. GLM positions and timings are sufficiently accurate to assist in trajectory and orbit reconstruction. GLM samples the light curve nearly completely, unaffected by onboard and downlink processes tailored to lightning data. Sufficient data on the instantaneous background scene are provided to reconstruct the baseline drift in the brightest pixels. The agreement to within a factor of 2-3 between measured total radiated energy from GLM and that derived from other space-borne observations implies that during the bolide's peak brightness the GLM pass band is dominated by continuum emission, rather than O I line emission. The reported flux is corrected for angle-from-nadir shifts in the central wavelength of the pass band, which overestimates continuum flux by only up to 20% for most of the GLM field of view, but more so if the bolide is observed far from nadir. Assuming a 6000 K blackbody spectrum, GLM is able to detect bolides with peak visual magnitude (at a normalized 100 km distance) brighter than about -14 in nighttime, and slightly brighter in daytime.
  12. Ahrens, C., Grundy, W., Mandt, K., et al., 2018, SSRv, 214, 130, Recent Advancements and Motivations of Simulated Pluto Experiments
    This review of Pluto laboratory research presents some of the recent advancements and motivations in our understanding enabled by experimental simulations, the need for experiments to facilitate models, and predictions for future laboratory work. The spacecraft New Horizons at Pluto has given a large amount of scientific data already rising to preliminary results, spanning from the geology to the atmosphere. Different ice mixtures have now been detected, with the main components being nitrogen, methane, and carbon monoxide. Varying geology and atmospheric hazes, however, gives us several questions that need to be addressed to further our understanding. Our review summarizes the complexity of Pluto, the motivations and importance of laboratory simulations critical to understanding the low temperature and pressure environments of icy bodies such as Pluto, and the variability of instrumentation, challenges for research, and how simulations and modeling are complimentary.
  13. Thirouin, A., Moskovitz, N., Binzel, R., et al., (including Burt, B., Pugh, T.), 2018, ApJS, 239, 4, The Mission Accessible Near-Earth Objects Survey: Four Years of Photometry
    Over 4.5 years, the Mission Accessible Near-Earth Object Survey assembled 228 near-Earth object (NEO) light curves. We report rotational light curves for 82 NEOs, constraints on amplitudes and periods for 21 NEOs, light curves with no detected variability within the image signal-to-noise and length of our observing block for 30 NEOs, and 10 tumblers. We uncovered two ultra-rapid rotators with periods below 20 s,2016 MA with a potential rotational periodicity of 18.4 s, and 2017 QG18 rotating in 11.9 sand estimated the fraction of fast/ultra-rapid rotators undetected in our project plus the percentage of NEOs with a moderate/long periodicity undetectable during our typical observing blocks. We summarize the findings of a simple model of synthetic NEOs to infer the objects morphology distribution using the measured distribution of light curve amplitudes. This model suggests that a uniform distribution of axis ratio can reproduce the observed sample. This suggests that the quantity of spherical NEOs (e.g., Bennu) is almost equivalent to the quantity of highly elongated objects (e.g., Itokawa), a result that can be directly tested thanks to shape models from Doppler delay radar imaging analysis. Finally, we fully characterized two NEOs2013 YS2 and 2014 FA7as appropriate targets for a potential robotic/human mission due to their moderate spin periods and low v.
  14. Hsieh, H., Ishiguro, M., Kim, Y., et al., (including Moskovitz, N., Thirouin, A.), 2018, AJ, 156, 223, The 2016 Reactivations of the Main-belt Comets 238P/Read and 288P/(300163) 2006 VW139
    We report observations of the reactivations of the main-belt comets (MBCs) 238P/Read and 288P/(300163) 2006 VW139 that also track the evolution of each objects activity over several months in 2016 and 2017. We additionally identify and analyze archival SDSS data showing 288P to have been active in 2000, meaning that both 238P and 288P have now each been confirmed to be active near perihelion on three separate occasions. From data obtained of 288P from 2012-2015 when it appeared inactive, we find best-fit R-band H, G phase function parameters of H R = 16.80 0.12 mag and G R = 0.18 0.11, corresponding to effective component radii of r c = 0.80 0.04 km, assuming a binary system with equally sized components. Fitting linear functions to ejected dust masses inferred for 238P and 288P soon after their observed reactivations in 2016, we find an initial average net dust production rate of {\dot{M}}d=0.7+/- 0.3 kg s-1 and a best-fit start date of 2016 March 11 (when the object was at a true anomaly of = -63) for 238P, and an initial average net dust production rate of {\dot{M}}d=5.6+/- 0.7 kg s-1 and a best-fit start date of 2016 August 5 (when the object was at = -27) for 288P. Applying similar analyses to archival data, we find similar start points for previous active episodes for both objects, suggesting that minimal mantle growth or ice recession occurred between the active episodes in question. Some changes in dust production rates between active episodes are detected, however. More detailed dust modeling is suggested to further clarify the process of activity evolution in MBCs.

    Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) (programs 12BH43, 15AT05, and 16BT05), which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de lUnivers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii, and at the Gemini Observatory (programs GN-2011B-Q-17, GN-2012A-Q-68, GN-2012B-Q-106, GN-2016B-LP-11, and GS-2016B-LP-11), which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the National Science Foundation (NSF) on behalf of the Gemini partnership: the NSF (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnologia e Innovacion Productiva (Argentina), and Ministerio da Ciencia, Tecnologia e Inovacao (Brazil).

  15. Neugent, K., Levesque, E., Massey, P., 2018, AJ, 156, 225, Binary Red Supergiants: A New Method for Detecting B-type Companions
    With the exception of a few well-known and studied systems, the binary population of red supergiants (RSGs) remains relatively uncharacterized. Famous systems such as VV Cep, 31 Cyg, and Aur contain RSG + B star binaries, and here we explore whether B stars are the main type of companion we expect from an evolutionary point of view. Using the Geneva evolutionary models, we find that this is indeed the case. However, few such systems are known, and we use model spectra to determine how easy such binaries would be to detect observationally. We find that it should be quite difficult to hide a B-type companion given a reasonable signal-to-noise in the optical/blue portion of the spectrum. We next examine spectra of Magellanic Cloud RSGs and newly acquired spectra of Galactic RSGs looking for new systems and refining our conclusions about what types of stars could be hidden in the spectra. Finally, we develop a set of photometric criteria that can help select likely binaries in the future without the overhead of large periodic or spectroscopic surveys.
  16. Docobo, J., Campo, P., Gomez, J., et al., (including Horch, E.), 2018, AJ, 156, 185, The Three-dimensional Orbit, Orbital Parallax, and Individual Masses of the Double-lined Spectroscopic Binaries HD 183255, HD 114882, and HD 30712
    Recent speckle observations performed at the Discovery Channel Telescope, the Gemini North Telescope, and the Special Astrophysical Observatory 6 m Telescope have permitted us to calculate the visual orbit of SB2 HD 114882 for the first time and to improve the visual orbits of two other SB2 systems, HD 30712 and HD 183255, using algorithms published by the authors of this research. Recently, new high-quality spectroscopic orbits have been obtained for these binaries by other authors. We determine their 3D orbits, individual masses, and orbital parallaxes, and present them in this paper. The parallaxes are compared with those available from the Gaia mission, and a comparison between the values confirms the precision of the results obtained here.
  17. Cauley, P., Kuckein, C., Redfield, S., et al., (including Llama, J.), 2018, AJ, 156, 189, The Effects of Stellar Activity on Optical High-resolution Exoplanet Transmission Spectra
    Chromospherically sensitive atomic lines display different spectra in stellar active regions, spots, and the photosphere, raising the possibility that exoplanet transmission spectra are contaminated by the contrast between various portions of the stellar disk. To explore this effect, we performed transit simulations of G-type and K-type stars for the spectral lines Ca II K at 3933 A, Na I 5890 A, H I 6563 A (H), and He I 10830 A. We find that strong facular emission and large coverage fractions can contribute a non-negligible amount to transmission spectra, especially for H, Ca II K, and Na I D, while spots and filaments are comparatively unimportant. The amount of contamination depends strongly on the location of the active regions and the intrinsic emission strength. In particular, active regions must be concentrated along the transit chord in order to produce a consistent in-transit signal. Mean absorption signatures in Na I and H, for example, can reach 0.2% and 0.3%, respectively, for transits of active latitudes with line emission similar in strength to moderate solar flares. Transmission spectra of planets transiting active stars, such as HD 189733, are likely contaminated by the contrast effect, although the tight constraints on active region geometry and emission strength make it unlikely that consistent in-transit signatures are due entirely to the contrast effect. He I 10830 A is not strongly affected and absorption signatures are likely diluted, rather than enhanced, by stellar activity. He I 10830 A should thus be considered a priority for probing extended atmospheres, even in the case of active stars.
  18. Cook, J., Ore, C., Protopapa, S., et al., (including Grundy, W.), 2018, Icar, 315, 30, Composition of Pluto's small satellites: Analysis of New Horizons spectral images
    On July 14, 2015, NASA's New Horizons spacecraft encountered the Pluto-system. Using the near-infrared spectral imager, New Horizons obtained the first spectra of Nix, Hydra, and Kerberos and detected the 1.5 and 2.0 m bands of H2O-ice on all three satellites. On Nix and Hydra, New Horizons also detected bands at 1.65 and 2.21 m that indicate crystalline H2O-ice and an ammoniated species, respectively. A similar band linked to NH3-hydrate has been detected on Charon previously. However, we do not detect the 1.99 m band of NH3-hydrate. We consider NH4Cl (ammonium chloride), NH4NO3 (ammonium nitrate) and (NH4)2CO3 (ammonium carbonate) as potential candidates, but lack sufficient laboratory measurements of these and other ammoniated species to make a definitive conclusion. We use the observations of Nix and Hydra to estimate the surface temperature and crystalline H2O-ice fraction. We find surface temperatures < 20 K ( <70 K with 1- error) and 23 K ( < 150 K with 1- error) for Nix and Hydra, respectively. We find crystalline H2O-ice fractions of 78-22+12 % and > 30% for Nix an Hydra, respectively. New Horizons observed Nix and Hydra twice, about 2-3 hours apart, or 5 and 25% of their respective rotation periods. We find no evidence for rotational differences in the disk-averaged spectra between the two observations of Nix or Hydra. We perform a pixel-by-pixel analysis of Nix's disk-resolved spectra and find that the surface is consistent with a uniform crystalline H2O-ice fraction, and a 50% variation in the normalized band area of the 2.21 m band with a minimum associated with the red blotch seen in color images of Nix. Finally, we find evidence for bands on Nix and Hydra at 2.42 and possibly 2.45 m, which we cannot identify, and, if real, do not appear to be associated with the ammoniated species. We do not detect other ices, such as CO2, CH3OH and HCN.
  19. Schenk, P., Beyer, R., McKinnon, W., et al., (including Grundy, W.), 2018, Icar, 315, 124, Breaking up is hard to do: Global cartography and topography of Pluto's mid-sized icy Moon Charon from New Horizons
    The 2015 New Horizons flyby through the Pluto system produced the first high-resolution topographic maps of Pluto and Charon, the most distant objects so mapped. Global integrated mosaics of the illuminated surface of Pluto's large icy moon Charon have been produced using both framing camera and line scan camera data (including four-color images at up to 1.47 km pixel scales), showing the best resolution data at all areas of the surface. Digital elevation models (DEMs) with vertical precisions of up to 0.1 km were constructed for 40% of Charon using stereo imagery. Local radii estimates for the surface were also determined from the cartographic control network solution for the LORRI framing camera data, which validate the stereo solutions. Charon is moderately cratered, the largest of which is 250-km across and 6 km deep. Charon has a topographic range over the observed hemisphere from lowest to highest of 19 km, the largest topographic amplitude of any mid-sized icy body (including Ceres) other than Iapetus. Unlike Saturn's icy moons whose topographic signature is dominated by global relaxation of topography and subsequent impact cratering, large-scale tectonics and regional resurfacing dominate Charon's topography. Most of Charon's encounter hemisphere north of the equator (Oz Terra) is broken into large polygonal blocks by a network of wide troughs with typically 3-6 km relief; the deepest of these occur near the illuminated pole and are up to 13 km deep with respect to the global mean radius, the deepest known surfaces on Charon. The edge of this terrain is defined by large tilted blocks sloping 5 or so, the crests of which rise to 5 or 6 km above Charon mean, the highest known points on Charon. The southern resurfaced plains, Vulcan Planitia, consist of rolling plains, locally fractured and pitted, that are depressed 1 km below the mean elevation of the disrupted northern terrains of Oz Terra that comprise much of the northern hemisphere (but 2-2.5 km below the surfaces of the blocks themselves). These plains roll downward gently to the south with a topographic range of 5 km. The outer margins of Vulcan Planitia along the boundary with Oz Terra form a 2-3-km-deep trough, suggesting viscous flow along the outer margins. Isolated massifs 2-4 km high, also flanked by annular moats, lie within the planitia itself. The plains may be formed from volcanic resurfacing of cryogenic fluids, but the tilted blocks along the outer margins and the isolated and tilted massifs within Vulcan Planitia also suggest that much of Charon has been broken into large blocks, some of which have been rotated and some of which have foundered into Charon's upper "mantle", now exposed as Vulcan Planitia, a history that may be most similar to the disrupted terrains of Ariel.
  20. Earle, A., Grundy, W., Howett, C., et al., 2018, Icar, 314, 195, Methane distribution on Pluto as mapped by the New Horizons Ralph/MVIC instrument
    The data returned from NASA's New Horizons spacecraft have given us an unprecedented, detailed look at the Pluto system. New Horizons' Ralph/MVIC (Multispectral Visible Imaging Camera) is composed of 7 independent CCD arrays on a single substrate. Among these are a red channel (540-700 nm), near-infrared channel (780-975 nm), and narrow band methane channel (860-910 nm). By comparing the relative reflectance of these channels we are able to produce high-resolution methane "equivalent width" (based on the 890 nm absorption band) and spectral slope maps of Pluto's surface. From these maps we can then quantitatively study the relationships between methane distribution, redness, and other parameters like latitude and elevation. We find Pluto's surface to show a great diversity of terrains, particularly in the equatorial region between 30N and 30S latitude. Methane "equivalent width" also shows some dependence on elevation (while spectral slope shows very little).
  21. Grundy, W., Bertrand, T., Binzel, R., et al., 2018, Icar, 314, 232, Pluto's haze as a surface material
    Pluto's atmospheric haze settles out rapidly compared with geological timescales. It needs to be accounted for as a surface material, distinct from Pluto's icy bedrock and from the volatile ices that migrate via sublimation and condensation on seasonal timescales. This paper explores how a steady supply of atmospheric haze might affect three distinct provinces on Pluto. We pose the question of why they each look so different from one another if the same haze material is settling out onto all of them. Cthulhu is a more ancient region with comparatively little present-day geological activity, where the haze appears to simply accumulate over time. Sputnik Planitia is a very active region where glacial convection, as well as sublimation and condensation rapidly refresh the surface, hiding recently deposited haze from view. Lowell Regio is a region of intermediate age featuring very distinct coloration from the rest of Pluto. Using a simple model haze particle as a colorant, we are not able to match the colors in both Lowell Regio and Cthulhu. To account for their distinct colors, we propose that after arrival at Pluto's surface, haze particles may be less inert than might be supposed from the low surface temperatures. They must either interact with local materials and environments to produce distinct products in different regions, or else the supply of haze must be non-uniform in time and/or location, such that different products are delivered to different places.
  22. Schenk, P., Beyer, R., McKinnon, W., et al., (including Grundy, W.), 2018, Icar, 314, 400, Basins, fractures and volcanoes: Global cartography and topography of Pluto from New Horizons
    The 2015 New Horizons flyby has produced the first high-resolution maps of morphology and topography of Pluto and Charon, the most distant objects so mapped. Global integrated mosaics of Pluto were produced using both LORRI framing camera and MVIC line scan camera data, showing the best resolution data obtained for all areas of the illuminated surface, 78% of the body. A unique feature of the Pluto imaging data set is the observation of terrains illuminated only by light scattered from atmospheric haze, allowing us to map terrains in the southern hemisphere that would otherwise have been in darkness. MVIC 4-color data were combined with the panchromatic map to produce full color global maps. Digital elevation models (DEMs) over 42% of Pluto were produced using combinations of MVIC hemispheric scans and LORRI mosaics, from which slopes at scales of 1 km can be determined. Pluto can be divided into regions each with distinct topographic signatures, corresponding with major physiographic terrain types. Large areas of Pluto are comprised of low-relief moderately cratered plains units. Deeply pitted and glaciated plains east of Sputnik Planitia are elevated 0.7 km. The most dominant topographic feature on Pluto is the 1200-by-2000-km wide depression enclosing the bright Sputnik Planitia ice sheet, the surface of which is 2.5-to-3.5 km deep (relative to the rim) and 2 km deep relative to the mean radius. The partial ring of steep-sided massifs, several of which are more than 5 km high, along the western margins of Sputnik Planitia produce some of the locally highest and steepest relief on Pluto, with slopes of 40-50. The second major topographic feature is a complex, eroded, ridge-trough system 300-400 km wide and at least 3200 km long extending north-to-south along the 155 meridian. This enormous structure has several kilometers of relief. It may predate the large impact event forming the basin, though some post-Sputnik Planitia deformation is evident. The large depressed, partially walled plain, Hyecho Palus, lies due southwest of Sputnik Planitia. Near the center of Hyecho Palus lie the circular constructional edifices Wright and Piccard Montes. Wright Mons rises 4.5 km above these plains, with a central depression 4.5 km deep, whereas Piccard Mons, best observed in haze-light, rises 5.5 km above the plains but has a bowl-shaped central depression 5.5 km below the plains for a total relief of up to 11 km, the greatest observed on Pluto. Both of these features are interpreted as constructional (volcanic?) in nature. Additional prominent topographic features include a 2-3 km high and 600 km wide dome centered on the illuminated IAU pole and the amoeboidal plateaus of "bladed" terrains in the equatorial region, which rise 2-5 km above local terrains and are the highest standing geologic units on the encounter hemisphere. The mean elevations in the integrated DEM for the two radio occultation areas are consistent with the 5-6 km difference in elevation as determined independently by the radio experiment, and a limb profile near the egress point confirms the presence of elevated bladed terrains in that area. Local relief of 3-5 km at massifs, troughs and pits supports conclusions that the icy shell of Pluto is relatively rigid. Numerous examples of topographic control of ice or frost deposition occur across Pluto, including the distinct coloration of the polar dome, the elevated terrains of eastern Tombaugh Regio, and along the ridge-trough system, where ridge tops and fossae rims are covered in different ices than at lower elevations. The topographic hypsogram of Pluto's encounter hemisphere is strongly bimodal due to the large Sputnik Planitia depression. Otherwise the topographic signature of Pluto is controlled by deviations from the otherwise dominant low plains, including elevated bladed terrain plateaus and the depressed volcanic province including Wright and Piccard Montes.
  23. Vilenius, E., Stansberry, J., Muller, T., et al., (including Mommert, M., Thirouin, A., Lykawka, P.), 2018, A&A, 618, A136, "TNOs are Cool": A survey of the trans-Neptunian region. XIV. Size/albedo characterization of the Haumea family observed with Herschel and Spitzer
    Context. A group of trans-Neptunian objects (TNOs) are dynamically related to the dwarf planet 136108 Haumea. Ten of them show strong indications of water ice on their surfaces, are assumed to have resulted from a collision, and are accepted as the only known TNO collisional family. Nineteen other dynamically similar objects lack water ice absorptions and are hypothesized to be dynamical interlopers.
    Aims: We have made observations to determine sizes and geometric albedos of six of the accepted Haumea family members and one dynamical interloper. Ten other dynamical interlopers have been measured by previous works. We compare the individual and statistical properties of the family members and interlopers, examining the size and albedo distributions of both groups. We also examine implications for the total mass of the family and their ejection velocities.
    Methods: We use far-infrared space-based telescopes to observe the target TNOs near their thermal peak and combine these data with optical magnitudes to derive sizes and albedos using radiometric techniques. Using measured and inferred sizes together with ejection velocities, we determine the power-law slope of ejection velocity as a function of effective diameter.
    Results: The detected Haumea family members have a diversity of geometric albedos 0.3-0.8, which are higher than geometric albedos of dynamically similar objects without water ice. The median geometric albedo for accepted family members is pV = 0.48-0.18+0.28, compared to 0.08-0.05+0.07 for the dynamical interlopers. In the size range D = 175-300 km, the slope of the cumulative size distribution is q = 3.2-0.4+0.7 for accepted family members, steeper than the q = 2.0 0.6 slope for the dynamical interlopers with D < 500 km. The total mass of Haumea's moons and family members is 2.4% of Haumea's mass. The ejection velocities required to emplace them on their current orbits show a dependence on diameter, with a power-law slope of 0.21-0.50.

    Herschel is an ESA space observatory with science instruments provided by a European-led Principal Investigator consortia and with important participation from NASA.

  24. Farnham, T., Knight, M., Bodewits, D., et al., (including Schleicher, D.), 2018, DPS, 50, 106.05, HST Observations of the Nucleus of Comet 41P/Tuttle-Giacobini-Kresak
    In early 2017, we discovered that comet 41P/Tuttle-Giacobini-Kresak (TGK), was spinning down at an incredibly rapid rate, with a rotation period that changed from 20 hours in early March (Farnham et al. CBET 4375, 2017) to 27 hours in late March (Knight et al. CBET 4377 2017) and >42 hours in early May (Bodewits et al. Nature 553, 186, 2017). These results indicate that the comet's rotation period decreased by 0.5 hr/day during this time periodthe fastest changes ever observed in any comet. Thus, TGK is ideal for testing models of cometary dynamics, allowing us to investigate how the torques respond to changing production rates and illumination conditions. Furthermore, if the spin-down of TGK continues at this pace over the next apparition or two, it may be possible to document a comet's behavior as it transitions through a slow-rotation end state (e.g., will it enter a stage of complex rotation? Spin up in the opposite direction? Or will it exhibit some other response?). To follow up on this work, we were awarded 10 orbits of HST WFC3/UVIS time in December 2017 to observe the lightcurve of TGK. Our goal is to characterize the rotation state of the nucleus after its activity had subsided. Results from this work will not only provide a measurement of the "final" spin state achieved during the 2017 apparition, but will also define the initial state for future monitoring of any continuing changes over the next apparition. We can also take advantage of the high resolution of the HST images to separate the nucleus signal from that of any coma that is present. This allows us to constrain properties of the nucleus, including its general size and shape, that will be used in models of the comet's dynamical evolution. Although we requested our 10 orbits to be spaced over a 7-day baseline to cover any expected rotation period, scheduling constraints forced us to restrict our observational window to 3.5 days. This affects our ability to fully define the lightcurve, but otherwise our analyses will continue as planned. We will present results from this work, and will discuss how they might relate to the rapid evolution of the comet's dynamics.
  25. Pinilla-Alonso, N., Popescu, M., Fernandez-Valenzuela, E., et al., (including Murillo, R.), 2018, DPS, 50, 200.02, The hypnotic dance of Patroclus and Menoetius: Ground-based observations of their 2017-2018 mutual event season.
    Trojans are a significant portion of the small bodies population located within two clouds in the L4 and L5 Lagrangian points of Jupiter's orbit. The study of primitive small bodies is relevant to the origin and nature of volatile and organic material in the early Solar System. Dedicated studies of the nature of these bodies can significantly improve our understanding of their nature, origin and evolutionary mechanisms. Lucy, a mission of the NASA's Discovery Program, is planned to launch in October 2021 for a 12-year journey. Lucy will explore seven different primitive small bodies, six of which will be Trojans. The mission will use a suite of remote sensing instruments to map the geology, surface color, composition, thermal and other physical properties of the targets at close range. Our international team performed observations during 2017 and 2018 to record the light-curve of the mutual events of the binary system formed by Patroclus and Menoetius, providing a unique opportunity to refine their orbit characteristics as well as other properties of the system (sizes, shape, and mass of both objects). Patroclus is the first binary trojan to be discovered. Previous studies by Marchis, et al. (2016, Nature, 439) determined the mutual orbit of the system to have a period of 4.283 0.004 days and a semimajor axis of 680 20 km, leading to a system mass of (1.36 0.11) x 1018kg and an average bulk density of 0.8 0.2 g cm-3. When the plane of their mutual orbit is aligned with the direction to the Sun or to an observer, Patroclus and Menoetius take turns eclipsing or occulting one another. Such an alignment occurs during mutual event seasons, twice during the 12 year orbit around the Sun. We show, for the first time, a collection of light-curves that are the result of about 20 detections. Our analysis puts a special focus on the differences between the observations and the models of the orbit (Grundy et al. 2018, Icarus 305) providing unique and crucial information that includes the possible topographic variation on Menoetius' south pole, a refinement to the orbit model, and improved predictions for shadowing and occultation events.
  26. Hanley, J., Groven, J., Grundy, W., et al., 2018, DPS, 50, 203.10, Characterization of Possible Two Liquid Layers in Titan Seas
    The lakes and seas of Titan are composed primarily of methane and ethane, with the concentration of dissolved nitrogen from the atmosphere dependant on the ratio of methane to ethane, the temperature, and pressure. Previous models have predicted the existence of two liquid layers in equilibrium with the vapor phase under certain temperature and pressure conditions (e.g. Cordier et al., 2017, Nature Astronomy). Our previous experiments have confirmed the presence of the two liquid phase at colder temperatures and higher pressures than what exists on the surface of Titan. In the Astrophysical Ices Lab at Northern Arizona University, we have performed a new series of experiments to understand the conditions under which the two liquid layers will form. We have incorporated Raman spectroscopy to allow us to measure the composition of the samples. In all experiments performed so far, the lower layer is enriched in nitrogen and methane, while the upper layer is enriched in methane and ethane, although both layers have all three species present. The initial ratio of methane to ethane will control the relative volumes of the two liquids, though it does not appear to affect their compositions. Comparing to Cordier et al. (2017), we find the two liquid phase does not form at 85 K until a pressure of greater than 1.83 bar is reached, compared to the 1.7 bar predicted. Our results show that at Titan surface pressure (1.44 bar), a mixture of methane, ethane and nitrogen will remain in one liquid down to 82 K, where it will then split into two liquids. We will present these experimental results detailing the conditions under which the two liquid phases form, as well as the composition of the liquids. These results can inform whether they might occur on Titan, and how that might impact understanding of previous mission results from Cassini, as well as future missions, and guide current theoretical models.
  27. Bair, A., Schleicher, D., Farnham, T., 2018, DPS, 50, 210.06, The Extremely Active Comet C/Hale-Bopp (1995 O1): Production Rates from Nearly Five Years of Narrowband Photometry
    Comet C/Hale-Bopp (1995 O1) was an intrinsically bright object that exhibited the highest continuous gas and dust production rates ever measured for a comet. We will report on our extensive narrowband photometry observations of H-B, including 332 individual sets of photometry obtained on a total of 98 nights at Lowell and Perth Observatories. Our observations span nearly 5 years, beginning with inbound measurements on 1995 July 25 (heliocentric distance, r, of 7.14 AU), continuing through perihelion (1997 April 1; perihelion distance of 0.91 AU), then extending outbound until 2000 March 3 (r of 10.58 AU). A thorough analysis of this dataset has been delayed for numerous reasons, including the long timeline of post-perihelion observations and the calibrating of our then-new HB comet filter set (Farnham et al. 2000, Icarus 147, 180). We additionally discovered that, due to its extremely high production rates, the size of the collision zone for H-B was much larger than normal, especially near perihelion, requiring an adjustment to our standard scalelengths and an empirical adjustment to the derived water production rates. From our first observations, it was clear that H-B was unique. The dust production, even at 7.14 AU, had an Af of 50,000 cm - much higher than that measured for any comet in our database at any heliocentric distance. H-B's highest production rates were measured near perihelion, where Af peaked at 1.2106 cm and the water production rate, also by far our highest value measured for any comet, reached 3.591031 molecules s-1. The effective active area required to produce the measured water production is 2100 km2, implying a minimum nucleus diameter of 26 km; however the existence of isolated jets strongly indicates that the entire surface of the nucleus is not active, which means the actual size is likely to be at least 2 as large. These and other results from this unique comet will be presented. This research has been supported by NASA's Planetary Astronomy Program.
  28. Schleicher, D., Knight, M., 2018, DPS, 50, 210.12, Narrowband Observations of Comet 21P/Giacobini-Zinner During Its Excellent 2018 Apparition
    During its last excellent apparition in 1985, Comet 21P/Giacobini-Zinner was discovered to have a highly unusual composition, with C2 and C3 each depleted by about a factor of six compared to either OH or CN (Schleicher et al. 1987), making G-Z the prototype of what would become the carbon-chain depleted compositional class (A'Hearn et al. 1995). The comet also exhibited an odd pre-/post-perihelion asymmetry, with all production rates dropping by a factor of several in the six weeks surrounding perihelion. The current apparition, with very similar circumstances to that of 1985, presents an exceptional opportunity to further study this interesting object. The goals of our multi-instrument observing campaign from Lowell Observatory include greatly extending the heliocentric distance range over which we measure production rates, obtaining narrowband images to study expected jet morphology, and obtaining high resolution spectroscopy to measure isotopic ratios when the comet is brightest in September (though spectroscopic results are not expected to be available in time for presentation). Thus far we have obtained a total of 21 sets of photometry over five nights beginning May 17 (1.82 AU), and imaging on 11 nights beginning June 13 (1.57 AU). Based on the strong asymmetry in production rates about perihelion that we measured in 1985, along with successful studies of seasonal effects in several other comets in recent years, we predicted that G-Z was likely to have a single dominant jet whose source was in summer inbound and rapidly changed to winter near perihelion. Indeed, our new imaging exhibits a broad feature towards the northeast having about 120 width that shows little rotational variation. This is consistent with a mid-to-high latitude source region perpetually in sunlight producing a filled corkscrew of material. How this feature evolves during this apparition, a preliminary model of G-Z's jet morphology, along with associated photometric results, will be presented. This research is supported by NASA Planetary Astronomy Program grant NNX14AG81G and Solar System Observations Program grant 80NSSC18K0856.
  29. Noll, K., Grundy, W., Buie, M., et al., 2018, DPS, 50, 217.04, Deep Search for Satellites of Lucy Trojans with HST
    We report on the first deep satellite search of the Trojan asteroids that are targets of NASA's Lucy mission. This search was carried out using the Hubble Space Telescope in a 10 orbit program in cycle 25. The observations were obtained from February - September 2018. The primary goal of the observations is to search for faint companions to the Trojans that will be visited by the Lucy spacecraft. Deep imaging was accomplished using WFC3 UVIS in standard imaging mode with the F555W filter which delivers good PSF quality and high sensitivity. The observations were designed to reach S/N=5 for a limiting magnitude of V25.5 at separations 0.2 arcsec from the primary object which approximates the Lucy spacecraft encounter distance. The search can detect satellites at least five magnitudes fainter than the faintest target, Polymele. At closer separations PSF fitting is required to search for close-in any satellites. The UVIS2-C1K1C subarray was used for all observations and covers the entire stable region of the Hill spheres of our targets. The Lucy mission was selected by NASA in January 2017 and is planned for launch in October 2021. Early discovery of any satellites will enable early planning for observations and significantly enhance the scientific return of the mission. Orbiting material is also a potential spacecraft hazard and a deep search for any evidence of bound material is a necessary precaution for the mission. At the time of the abstract deadline two of the five targets have been observed with HST - all are scheduled to be observed by the end of September. We will report on the latest results.
  30. Dalle Ore, C., Cruikshank, D., Protopapa, S., et al., (including Grundy, W.), 2018, DPS, 50, 221.07, Ammonia on Pluto: its detection and implications
    Pluto was observed at high spatial resolution during the New Horizons flyby on July 14th, 2015 by the near-infrared spectral imager (Linear Etalon Imaging Spectral Array, LEISA, 2700 m/pixel) and CCD camera (Multi-spectral Visible Imaging Camera, MVIC, 650 m/pixel) system. In the striking diversity of the surface, Virgil Fossae, part of Cthulhu Macula, stands out as uniquely red. This is a region of past extensional tectonics, whose pattern appears to radiate away from Sputnik Planitia and the basin in which it lies. A detailed analysis of this geographical area unveils a spectral signature characteristic of ammonia in water ice, its hydrate, ammoniated salts, or a combination of the above. Ammonia is an important molecule both as a tracer of chemical evolution in the Solar System and as a modifier of the physical properties of bedrock water ice. Lowering the freezing point of water ice, ammonia potentially allows for liquid water to be present in the interiors of icy bodies with a core heated by radioactive decay. On Pluto, we find that the presence of ammonia provides evidence of past and possibly geologically recent activity, supporting the hypothesis of a subterranean body of water and cryovolcanic activity. We present a detailed analysis of the near-IR spectrum of Pluto leading to the discovery of this important feature.
  31. Dustrud, S., Lindberg, G., Grundy, W., et al., (including Hanley, J.), 2018, DPS, 50, 221.09, Modeling the Phase Diagram and Properties of Titan's Lakes via Molecular Dynamics
    Nitrogen, methane, and ethane are abundant on Titan. The ternary system of these three compounds is present as liquids in lakes and seas. Knowledge of their phase behavior and thermodynamic properties is crucial for understanding the behaviors of Titan's fluid bodies and their interaction with the surface and atmosphere. The development of a full phase diagram is of fundamental importance in the understanding of how the bodies of liquid behave on the surface of Titan; additionally, the material properties such as, densities, heat capacities, or viscosity are vital to better the understanding of the stability of the liquids and their bulk behavior. Utilizing a thermodynamic approach that assumes ideality of the system, phase behavior can be predicted. Molecular dynamics simulations (MD) offer a unique insight to the harsh conditions of the outer solar system, enabling the real effects of non-ideal interactions to be quantified. Material properties can then be calculated from the results of MD simulations for a variety of compositions and conditions. MD offers not only common observables, but it also provides an understanding at the atomistic level of what occurs in a mixture. Combining a theoretical approach with experimental, the exact boundaries of the predicted phase transitions can be elucidated and the theoretical approach validated. The Astrophysics Ice Lab at Northern Arizona University is home to a laboratory apparatus capable of cooling samples to 30K, and designed with windows to allow for spectroscopy of a bulk sample. Raman spectroscopy in particular is a powerful tool in evaluating the interactions between molecules within a mixture and allows for a more in-depth study of the systems in question. We will present on our findings and material properties calculated from MD simulations of the ternary mixture under conditions relevant to Titan.
  32. Trilling, D., McNeill, A., Mommert, M., et al., 2018, DPS, 50, 301.04, Spitzer observations of `Oumuamua and `Oumuamua's density and shape
    1I/`Oumuamua is the first confirmed interstellar body in our Solar System. Here we report on 4.5 micron observations of `Oumuamua made with the Spitzer Space Telescope on 2017 November 21-22. We did not detect the object and place an upper limit on its flux. This implies an effective spherical diameter upper limit and albedo lower limit, with a range of values that depends on what value of the thermal beaming parameter is used. We also place upper limits on the amount of dust, CO, and CO2 that are emitted from this object that are lower than previous results; we are unable to constrain the production of other gas species. We also present our estimate of `Oumuamua's density and aspect ratio (elongation). There is no description of the suite of `Oumuamua's physical properties that corresponds to any population of bodies in our Solar System. Our results extend the mystery about `Oumuamua's origin and evolution.
  33. Fraser, W., Bannister, M., Marsset, M., et al., (including Thirouin, A.), 2018, DPS, 50, 302.04, Col-OSSOS: The Compositional Structure of the Protoplanetesimal Disk
    The surfaces of trans-Neptunian objects (TNOs) are poorly understood. Small TNOs fall into at least three classes of object based on their surface colours and albedo. Despite nearly two decades of gathering TNO surface information, a taxonomy has still not been agreed upon. The development of a robust taxonomy is one of the goals of the Colours of the Outer Solar System Origins Survey (Col-OSSOS). After a quick overview of the program, we present taxonomic results from Col-OSSOS. From u, g, r, z and J photometry of a sample of 79 TNOs, we find evidence for only three separate taxons based on their colours. One of the taxons consists entirely of a single dynamical population, the so-called cold classical TNOs, which stand out in colour space, possessing unique (r-z) compared to similarly optically red dynamically excited TNOs. The other two taxons are the known neutral and red classes of dynamically excited TNOs, which are approximately divided by optical colour at (g-r)=0.75. These classes exhibit a broad continuum in colour, rather than occupying similar mean colours for all class members. From albedo considerations, we demonstrate that in the dynamically excited populations, the neutral class outnumbers the red class by at least a factor of 4, but could be as numerous as 11:1. The minimal number of detected taxons argues for a moderately homogenous protoplanetary disk, with only a pair of substantive compositional divisions spanning roughly 20-45 AU, and a disk which is heavily dominated by the neutral class of object.
  34. Thirouin, A., Sheppard, S., 2018, DPS, 50, 302.05, Lightcurves of the Dynamically Cold Classical Trans-Neptunian Objects
    The dynamically Cold Classical trans-Neptunian objects (TNOs) have low inclination, low eccentricity, and are not in Neptune resonances. Because they have likely remained far from the Sun, and formed near where they exist today, these TNOs are thought to be primordial and thus important to understand our Solar System's formation and evolution. Even though more than 600 Cold Classicals (CCs) are known, only 19 have been studied for rotational lightcurves. In addition to this low number, most of the studied CCs are the larger objects and known wide binary systems and thus our understanding of this population is highly biased. Therefore, in order to improve our knowledge of the CCs and give context to the next flyby of the NASA's New Horizons mission, we started a survey of the CCs with the Discovery Channel and the Magellan telescopes for lightcurves and colors. Our survey is the first entirely dedicated to the study of the rotational and physical properties of this population. Over the past three years, we observed some 40 non-binary CCs with absolute magnitudes from 5 to 7.2 mag. Sparse and complete lightcurves obtained through our survey are used to constrain the contact binary fraction, the shape and rotational frequency distributions of the CCs. By comparing the properties of the Cold Classicals to the other dynamical groups, we aim to extract the primordial characteristics of the trans-Neptunian population. We also report the discovery of the first two likely contact binaries detected through lightcurves in this dynamical group. Using our results and the literature, we estimate that only about 10% of the CCs could be contact binaries, which is significantly lower than our estimate of contact binaries in the Plutino population of some 40-50%. This low population of CC contact binaries is also surprising given that the CC have a larger fraction of equal-sized wide-binary systems while the Plutinos have very few known wide binaries. This suggests the different scattering histories of the TNO populations affected the formation of contact binaries. Finally, a new equal-sized wide binary, 2014 LQ28, was identified from our observations. This work is supported by the National Science Foundation, grant #1734484.
  35. Grundy, W., Noll, K., Roe, H., et al., 2018, DPS, 50, 305.01, Tightly-bound transneptunian binaries have prograde mutual orbits
    We report on our continuing efforts to determine the orbits of transneptunian binaries (TNBs), using data from Hubble Space Telescope and adaptive optics systems on large ground-based telescopes. We have expanded the sample of TNBs with fully determined orbits to around 40% of the known TNBs, with another 20% having known periods, eccentricities, and semimajor axes, but ambiguous orientations. Excluding planet-sized objects where the satellites could be more likely to have formed through giant impacts, the smaller TNBs show a stark contrast in orbital orientations between tightly bound binaries (with semimajor axes less than around 5% of the Hill radius) and more loosely bound binaries. Among the tight binaries, prograde mutual orbits vastly outnumber retrograde orbits. This imbalance is not attributable to any known observational bias. We argue that it is a key clue to the formation environment of outer solar system planetesimals, favoring gravitational collapse from regions enriched in solids via mechanisms such as the streaming instability. Unlike the tight binaries, wider binaries are evenly distributed between prograde and retrograde orbits, but with mutual orbits favoring alignment or anti-alignment with their heliocentric orbits. This pattern is consistent with expectation from Kozai-Lidov cycles coupled with tidal evolution eliminating initially high inclination wide binaries.
  36. DeMeo, F., Polishook, D., Carry, B., et al., (including Burt, B., Moskovitz, N.), 2018, DPS, 50, 310.07, Olivine-dominated A-type asteroids in the Main Belt: Distribution, Abundance and Relation to Families
    Differentiated asteroids are rare in the main asteroid belt despite evidence for 100 distinct differentiated bodies in the meteorite record. We have sought to understand why so few main belt asteroids differentiated and where those differentiated bodies or fragments reside. Using the Sloan Digital Sky Survey (SDSS) to search for a needle in a haystack we identify spectral A-type asteroid candidates, olivine-dominated asteroids that may represent mantle material of differentiated bodies. We have performed a near-infrared spectral survey with SpeX on the NASA IRTF and FIRE on the Magellan Telescope. The success rate for confirming A-types from SDSS candidates is 33% - 20 of the 60 objects observed. We report results from having doubled the number of known A-type asteroids. We deduce a new estimate for the overall abundance and distribution of this class of olivine-dominated asteroids. We find A-type asteroids account for less than 0.16% of all main-belt objects larger than 2 km and estimate there are a total of 600 A-type asteroids above that size. They are found rather evenly distributed throughout the main belt, are even detected at the distance of the Cybele region, and have no statistically significant concentration in any asteroid family. We conclude the most likely implication is the few fragments of olivine-dominated material in the main belt did not form locally, but instead were implanted as collisional fragments of bodies that formed elsewhere.
  37. Bosh, A., Sickafoose, A., Levine, S., et al., (including Genade, A.), 2018, DPS, 50, 311.01, The 2017 occultation by Vanth: a revised analysis
    In March 2017, we observed an occultation by members of the Orcus system. Two chords were obtained, along with three negative detections (Sickafoose et al. 2017; Sickafoose et al. 2018, submitted). Initial geometric analysis of these data was consistent with an occultation by Orcus and Vanth, of a single star (Bosh et al. 2017). Subsequent speckle imaging of the occultation star using DSSI on Gemini-South (Horch et al. 2009) revealed a double star with a separation of 252 mas and a magnitude difference of 0.93 at 692 nm. Reanalysis of the geometry of this event with this new stellar information shows that the two positive detections are consistent with occultations by Orcus' satellite Vanth at both the 3-m IRTF (chord length 434.39 2.36 km) and the 1-m Las Cumbres ELP telescope at McDonald Observatory (chord length 291.1 124.9 km; larger uncertainty due to deadtime uncertainty). These observations suggest that the IRTF chord was close to being central on Vanth; in fact, it must be near central because a non-detection at Sierra Remote Observatories (0.6-m ATUS) constrains the geometry. We are not able to determine if there is any deviation from sphericity due to the uncertainty in the chord length of our second chord, from ELP, however it is consistent with a spherical shape for Vanth. Initial estimates of the size of Vanth from thermal measurements (Brown et al. 2010; Fornasier et al. 2013) are approximately 280 km, with an albedo of approximately 0.25. Later observations of Orcus/Vanth made with ALMA give a diameter for Vanth of 475 75 km, with an albedo of 0.08 0.02 (Brown & Butler 2018). Our occultation measurement agrees with this new measurement for Vanth's size, and further constrains the size. Vanth is therefore darker than Orcus, implying either a difference in origin or in subsequent evolution. As reported in Sickafoose et al. (2018, submitted), neither atmosphere nor rings were detected in the occultation data.
  38. Kiss, C., Marton, G., Parker, A., et al., (including Grundy, W.), 2018, DPS, 50, 311.02, The mass and density of the dwarf planet 2007 OR10
    The satellite of 2007 OR10 was discovered on archival Hubble Space Telescope images in 2017. With new observations taken with the WFC3 camera of the HST in late 2017 we were able to confirm the presence of the satellite and determine the orbit. The orbit's notable eccentricity, e=0.31, may be a consequence of an intrinsically eccentric orbit and slow tidal evolution, but may also be caused by the Kozai mechanism. Dynamical considerations also suggest that the moon is small, D < 100 km. Based on the newly determined system mass of 1.751021kg, 2007 O10 is the fifth most massive dwarf planet after Eris, Pluto, Haumea and Makemake. We also revisited the radiometric size estimate of the primary using the assumption that the moon orbits in the equatorial plane of the primary. This approach provides a size range of 1210 km < D < 1295 km, and a bulk density of 1.720.16 g cm-3 for the primary. A previous size estimate that had assumed an equator-on configuration (D = 1535+75-225 km) provides a density of 0.92-0.14+0.46 g cm-3, unexpectedly low for a 1000 km-sized dwarf planet. 2007 OR10 and the satellite have the larest color difference, (V-R)=0.430.17 among binary transneptunian objects.
  39. Weaver, H., Porter, S., Spencer, J., et al., (including Grundy, W.), 2018, DPS, 50, 311.03, Searches for KBO Binaries using New Horizons LORRI
    The New Horizons (NH) spacecraft is currently traversing the densest portion of the Kuiper belt (r 43 AU), enabling observations of known Kuiper belt objects (KBOs) at unique geometries, including at large phase angles not possible from the inner solar system and at ranges that provide higher spatial resolution than available from Earth, or Earth-orbiting, facilities. New Horizons carries a large aperture (20.8 cm) visible light imaging system, the LOng Range Reconnaissance Imager (LORRI), whose resolution (IFOV=1,4 arcsec for 1x1 and 4x4 modes, respectively) permits searches for binaries at finer spatial scales than available from the Hubble Space Telescope (HST). We have already scheduled observations of 13 KBOs (1 Plutino, 1 Hot Classical, 1 Scattered Disk, and 10 Cold Classicals) that pass within 1 AU of the NH spacecraft, and we are actively searching for additional candidates using ground-based telescopes. Five of the KBOs pass within 0.2 AU of the NH spacecraft, including two with ranges of 0.1 AU (73 km/pix for 1x1 mode). LORRI's photometric sensitivity for these satellite searches (V 16.3 in 1x1 mode after co-adding 125 0.5s exposures; V 21 in 4x4 mode after co-adding 50 30s exposures) is comparable to, or exceeds, that available from HST. Five of the six highest resolution (1x1 mode) NH KBO satellite searches are being conducted during the latter half of 2018, although most of the data will not be downlinked to Earth until 2019. Here we report on the binary search limits achieved for the five NH distant KBO observations already obtained and our plans for the upcoming searches.
  40. Tegler, S., Stufflebeam, T., Grundy, W., et al., (including Hanley, J.), 2018, DPS, 50, 311.05, A New, Unusual, and Diagnostic Band in Near-Infrared Spectra of Laboratory Ice Samples and Triton
    We present near-infrared spectra of carbon monoxide (CO) and nitrogen (N2) ice mixtures obtained in the Northern Arizona University Astrophysical Ice Laboratory. We confirm the existence of an unidentified band at 4466 cm-1 (2.239 m) in these mixtures that was first reported by Quirico and Schmitt (1997, Icarus, 128, 181-188). A systematic laboratory study of the band has led us to some surprising results. Specifically, the band is strongest for a sample with near equal amounts of CO and N2; however, the band is not present in a pure CO ice sample nor a pure N2 ice sample. Nor is the band present in a CO and argon (Ar) mixture. Furthermore, the 2.239 m band shifts for 13CO in an N2 ice sample and for C18O in an N2 ice sample, but not for 12C16O in a 14N2 enriched (15N14N depleted) ice sample. We looked into the solid state phase behavior of the mixtures, and found CO and N2 are fully miscible in one another. We mapped the temperature and composition dependence of the alpha - beta N2 phase transition and found the band in both N2 phases. Our experiments suggest the band arises from some sort of interaction between individual CO and N2 molecules in the solid state. In addition to laboratory spectra, we present a recently obtained near-infrared spectrum of Triton taken with the 8-meter Gemini Telescope in Chile and the IGRINS spectrograph. The 2.239 m band weakly appears in the spectrum. Besides laboratory and telescope spectra, we present the results of our theoretical efforts to better understand the interaction between the CO and N2 molecules giving rise to this band. Our work shows the 2.239 m band has important applications for remote sensing of icy outer system objects. In particular, its detection on icy bodies like Triton, and perhaps future detections on Pluto, Eris, and Makemake, demonstrates the CO and N2 molecules are intimately mixed together. Perhaps spectrographs on future spacecraft could exploit this band to better understand the chemical makeup of the ice on this class of bodies.
  41. Murray, K., Holler, B., Grundy, W., 2018, DPS, 50, 311.08, Search for a Pluto-like Satellite System Around Eris
    The most massive trans-Neptunian object, (136199) Eris, has one known satellite, Dysnomia. While some uncertainty surrounds the origin of Dysnomia, the favored mechanism for the formation of satellites among the large trans-Neptunian objects is giant impacts. Numerical modeling strongly favors the formation of the Pluto system by giant impact, and the system contains one large satellite, Charon, as well as four smaller satellites orbiting in near mean-motion resonances with Charon. The existence of minor satellites in the Eris/Dysnomia system was examined using images obtained with WFC3/HST in January and February 2018 (program 15171). These images were taken through the F606W filter and visits were scheduled to capture Dysnomia at different orbital phases. Aperture photometry was performed on Eris and a synthetic PSF inserted into median-stacked images from each orbit to determine the detection limit for a hypothetical minor satellite. We find that we are able to detect objects 9.70.2 magnitudes fainter than Eris at the 3- level. We assumed that any potential minor satellites would orbit in the same plane as Dysnomia and projected orbits for hypothetical satellites in mean-motion resonance with Dysnomia onto each image. Aperture photometry, centered on each pixel that fell on the projected orbit paths, was performed to search for 3- outliers. We then compared the position of the outliers across multiple images to determine if the motion is what would be expected for a satellite on that orbit. This method is also applicable for minor satellite searches in other large TNO binary systems.
  42. McAdam, M., Mommert, M., Trilling, D., 2018, DPS, 50, 312.01, Archived Spitzer Observations of (3200) Phaethon: an aqueously altered asteroid.
    (3200) Phaethon is a perplexing object. It is the progenitor of the Geminids meteor stream, yet activity observed at perihelion is not sufficient to be the sole source of the meteors observed at Earth (e.g.,[1], [2]). It has been argued that Phaethon has a cometary origin but has been degassed due to many close solar passages (e.g., [3]). Phaethon has also been suggested to be related to asteroids based on near-infrared spectral similarity (e.g., [4]) and dynamical association between Phaethon's orbit and (2) Pallas (e.g., [5]). Here we present archived, mid-infrared Spitzer spectroscopy of (3200) Phaethon to investigate if Phaethon is spectrally similar to cometary nuclei or asteroids. Phaethon was observed by Spitzer with the IRS instrument on January 14, 2005 using the short-low and long-low modes of the IRS instrument with wavelength ranges of 5.5-13.2-m and 14.0-38-m, respectively. The integration time was 58.7 s. Its heliocentric distance was 1.1 AU and distance from Earth was 0.7 AU with a phase angle of 60.3 degrees. We first fit Phaethon's infrared spectrum with the Near Earth Asteroid Thermal Model [6] finding a best fit diameter of 7.4 +/-0.79 km, an albedo of 0.041(+0.003, -0.004) and an eta parameter of 2.30 (+0.05, -0.04). Cometary nuclei are known to have distinct spectral signatures from asteroids in the mid-infrared (especially between 5.5-13.2-mm; e.g., [7]). Phaethon appears to be asteroid-like in this wavelength region, lacking the characteristic cometary spectral signature. Furthermore, we find that Phaethon appears to be most similar to intermediately altered carbonaceous chondrites in the CM and CI chemical groups. This indicates that Phaethon has 75-80% hydrated minerals on its surface, despite frequent close passages to the Sun. References: [1] Li, J., & Jewitt, D. (2013). AJ, 145(6), 154. [2] Hui, M. T., & Li, J. (2016). AJ,153(1), 23. [3] Fox, K., et al (1984). MNRAS, 208(1), 11P-15P. [4] Licandro, J. et al., (2007). A&A, 461(2), 751-757. [5] de Leon, J., et al., (2010). A&A 513, A26. [6] Harris, A. W. (1998). Icarus, 131(2), 291-301. [7] Kelley, M. S., (2017). Icarus, 284, 344-358.
  43. Magnuson, M., Moskovitz, N., Devogele, M., et al., (including Thirouin, A., Skiff, B., Mommert, M., Burt, B.), 2018, DPS, 50, 312.07, The Mission Accessible Near Earth Object Survey (MANOS): Spectrophotometric Characterization of Small NEOs
    The Mission Accessible Near Earth Object Survey (MANOS) Spectrophotometric Characterization of Small NEOs The Mission Accessible Near Earth Object Survey (MANOS) was designed to characterize sub-km, low delta-v, newly discovered near-Earth objects (NEOs). A subset of MANOS includes collecting color photometry in the Sloan Digital Sky Survey (SDSS) filter set, which can be used to produce rough taxonomic assignments for our targets. Such information is critical for (1) understanding how the Solar System formed as NEOs are remnants from the epoch of planet formation, (2) the interpretation of meteorites as NEOs are their primary producers, and (3), resource extraction missions in space; which are soon to become reality with future manned missions expected to extend beyond low earth orbit. MANOS utilizes 4-m (Lowell Observatory's Discovery Channel Telescope, SOAR) and 8-m (Gemini North and South) telescopes which enables traditional spectroscopy down to an apparent visual magnitude of 19.5 and 20.5 respectively. The NEOs observed by MANOS have an average absolute magnitude of H > 21, corresponding to objects with a mean diameter in the 100m range. These relatively small targets are most often discovered near peak brightness around V 20-21 mag, with follow up observations during subsequent apparitions being infeasible as targets return on average 100 times fainter (Galache et al. 2015). By performing coarse spectrophotometry, we are offered a unique opportunity to characterize particularly small NEOs, a currently under sampled portion of the NEO population. Our comprehensive data set contains spectrophotometric results for over 100 targets. These data will be compared to the Sloan Digital Sky Survey Moving Object Catalog, which contains a similar size sample of km-scale NEOs. It is understood that while more than 80% of meteorites have origins traced to S-type asteroids (Harvey & Cassidy 1989), only 60% of the large NEOs are designated as such (Binzel et al. 2018). Our sample bridges the gap between meteorites and large NEOs, and thus can provide insight into this discrepancy. This work is supported by the NASA NEOO program, grant number NNX17AH06G.
  44. Earle, A., Grundy, W., Howett, C., et al., 2018, DPS, 50, 314.02, The highest spatial resolution compositional maps of Pluto and what they tell us about surface composition and geology
    NASA's New Horizons spacecraft has given us an unprecedented, detailed look at the Pluto system. New Horizons' Ralph/MVIC (Multispectral Visible Imaging Camera) is composed of 7 independent CCD arrays on a single substrate, including a red channel (540-700 nm), near-infrared channel (780-975 nm), and a methane channel (860-910 nm). The ratios of these channels were compared to produce high-resolution methane equivalent width (E.W.) (based on the 890 nm band) and spectral slope maps of Pluto's surface (originally published in Earle et al., 2018. DOI: 10.1016/j.icarus.2018.06.005). These maps provide a means for quantitatively studying the relationships between methane distribution, surface redness, latitude, elevation, and geology. Earle et al. 2018 explored the global trends between latitude, elevation, and surface composition, finding that MVIC E.W. showed dependence on both latitude and elevation (with the broadest MVIC E.W.s appearing near the equator and at altitudes greater than 2 km), while redness showed some relationships with latitude but very little dependence on elevation. It was also noted that in addition to the global trends, there appeared to be complex, smaller-scale relationships between surface composition and geologic features, like craters and mountains. In this talk we will build on the work of Earle et al. 2018 by taking a deeper, quantitative look at the localized trends that occur between surface composition and geologic features on Pluto's surface. We will also look at how topography can affect the local insolation over various timescales leading up to the New Horizons observations of Pluto and consider how this influences the volatile distribution and could potentially be used to constrain the timescales over which volatile transport occurs.
  45. Levine, S., Henden, A., Terrell, D., et al., 2018, DPS, 50, 315.03, Applications of the AAVSO Photometric All-Sky Survey (APASS) to observations of objects in our Solar System
    The AAVSO Photometric All-Sky Survey (APASS) is designed to provide photometric standards over the entire sky in the magnitude range 6.5 < V < 17.5mag in B, V, u, g, r, i, z and Y filter passbands. For the magnitude range, APASS is well matched to optical telescopes from 8-cm up to 2- to 3-meters in diameter. The survey was originally conceived to facilitate variable star observations. However, having photometric standards in every image taken can be of great utility to the Solar System community as well. Not only does this make it easier to combine extended time series photometry of observations of objects like asteroid and comets that move appreciably, it also makes it possible to recover photometry at the few percent level for data taken under non-photometric conditions (e.g. as demonstrated with SDSS data by Ivezic et al 2007, AJ, 134, 973). APASS data have been taken between 2010 and 2018 with twin ASA 20-cm astrographs installed at northern and southern hemisphere sites. Over the course of the survey, we have accummulated over 500,000 images, each 2.8 x 2.8 degrees in size. We present initial results of our work to compile a catalogue of all the serendipitous observations of asteroids and comets in those images. For the bulk of the survey data, we have contemporaneous five color (B,V,g,r,i) imaging.
  46. McNeill, A., Hora, J., Gustafsson, A., et al., (including Mommert, M.), 2018, DPS, 50, 401.05, Near Earth Object studies from the Spitzer Space Telescope
    We present an overview of the Near Earth Object (NEO) studies carried out using IRAC on the Spitzer Space Telescope. Over 2000 NEOs have been observed in several programs since the start of the Spitzer Warm Mission. Thermal modelling has been used to estimate the albedos and diameters of the NEOs. In the absence of dense photometry for a large population of NEOs, the best method of obtaining a shape distribution comes from sparse photometry and partial lightcurves. We have used 824 partial lightcurves obtained by Spitzer to determine a shape distribution for NEOs. From this data we find a best fit average elongation \frac{b}{a}=0.72 \pm 0.08. We compare this result with a distribution obtained from Pan-STARRS 1 and find it to be in excellent agreement. We also derive periods and amplitudes for a subset of 38 NEOs, many of them having no previously reported rotation periods. For objects where the period observed did not sample the full rotational period, we derived lower limits to these parameters. We also identify an object with rapid spin and diameter D = 519^{+227}_{-116} m and find that for this object a cohesive strength of about 225 Pa is necessary to avoid fission. Major NEO surveys return a small fraction of high albedo objects which do not have clear analogs in the current meteorite population. About 10% of Spitzer-observed NEOs have nominal albedo solutions greater than 0.5. This may be a result of lightcurve variability leading to an incorrect estimate of diameter or inaccurate absolute visual magnitudes. We performed a Monte Carlo analysis on 1500 NEOs observed by Spitzer, sampling the visible and thermal fluxes of all targets in an amplitude range of 0.1 to 1.0 magnitudes to hold the high albedo targets within albedo cutoffs of 0.4, 0.5, and 0.6. Our results suggest that an amplitude of >1.0 magnitudes is required to duplicate the observations. Implementing the mean lightcurve amplitude obtained from the shape distribution we obtained, we provide an upper-limit on the geometric albedo based on composition.
  47. Hsieh, H., Ishiguro, M., Knight, M., et al., (including Moskovitz, N.), 2018, DPS, 50, 408.06, The Reactivation and Nucleus Characterization of Main-Belt Comet 358P/PANSTARRS (P/2012 T1)
    We present observations of main-belt comet 358P/PANSTARRS (P/2012 T1) obtained using the Gemini South telescope from 2017 July to 2017 December (Gemini program IDs GS-2017A-LP-11 and GS-2017B-LP-11), as the object approached perihelion for the first time since its discovery. We find best-fit IAU phase function parameters of H_R=19.5+/-0.2 mag and G_R=-0.22+/-0.13 for the nucleus, corresponding to an effective radius of r_N=0.32+/-0.03 km (assuming an albedo of p_R=0.05). The object appears significantly brighter (by >1 mag) than expected starting in 2017 November, while a faint dust tail oriented approximately in the antisolar direction is also observed on 2017 December 18. We conclude that 358P has become active again for the first time since its previously observed active period in 2012-2013. These observations make 358P the seventh main-belt comet candidate confirmed to exhibit recurrent activity near perihelion with intervening inactivity away from perihelion, strongly indicating that its activity is sublimation-driven. Fitting a linear function to the ejected dust masses inferred for 358P in 2017 when it is apparently active, we find an average net dust production rate of 2.0+/-0.6 kg/s (assuming a mean effective particle radius of a_d=1 mm) and an estimated activity start date of 2017 November 8+/-4 when the object was at a true anomaly of 316+/-1 degrees and a heliocentric distance of R=2.54 AU. This work has been published in Hsieh et al. (2018, AJ, 156, 39). We will also present new observations of the object obtained after the submission of this abstract from 2018 August through 2018 October (Gemini program ID GS-2018B-LP-11), during which its previously-observed activity is expected to continue, and report whether we find any evidence of changes in activity strength between the object's 2012-2013 and 2017 active periods. The authors acknowledge support from NASA Solar System Observations grant NNX16AD68G and the State of Arizona Technology and Research Initiative Program.
  48. Moskovitz, N., Schottland, R., Burt, B., et al., (including Wasserman, L.), 2018, DPS, 50, 408.08, astorb at Lowell Observatory: A comprehensive system to enable asteroid science
    astorb is a database of orbital elements for all known asteroids in the Solar System (780,489 objects as of 12 July 2018), has been hosted at Lowell Observatory for over 20 years, and is actively curated to be automatically updated as new objects are discovered. Front-end access to the database and associated tools are available at asteroid.lowell.edu. Modernization and upgrades to the astorb system are ongoing with expected completion by mid-2019. Upgrades currently implemented include the addition of physical properties, such as albedo and rotation period, and redesigned observational planning tools, such as ephemeris and finder chart generators. Data on physical properties are pulled from multiple sources including NASA's Planetary Data System (PDS), the asteroid Lightcurve Database (LCDB), and a number of project-specific online compilations. Future upgrades will include additional physical properties, enhanced query capabilities, and a system for credentialed user input to the database as a way to facilitate rapid dissemination of observational results. User feedback on desired additional functionality is invited. The combination of physical properties and tools for observational prediction provides a powerful system for planning and conducting new science investigations. Through queries that execute in just a few seconds we can answer complex questions such as: which members of the Vesta dynamical family have measured albedos and are observable tonight? what is the lowest numbered asteroid without a measured albedo and when is it next observable? which Main Belt asteroids with known spectral types are passing through opposition this week? These examples highlight the type of queries for which astorb is optimized. We will present the current state of the astorb system and highlight some of the novel tools available to the community. This work is supported by the NASA PDART program, grant number NNX16AG52G.
  49. Person, M., Schindler, K., Bosh, A., et al., (including Levine, S.), 2018, DPS, 50, 416.10, Airborne and Ground Observations of the Stellar Occultation by Triton on 5 October 2017
    On 5 October 2017, Triton occulted the 13th magnitude star UCAC4 410-143659 as seen from the Eastern US, North Atlantic, and Europe. Our collaboration observed this event from the Stratospheric Observatory for Infrared Astronomy (SOFIA) aircraft, as well as numerous (over two dozen) ground stations throughout the US and Europe. Here, we present the preliminary results of analyzing this dataset and highlight a number of features of Triton's atmosphere. Initial reduction of the data indicates that the atmospheric pressure increases seen throughout the 90's have stabilized or perhaps begun to reverse, as the current pressures are more comparable to those measured during the earlier occultations of the 1990's than the later ones, although still greater than the pressure observed by Voyager 2 in 1989. Careful calibration of the multi-wavelength observations made from SOFIA indicates a clear atmosphere at the levels to which we are sensitive (>35 km), with no signs of the various particulate dust plumes or cloud-like structures seen by Voyager 2 below 8 km altitude. Data reduction is progressing and a final report is in preparation.
  50. Erasmus, N., McNeill, A., Mommert, M., et al., 2018, DPS, 50, 417.07, Physical Properties of 2000 Observed Main-Belt Asteroids
    We present VRI spectrophotometry of 2238 main-belt asteroids (MBAs) observed with the Sutherland, South Africa node of the Korea Microlensing Telescope Network (KMTNet). Through our broadband spectrophotometry we are able to reliably distinguish among four asteroid taxonomies: S-, C-, X-, or D-type asteroids. We categorize 1964 of the 2238 observed targets as either a S-, C-, X-, or D-type asteroid by means of a machine learning algorithm that was trained with colors synthesized from spectra of observed MIT-UH-IRTF targets that have confidently identified taxonomies. Additionally, we report 0.35-5.5 hr (mean: 3.0 hr) light-curve data for each MBA which allowed us to resolve the complete rotation periods and amplitudes for 1/5th of our targets. Of the 400 targets with resolved rotation periods, 3 have rotation periods potentially below the theoretical zero-cohesion boundary limit of 2.2 hr. Using our determined taxonomies and rotation properties we also show preliminary results of further investigation into MBA family and non-family members within our target list.
  51. Sickafoose, A., Levine, S., Bosh, A., et al., 2018, DPS, 50, 502.02, Pluto's atmosphere after New Horizons: results from stellar occultations in 2017 and 2018
    Stellar occultations have been employed for the last thirty years to characterize Pluto's atmosphere. The atmospheric pressure has increased between 1988 and 2015 (e.g. Bosh et al. 2013; Sicardy et al. 2015). Evolution in the shape of the occultation light curves over time has revealed waves in the upper atmosphere (e.g. Hubbard et al. 2009; Person et al. 2008) and suggests a thermal gradient, possibly combined with extinction-generating events, in the lower atmosphere (e.g. Elliot et al. 2007; Olkin et al. 2014). Occultation data have been combined with volatile transport models (Hansen & Paige 1996; Young 2013) to predict Pluto's atmospheric properties during and beyond the 2015 flyby of NASA's New Horizons spacecraft. Some models indicate that Pluto's atmosphere should collapse over a relatively short timescale; however, recent results are consistent with models that have no atmospheric collapse, stemming from high thermal inertia and a permanent, northern cap (e.g. Olkin et al. 2015). Here, we report results from two stellar occultations by Pluto, in 2017 and 2018. A single chord was observed at each epoch. The first occultation was on 2017 August 07, with a shadow path over the Pacific Ocean. The star had visible magnitude of 14.5, with relative velocity of 20.8 km s-1. Observations were taken from NASA's 3-m Infrared Telescope Facility in Hawaii. The dataset includes 2.5-second, visible-wavelength images from MORIS (MIT Optical Rapid Imaging System), and low-resolution, near-infrared spectra from SpeX with 3-second integration time. The second occultation was on 2018 April 09, with a shadow path over the western United States. The star had visible magnitude of 17.9, with relative velocity of 6.4 km s-1. Visible-wavelength images, at 10 Hz, were taken from the 4.3-m Discovery Channel Telescope in Arizona with a POETS (Portable Occultation Eclipse and Transit System). The 2018 observation was central, with half-light to half-light chord length of 2280 km. The 2017 observation had half-light to half-light chord length of 1650 km. The shape of both light curves is indicative of a body with an atmosphere. We present results for atmospheric model fits to these light curves and place them in context.
  52. Butler, B., Grundy, W., Gurwell, M., et al., 2018, DPS, 50, 502.06, Resolved Thermal Images of Pluto and Charon with ALMA
    We report on the first Earth-based observations of thermal emission from the surfaces of Pluto and Charon where the disks of each body are resolved. Observations at a wavelength of 1.2 mm were completed using the Atacama Large Millimeter/submillimeter Array (ALMA) on September 27 and 29, and October 14, 2017. The resolution of the observations was approximately 20 masec, while the sizes of Pluto and Charon were approximately 100 and 50 masec respectively, so both bodies were well-resolved individually. We have previously reported on observations from ALMA, the Submillimeter Array (SMA), and the Karl G. Jansky Very Large Array (VLA) where the two bodies are resolved from each other at these long wavelengths [1-4], but these are the first observations where the bodies are each resolved themselves. We know from New Horizons that both bodies have distinct surface features and ices which should result in temperature variations [5], and we will be able to correlate these with our thermal images. We note that our resolution is similar to that of the HST ACS and FOC maps, which were used to derive surface properties across both bodies [6]. We will also be able to derive disk-averaged brightness temperatures, which we can compare with our previous results: brightness temperatures of 33.0 K for Pluto and 43.5 K for Charon at these wavelengths. These low brightness temperatures, along with those from other icy bodies, have been examined in [7]. [1] Butler et al. 2015, BAAS #47, id.210.04. [2] Gurwell et al. 2011, DPS/EPSC, p271. [3] Butler et al. 2011, DPS/EPSC, p. 1670. [4] Butler et al. 2017 BAAS #49, id.102.02. [5] Schmitt et al. 2017, Icarus, 287, p.229. [6] Buie et al. 2010, AJ, 139, p.1128. [7] Lellouch et al. 2017, A&A, 608, id.A45.
  53. Mommert, M., Trilling, D., Knight, M., et al., (including Wainscoat, R., Harrington, O.), 2018, DPS, 50, 505.05, Systematic Characterization and Monitoring of Potentially Active Asteroids: The Case of Don Quixote
    Over the previous decades, activity has been observed in about 20 Solar System small bodies that were until then known as asteroids. Activation mechanisms have been proposed for these objects, including the sublimation of volatiles, rotational instability, and recent impacts; all these mechanisms provide strong constraints on the physical properties and evolution of these objects. The identification of more active asteroids will improve our understanding of the processes triggering activity as well the nature of asteroids in general. We present first results from our "Systematic Characterization and Monitoring of Potentially Active Asteroids" program, which obtains BVRI colors and performs V-band photometric monitoring of a sample of 103 dormant comet candidates and 10 near-Sun asteroids. The goal of this program is to find activity in and provide a spectrophotometric taxonomic classification for our targets in order to place limits on the volatile contents of these potentially active populations and improve our understanding of their evolution. We present the case of near-Earth asteroid (3552) Don Quixote in which we discovered activity in multiple wavelength regimes. In October 2017 we observed activity using Spitzer Space Telescope observations that agrees with findings by Mommert et al. (2014, ApJ 781), suggesting continuous activity from the sublimation of CO or CO2. While close in time optical observations did not reveal any dust activity, observations in March 2018 revealed for the first time episodic dust activity in this object (Mommert et al., 2018, CBET 4502). Follow-up observations in June 2018 with the 30m IRAM sub-millimeter telescope show a lack of emission from the CO(2-1) line and hence suggest that activity in this object is most likely triggered by the sublimation of CO2. Our observations suggest that Don Quixote is most likely a weakly active CO2-rich comet. The finding of faint activity in Don Quixote underscores the necessity of a systematic monitoring campaign to find activity. This program is based upon work supported by NASA under Grant No. NNX17AG88G.
  54. Protopapa, S., Cruikshank, D., Dalle Ore, C., et al., (including Grundy, W.), 2018, DPS, 50, 506.01, Are multiple coloring agents present across the surface of Pluto and its large satellite Charon?
    The New Horizons flyby of Pluto has revealed a complex world rich in a variety of landforms, colors, and compositions (Stern et al., 2015). The color imaging of Pluto's encounter hemisphere obtained by the Multi-spectral Visible Imaging Camera (MVIC) component of the Ralph instrument (Reuter et al., 2008) displays a latitude-dependent distribution of colors ranging from dark red to yellow (Olkin et al., 2017). Laboratory experiments suggest that Pluto's coloration may be due to the presence on the surface of tholin-like materials, which are organic compounds produced through photolysis and radiolysis of native material found on the surface and atmosphere of the dwarf planet. Tholins produced in the laboratory exhibit a wide range of colors (Materese et al., 2015; Cruikshank et al., 2016). Pluto's largest moon Charon displays distinctly reddish tholin coloration around its north pole (Grundy et al. 2016a). Grundy et al. 2016b put forth the idea that this might be the result of gas from Pluto transiently cold-trapped and processed at Charon's winter pole. The true contribution of the coloring agents cannot be assessed without consideration of the visible spectral domain as in Protopapa et al. (2017). This is due to the fact that the diagnostic spectral signature of tholins is a strong red slope in the visible part of the spectrum. We present a characterization of the tholin material across the surface of Pluto and its moon Charon through radiative transfer modeling of the New Horizons Ralph/LEISA (Linear Etalon Imaging Spectral Array, infrared spectrometer) and MVIC data. We compare our findings with optical constants of Pluto tholin we compute from laboratory reflectance measurements by Materese et al. (2015). The ultimate goal is understanding the variety of tholins on the surface of Pluto and Charon, and the processes responsible for their formation and distribution.
  55. Schmitt, B., Gabasova, L., Philippe, S., et al., (including Grundy, W.), 2018, DPS, 50, 506.02, Evidence of local CH4 stratification on Pluto from New Horisons LEISA data and a complete N2 ice map.
    The diurnal, seasonal and astronomical cycles on Pluto trigger sublimation-transport-condensation cycles of the volatile ices (N2, CH4, CO) with different amplitudes and time constants at the surface. The qualitative distribution of the two major volatile ice phases identified on the surface of Pluto, N2-rich:CH4:CO ice and CH4-rich ice, has been mapped by Schmitt et al. (2017) and the spatial transitions between the predominant zone of these phases have been highlighted. The first quantitative composition map has been derived by Protopapa et al. (2017). A surprising observation, but not discussed in Schmitt et al. paper, was that the CH4 qualitative abundance maps obtained from different CH4 bands display relatively different spatial distributions, but with regular evolutions at a given location from the weakest to the strongest CH4 bands. In this talk we demonstrate that these band depth changes reflect a stratification of CH4, either in the CH4 concentration in N2-rich ice and/or in the relative abundance between the N2-rich:CH4:CO and CH4-rich ices, depending on the area. For this we use in addition our 'CH4 state index' based on the spectral position of the CH4 bands and a new N2 ice distribution map including the area where the N2 ice band is too weak to be observed directly. The stratification of CH4 is shown to result from the differential sublimation between N2 and CH4 which tends to concentrate CH4 in N2 ice grains and, according to the phase diagram, produces a CH4-rich phase that accumulates on the surface. We will show that several different configurations appear to exist at the surface of Pluto according to the latitude and the altitude, and that they may be the witness of different stages in the sublimation-condensation cycles or of different timescales. The occurence, the CH4 concentration and the depth of these stratified terrains can be correlated with the nitrogen sublimation fluxes obtained by volatile transport models (Bertrand et al. 2018).
  56. Singer, K., Schenk, P., McKinnon, W., et al., (including Grundy, W.), 2018, DPS, 50, 506.04, Cryovolcanic Constructs on Pluto
    Pluto's surface has experienced considerable endogenic and exogenic resurfacing [1]. The terrains on Pluto represent a variety of ages, from seemingly ancient to surprisingly young. Some of the very young terrains are the result of the volatile ices on Pluto's surface (e.g., the convecting nitrogen-ice-rich plains of Sputnik Planitia). But Pluto also has several examples of more recent activity (terrains with few-to-no superimposed craters), that appear to be primarily made out of non-volatile water ice. The most prominent examples of potential cryovolcanism are two enormous topographic constructs with wide, deep central depressions [2]. The informally named Wright Mons stands 4 km high and the main mound spans 150 km. The informally named Piccard Mons is 7 km high and 225 km wide. The central depressions are dissimilar from a typical terrestrial shield volcano in that they are much wider (e.g., the Wright Mons central depression is 40-45 km wide, taking up 1/3rd of the total feature width) and deeper (the floors extend down to or below the level of the surrounding terrain). The central depression of Wright does not exhibit wall terraces that are typical indicators of collapse in terrestrial volcanoes. Instead, the central depression walls and floor have a large-scale hummocky texture similar to that the exterior of Wright, with individual hummocks on average 8-10 km across. A few terrains around Wright may be older, more fractured or cratered, examples of the terrain on the flanks. Thus there is some evidence for multiple episodes of terrain emplacement, but distinct flow fronts are not obvious. Each potential example of cryovolcanism found in the outer solar system is unique, and Pluto's features expand the information we have to understand this enigmatic process. We will present image, topographic, and composition data for Wright and Piccard along with geologic mapping results. We will discuss potential formation mechanisms in light of available empirical and model constraints. [1] Moore, J.M. et al. (2016) Science 351, 1284-1293. doi:10.1126/science.aad7055 [2] Singer, K.N. et al. (2016) Planetary Mappers Meeting 1920, #7017, http://adsabs.harvard.edu/abs/2016LPICo1920.7017S.
  57. Cruikshank, D., Umurhan, O., Moore, J., et al., (including Grundy, W.), 2018, DPS, 50, 506.05, Recent cryovolcanism on Pluto
    The Virgil Fossae region on Pluto exhibits three spatially coincident properties that are suggestive of recent cryovolcanic activity over an area approximately 300 by 200 km. Situated in the fossae channels and in the surrounding terrain are exposures of H2O ice in which there is entrained opaque red-colored matter of unknown composition. The H2O ice is also seen to carry spectral signatures at 1.65 and 2.2 m of NH3 in some form, possibly as a hydrate, an ammoniated salt, or some other compound. High-resolution images from the New Horizons spacecraft provide a base map upon which a map of H2O ice obtained at lower spatial resolution with the New Horizons LEISA mapping spectrometer is superimposed. Analysis of the LEISA map demonstrates that in areas where there is a minimal amount of CH4 ice, the exposed H2O ice exhibits the maximum NH3 signature, localized in one end of the main channel of the fossae complex. The NH3-H2O is distributed in patterns suggesting flow of cryolava along the fossa floor and ejection of cryoclastics in ballistic trajectories well beyond the fossa channels. Muted topography (craters and fossae) may represent mantling by cryoclastic deposits that also bear the NH3 signature in H2O ice and the red color. We present a model of the flow of a cryogenic magma emerging from sources in Virgil Fossa indicating that the extent of the flow can be several km. The appearance of the frozen magma over the full length (>200 km) of the main channel in the Virgil Fossae complex and extending through the north rim of Elliot crater and varying in elevation over a range of 2km, suggests that it emerged from multiple sources, probably along the length of the strike direction of the normal fault(s) defining the graben. The source or sources of the ammoniated H2O are one or more subsurface reservoirs that may or may not connect to the putative global ocean postulated for Pluto's interior. In a separate study in which we take the red-colored matter to be a complex organic tholin, we show that the chemistry in such a mixture is likely to produce amino acids and many nucleobases, including the five used in terrestrial biological systems (Cruikshank et al., submitted).
  58. Pendleton, Y., Cruikshank, D., Materese, C., et al., (including Grundy, W.), 2018, DPS, 50, 506.06, Prebiotic Chemistry of Pluto
    The variety of surface colors on Pluto results from the synthesis of complex organics in the atmosphere and on the surface. There is new evidence that tholins and other organics from a subsurface aquifer were carried to the surface by ammoniated liquid water to form deposits of unique color and chemical properties. Pluto's Virgil Fossae exhibits an exposure of H2O-NH3 ice and a uniquely red color that may contain tholins produced in such a subsurface environment. Geological evidence in images from the NASA New Horizons spacecraft supports the view that ammoniated water carrying a uniquely colored red tholin-like material emanated from one or more sources from a part of Virgil Fossae. Emission from these sources appears to have progressed along parts of the fossae before freezing upon contact with the vacuum and cold solid surface. In addition, material may have traveled on ballistic trajectories for >100 km. Pluto's organic tholins and ices, when viewed in the context of laboratory syntheses of complex molecules of prebiological importance, lead to a deeper understanding of the plausible chemistry that may be occurring on icy bodies in the outer Solar System. Compounds such as nucleobases, including those of biological significance, may have formed on the surface from UV irradiation of nitrogen-rich tholins ejected with warm subsurface water in cryovolcanic events. Alternatively, these complex molecules may have formed in subsurface fluid that emerged in and around Virgil Fossae. Laboratory irradiation of ice mixtures reflecting Pluto's composition have produced strongly colored complex organics including possible aromatic molecules. Recent experiments with pyrimidine and purines frozen in H2O-NH3 ice resulted in the formation of numerous nucleobases, including the biologically relevant guanine, cytosine, adenine, uracil, and thymine (Materese et al. 2017 Astrobiology 17, 761). It is also possible that some of the oldest organics on Pluto derive from the material inherited prior to the formation of the planet. Thus, geological processes recently revealing buried tholins on Pluto may be unveiling organics of either early Solar System legacy or interior processes within Pluto.
  59. Stansberry, J., Young, L., Lunine, J., et al., (including Grundy, W.), 2018, DPS, 50, 506.07, Long-term Evolution of Sputnik Planitia: Cryo-clastic Eruptions and their Implications
    The Sputnik Planitia (SP) impact basin [1] on Pluto is currently the location of an extensive deposit of volatile ices of N2, CO and CH4 [2]. Those ices are undergoing solid-state convection as evidenced by the organization of surface features into cellular structures tens of kilometers across [3, 4]. SP is a positive mass anomaly that migrated to its current position after a process of and sub-basin crustal thinning and volatile infilling [1, 5]. This scenario neglects the potentially important effects of endogenic heat flow, especially as might be enhanced due buried heat from the impact. Such upward heat flow would delay infilling of SP with volatile ices, and could result in interspersed episodes of infilling and removal of volatile material. The volatile ices would form an insulating layer, and the basal temperature (and corresponding vapor pressure of the N2 ice) would increase as the layer depth increased. For a heat-flow enhancement of just 5x over present-day endogenic heat flow, the vapor pressure of N2 will exceed the overburden stress at depths less than 1km. Such overpressure at the base of a nascent SP volatile-ice layer would lead to geyser-like activity and depletion of the volatiles. Later, thicker ice layers could perhaps effectively confine the N2 vapor. Truly violent releases of material could result, yielding episodic increases in atmospheric bulk, and transport of liquid and solid material entrained in the gas flow (what might be termed a "cryo-clastic" eruption mechanism). Such eruptions would be significantly supersonic and have significant horizontal velocity components. As a result, the flows could travel ballistically over distances comparable to Pluto's radius before falling back to the surface. Geomorphic signatures should result, although examples of the resulting landforms may not exist on the other explored bodies of the solar system. One Plutonian landform that might have been formed via this mechanism is the bladed terrain of Tartarus Dorsa. References [1] Nimmo et al., Nature v540 (2016). [2] Grundy et al., Science v351 (2016). [3] Stern et al., Science v350 (2015). [4] McKinnon et al., Nature v534 (2016). [5] Keane et al., Nature v540 (2016).
  60. Beyer, R., Spencer, J., McKinnon, W., et al., (including Grundy, W.), 2018, DPS, 50, 506.08, The Nature and Origin of Charon's Smooth Plains
    Charon displays extensive plains that cover the equatorial area and south to the terminator on the sub-Pluto hemisphere observed by New Horizons. We hypothesize that these plains are a result of Charon's global extension and early subsurface ocean yielding a large cryoflow composed of mantle material that completely resurfaced this area leaving the plains and other features we that we observe today. The resurfacing of the plains is not the result of a singular eruptive or effusive center from which cryoflows spread out across the more than 400,000 square kilometers of Vulcan Planitia. We hypothesize that the resurfacing was the result of ammonia-rich cryo-material from the last stages of ocean freezing either buoyantly rising and flowing out on to the pre-Vulcan lowlands, or as a result of more severe disruption that resulted in crustal blocks foundering, and the buoyant, viscous cryo-material under those blocks rising up and spreading out. Under these hypotheses, there would be no singular effusive center, but the sources of the plains material would be in many places across the region, and as the material flowed across the pre-Vulcan lowlands or enveloped the foundering blocks, it would create an extensive plains unit. Geological observations, modeling of possible flow rheology, and an analysis of rille orientations support the conclusion that the extensive plains on Charon are a vast cryoflow emplaced unit, similar to those seen on Ariel and Miranda and possibly other icy worlds in the solar system. Charon fits into the panoply of icy satellites which display evidence for the movement of cryoflows and resurfacing.
  61. Devogele, M., Moskovitz, N., Thomas, C., et al., (including Thirouin, A., Mommert, M., Skiff, B.), 2018, DPS, 50, 508.01, The Mission Accessible Near-Earth Objects Survey (MANOS): First Results from the Visible Spectroscopic Survey
    The Mission Accessible Near-Earth Objects Survey (MANOS) started in August 2013 and is a multi-year survey supported by the National Optical Astronomy Observatory (NOAO) and Lowell Observatory, and funded by the NASA NEOO (Near-Earth Object Observations) program. It aims at characterizing sub-km, low delta-v (typically <7 km/s), Near-Earth Objects (NEOs) by collecting astrometry, lightcurve photometry, and reflectance spectra. The physical properties of NEOs are known to be size dependent. However, some open questions remain such as whether these objects are rubble piles or monolithic bodies, or whether they are covered by regolith. A compositional discrepancy between large NEOs (>1km) and meteorite collection is also observed (Stuart et al., 2004; Vernazza et al., 2008). Laboratory measurements have also shown that grain size can cause variation in spectral slope or absorption band depth (Cooper et al., 1999;Cloutis et al., 2013). The smallest NEOs can have rotation periods under 1 minute (Thirouin et al., 2016), while asteroids larger than 150m do not rotate faster than 2.2 hours. This supports the hypothesis of small asteroids being monolithic and structurally different than larger ones. We report here the first results from MANOS on the visible spectroscopic properties. We have analysed roughly 300 asteroids with a mean size around 80 meters (H 25), and with some targets as small as few meters (H=30). This represents one of the largest comprehensive spectroscopic datasets for NEOs < 100 meters. We will discuss the compositional properties of this sample relative to other NEOs (km and sub-km) (Perna et al., 2018; Thomas et al., 2011, and DeMeo et al., 2008), and to Main Belt asteroids (Bus et al., 2002 and DeMeo et al., 2009) and compare them with the meteorite population. All spectroscopic data have been reduced using a new python based pipeline for asteroid spectroscopic reduction developed to be easily portable to any visible spectrograph. The use of the same pipeline for all data obtained by this survey allows us to obtain a consistent data set of spectral properties of small NEOs. This work is supported by the NASA NEOO program, grant number NNX17AH06G.
  62. Navarro, S., Mommert, M., Trilling, D., et al., 2018, DPS, 50, 508.03, First multi-band results from the rapid-response spectrophotometric characterization of Near-Earth objects using RATIR
    We are carrying out a program to obtain rapid-response spectrophotometric characterization of newly discovered Near Earth Objects. Here we present a detailed analysis of the taxonomic distribution of about 100 small (tens to hundreds of meters in diameter) NEOs observed with the RATIR instrument on the 1.5-m telescope on San Pedro Martir, Mexico. The observations are made in queue mode using r, i, Y, Z, J, H bands, and the data processing is carried out autonomously. Using machine learning techniques and synthetic colors derived from measured asteroid spectra, we derive probabilistic taxonomic classifications for our targets. This work is part of a collaboration in which we will characterize hundreds of NEOs that are generally too faint for other characterization techniques (down to V 21). This work is supported by funding from NASA's Solar System Observations program.
  63. Gustafsson, A., Moskovitz, N., Knight, M., et al., (including Schleicher, D., Bida, T., Dunham, E.), 2018, DPS, 50, 508.10, Asteroid 3200 (Phaethon): Simultaneous Visible and Near-Infrared Observations
    The Near-Infrared High Throughput Spectrograph (NIHTS) is a low resolution spectrograph that operates from 0.86-2.4 microns on Lowell Observatory's 4.3-m Discovery Channel Telescope (DCT) in Happy Jack, AZ. Using a dichroic mirror which transmits visible wavelengths and reflects the near-infrared, we have the opportunity to operate the Large Monolithic Imager, an independent visible wavelength CCD, simultaneously with NIHTS. In combination with the premier non-sidereal tracking capabilities of the DCT, NIHTS is an extremely efficient instrument and is expected to make significant contributions to several areas of astronomy. We present an overview of the first NIHTS spectroscopic results which also employed simultaneous optical LMI imaging of asteroid 3200 (Phaethon). The unique active asteroid Phaethon, dynamically related to the parent body of the Geminid meteor shower (Whipple 1983), made a close approach to Earth in December 2017. The target passed within 0.07 AU and provided a rare opportunity to search for rotationally resolved compositional differences across the surface of the 5 km body. Phaethon is a B-type NEO (Bus and Binzel 2002), dynamically linked to Main-belt asteroid Pallas (2) (deLeon et al. 2010). Phaethon's dayside temperatures are 1000 K from solar radiation heating near perihelion at 0.14 AU (Jewitt 2010). As a result, the activity on the surface is unlikely a result of near-surface ice sublimation, but instead, a combination of thermal fracture, dehydration cracking, radiation pressure sweeping, and electrostatic effects (Jewitt 2010). Due to the mass loss that the object has undergone, it is hypothesized that the surface would show evidence of the effects of solar radiation through spectral reddening. We observed Phaethon before and after closest approach between December 14, 2017 and December 18, 2017 obtaining both near-infrared spectra with NIHTS and visible lightcurves with LMI in SDSS r' and a narrow-band Blue Continuum comet filter (4420-4500 A) centered at 4453 A. We report our time-resolved spectroscopic findings of this unique object. This work is supported in part by the NASA NEOO program, grant number NNX17AH06G.
  64. Parker, A., Buie, M., Grundy, W., et al., 2018, DPS, 50, 509.02, The Mass, Density, and Figure of the Kuiper Belt Dwarf Planet Makemake
    The recent discovery and subsequent orbital characterization of Makemake's satellite have provided a means to measure the mass of the dwarf planet for the first time. As Makemake is a fast rotator, it is expected to have a non-spherical equilibrium figure. If the orbital pole of the satellite is aligned with the spin pole of Makemake, then the spin pole is nearly orthogonal to the occultation chords presented in Ortiz et al. (2012). It is difficult to constrain the equatorial radius of a spheroid aligned in such a way; the resulting preferred volume and its uncertainty are larger than previous estimates. The preferred figure has a ratio of equatorial to polar diameters of 1.13. Combining this new figure estimate and the mass measurement of 3.1x1021 kg, we derive a relatively low density for Makemake of 1.7 g/cc; adopting the Brown (2013) volume estimate results in a higher density of 2.1 g/cc. In this presentation, we will describe the existing and upcoming Hubble Space Telescope observations of the system that enable these mass and orbit plane measurements, derivation of the mass, figure, and density of Makemake, and the implications for the internal structure of Makemake. We will also describe possible upcoming opportunities to observe mutual events between Makemake and its satellite.
  65. Holler, B., Grundy, W., Buie, M., et al., 2018, DPS, 50, 509.03, Breaking the degeneracy of Eris' pole orientation
    The most massive trans-Neptunian object, (136199) Eris, has one known satellite, Dysnomia. By observing changes in Dysnomia's orbit projected on the sky over multiple different epochs, we were able to break the mirror degeneracy and determine the pole orientation of Eris. Images of the Eris/Dysnomia system were obtained with WFC3/HST in January and February 2018 (program 15171). These images were taken through the F606W filter and visits were scheduled to capture Dysnomia at different orbital phases. We also folded in data from ACS/HRC/HST and NIRC2/Keck programs from 2005/2006 (Brown and Schaller, 2007) and WFC3/HST program 13668 from 2015. The 2005/2006 data were considered "Epoch 1" and the 2015 and 2018 data were combined into "Epoch 2." PSF-fitting produced relative astrometry of Dysnomia with respect to Eris and was used to fit Keplerian orbits to each epoch. Comparison of the orbit fits from these different epochs enabled the determination of Eris' rotation pole orientation, assuming Dysnomia orbits in Eris' equatorial plane. We report that Eris' obliquity is 78, the sub-solar latitude in early 2018 was 42, and the next period of mutual events will occur in 2239, all in agreement with Orbit 1 from Brown and Schaller (2007). With this viewing geometry, approximately 30% of the visible hemisphere of Eris is in constant sunlight. Assuming a peak-to-valley amplitude of 0.10 mag (Roe et al., 2008) due entirely to albedo variations, the hemispheres representing the maximum and minimum in the light curve have a 10% difference in albedo. Eris' high visible geometric albedo (0.96; Sicardy et al., 2011) and this small albedo difference together imply that Eris' surface lacks large-scale, low-albedo features like Cthulhu Macula on Pluto.
  66. Olkin, C., Moore, J., Stern, A., et al., (including Grundy, W.), 2018, DPS, 50, 509.05, Great Expectations: Anticipating Results from the First Encounter with a Cold Classical Kuiper Belt Object
    On January 1, 2019, the New Horizons spacecraft will encounter 2014 MU69 (nicknamed Ultima Thule). Little is known about this object, but its orbit and color are consistent with the cold classical population. The flyby of New Horizons past 2014 MU69 will be the first close-up look at a cold classical Kuiper Belt object - a primordial object. Given theories of the dynamic and chaotic nature of solar system evolution, the cold classical population of the Kuiper belt has emerged as a singular candidate for a fundamentally unaltered original planetesimal population. This flyby of 2014 MU69 is a unique opportunity to explore the disk processes and chemistry of the primordial solar nebula. As such, compositional measurements during the NH flyby are of paramount importance. So is high-resolution imaging of shape and structure, as the intermediate size of MU69 (much smaller than Pluto but much larger than a typical comet) may show signs of its accretion from much smaller bodies (layers, pebbles, lobes, etc., in the manner of 67P/C-G), or alternatively, derivation via the collisional fragmentation of a larger body if KBOs are "born big". MU69 may also be big enough to show signs of internal evolution driven by radiogenic heat from 26Al decay, if it accreted early enough and fast enough. The size of MU69 (20 - 40 km) places it in a class that has the potential to harbor unusual, and in some cases, possibly active, surface geological processes: several small satellites of similar size, including Helene and Epimetheus, display what appears to be fine-grained material covering large portions of their surfaces, and the surface of Phobos displays an unusual system of parallel grooves. Invariably, these intriguing surface features are only clearly defined at imaging resolutions of at least tens of meters per pixel. The best images of MU69 are planned to have resolutions of 20 - 40 m/pixel at a phase angle range of 40 - 70. We also plan color imaging at 200 - 500 m/pixel, and spectroscopy from 1.25 to 2.5 m at 1 - 4 km/pixel. Additionally, we will search for satellites and rings around 2014 MU69, make disk averaged measurements of the object's brightness temperature, and search for coma using the Alice UV spectrometer.
  67. Clarke, C., Tazzari, M., Juhasz, A., et al., (including Prato, L.), 2018, ApJL, 866, L6, High-resolution Millimeter Imaging of the CI Tau Protoplanetary Disk: A Massive Ensemble of Protoplanets from 0.1 to 100 au
    We present high-resolution millimeter continuum imaging of the disk surrounding the young star CI Tau, a system hosting the first hot Jupiter candidate in a protoplanetary disk system. The system has extended mm emission on which are superposed three prominent annular gaps at radii 13, 39, and 100 au. We argue that these gaps are most likely to be generated by massive planets so that, including the hot Jupiter, the system contains four gas giant planets at an age of only 2 Myr. Two of the new planets are similarly located to those inferred in the famous HL Tau protoplanetary disk; in CI Tau, additional observational data enables a more complete analysis of the system properties than was possible for HL Tau. Our dust and gas dynamical modeling satisfies every available observational constraint and points to the most massive ensemble of exoplanets ever detected at this age, with its four planets spanning a factor 1000 in orbital radius. Our results show that the association between hot Jupiters and gas giants on wider orbits, observed in older stars, is apparently in place at an early evolutionary stage.
  68. Hora, J., Siraj, A., Mommert, M., et al., 2018, ApJS, 238, 22, Infrared Light Curves of Near-Earth Objects
    We present light curves and derive periods and amplitudes for a subset of 38 near-Earth objects (NEOs) observed at 4.5 m with the IRAC camera on the the Spitzer Space Telescope, many of them having no previously reported rotation periods. This subset was chosen from about 1800 IRAC NEO observations as having obvious periodicity and significant amplitude. For objects where the period observed did not sample the full rotational period, we derived lower limits to these parameters based on sinusoidal fits. Light curve durations ranged from 42 to 544 minutes, with derived periods from 16 to 270 minutes. We discuss the effects of light curve variations on the thermal modeling used to derive diameters and albedos from Spitzer photometry. We find that both diameters and albedos derived from the light curve maxima and minima agree with our previously published results, even for extreme objects, showing the conservative nature of the thermal model uncertainties. We also evaluate the NEO rotation rates, sizes, and their cohesive strengths.
  69. Bair, A., Schleicher, D., Knight, M., 2018, AJ, 156, 159, Coma Morphology, Numerical Modeling, and Production Rates for Comet C/Lulin (2007 N3)
    We report on narrowband photometry and extensive imaging observations of comet C/Lulin (2007 N3) obtained at Lowell Observatory during 2008 and 2009. Enhanced CN images revealed a double-corkscrew morphology with two near-polar jets oriented approximately east-west, and both CN and dust images showed nightly rotational variability and seasonal changes in bulk morphology. We determined a rotational pole direction of R.A./decl. = 81/+29 with an obliquity of 97 and a sidereal rotation period of 41.45 0.05 hr. Monte Carlo numerical modeling best replicated the observed CN features with an eastern source area at lat/long -80/125 and an 10 radius and a western source area at lat/long +77/245 and an 20 radius, 4 larger than the eastern source. An additional small, near-equatorial source was necessary to reproduce some dust features. Water morphology based on OH was quite different from that of the carbon-bearing species, implying a different driver for the polar jets such as CO or CO2. Ion tails were detected in decontaminated images from both the dust and NH filters, likely being H2O+ and OH+, respectively. We measured water production both before and after perihelion and extrapolated peak water production at perihelion to be about 1.0 1029 molecules s-1. We estimated an active fraction of only 4%-5% and a nucleus radius of up to 8 km. Our data suggest that Lulin, defined as dynamically new in a statistical sense, behaves more like a long-period comet due to its nearly asteroidal early appearance, isolated source regions, and dust properties.
  70. Borisov, G., Devogele, M., Cellino, A., et al., 2018, MNRAS, 480, L131, Rotational variation of the linear polarization of the asteroid (3200) Phaethon as evidence for inhomogeneity in its surface properties
    Asteroid (3200) Phaethon is a Near-Earth Apollo asteroid with an unusual orbit that brings it closer to the Sun than any other known asteroid. Its last close approach to the Earth was in 2017 mid-December and the next one will be on 2026 October. Previous rotationally time-resolved spectroscopy of Phaethon showed that its spectral slope is slightly bluish, in agreement with its B/F taxonomic classification, but at some rotational phases, it changes to slightly reddish. Motivated by this result, we performed time-resolved imaging polarimetry of Phaethon during its recent close approach to the Earth. Phaethon has a spin period of 3.604 h, and we found a variation of the linear polarization with rotation. This seems to be a rare case in which such variation is unambiguously found, also a consequence of its fairly large amplitude. Combining this new information with the brightness and colour variation as well as previously reported results from Arecibo radar observations, we conclude that there is no variation of the mineralogy across the surface of Phaeton. However, the observed change in the linear polarization may be related to differences in the thickness of the surface regolith in different areas or local topographic features.
  71. Cellino, A., Devogele, M., Belskaya, I., et al., 2018, EPSC, EPSC2018-251, (3200) Phaethon: asteroid or comet?
    Our polarimetric measurements of (3200) Phaethon indicate that this object is most probably an asteroid, rather than a comet, in spite of having unusual orbital properties and being the parent body of the Geminid shower. We confirm previous suggestions that it could likely be a fugitive from the dynamical family of (2) Pallas. We find that Phaethon exhibits the highest values of linear polarization ever found for small solar system objects. Its polarimetric properties also suggest a low-albedo, as opposite to higher albedos resulting from thermal IR data.
  72. Gabasova, L., Blanchard, N., Schmitt, B., et al., (including Grundy, W.), 2018, EPSC, EPSC2018-537, Progressive metaheuristics for high-dimensional radiative transfer model inversion
    Determining planetary surface composition via remote spectroscopy frequently requires the use of inverse modeling, as the surface presents a complex mixture of materials which cannot be directly identified from the spectra. Depending on the complexity of the radiative transfer model (RTM) used, however, the inverse problem can be nonlinear and very high-dimensional, and the computational cost of traditional optimization methods becomes prohibitive. We demonstrate the utility of a multi-step metaheuristic approach for the inversion of high-dimensional RTMs, using the example of Pluto.
  73. Devogele, M., Moskovitz, N., Thomas, C., et al., 2018, EPSC, EPSC2018-572, The Mission Accessible Near-Earth Objects Survey (MANOS): first results from the visible spectroscopic survey
    The Mission Accessible Near-Earth Objects Survey (MANOS) aims at characterizing sub-km, low delta- v, newly discovered Near-Earth Objects (NEOs). This survey, started in August 2013, is collecting astrometry, lightcurve photometry, and reflectance spectra of this under-studied portion of the NEO population. The MANOS program is using 1 to 8 meter tele- scopes located around the world. Here we present the first results of the visible reflectance spectroscopy survey obtained with the 8.1-meter Gemini North and South telescopes, the 4.3-meter Discovery Channel Telescope and the 4.1-meter SOAR telescope.
  74. Hromakina, T., Belskaya, I., Krugly, Y., et al., (including Thirouin, A.), 2018, EPSC, EPSC2018-692, An extensive photometric study of the dwarf planet Makemake
    We will present a photometric study of the dwarf planet Makemake based on new observational data obtained between 2006 and 2017 using 0.7 to 3.6-m telescopes around the world. Based on this extensive dataset we derive a high precision rotational period estimate. The resulting lightcurve has a small peak-to-peak amplitude variability, that implies an almost spherical shape or an elongated object in a pole-on orientation. Multi-colour observations allowed us to measure surface colours of Makemake. The magnitude phase dependence slope is quite low and is similar to other bodies with methane ice-rich surfaces. Combining our and literature data we tested Makemake for the existence of long-term brightness variations, and searched for the signs of a satellite.
  75. Oszkiewicz, D., Kryszczynska, A., Kankiewicz, P., et al., (including Moskovitz, N., Skiff, B.), 2018, EPSC, EPSC2018-846, The unusual V-type asteroid (2579) Spartacus
    Asteroid (2579) Spartacus is a small V-type object located in the inner main belt (the main delivery region for meteorites). It shows spectral characteristics different from typical values for Vestoids, which may indicate origin deeper within Vesta then other V-types or a different parent body. We determine physical and dynamical properties of (2579) Spartacus and discuss its possible origin scenarios.
  76. Schmidt, C., Baumgardner, J., Moore, L., et al., (including Bida, T.), 2018, EPSC, EPSC2018-1216, Ground-Based BepiColombo Support with the Rapid Imaging Planetary Spectrograph
    A new instrument has been developed for observing Mercury's atmosphere to support the BepiColombo mission. The technique employed is entirely new, and uses very fast imaging to offer new insights about the atmosphere's coupling to the magnetosphere and solar wind.
  77. Stern, S., Grundy, W., McKinnon, W., et al., 2018, ARA&A, 56, 357, The Pluto System After New Horizons
    The New Horizons (NH) flyby of the Pluto-Charon binary planet and its system of four small surrounding satellites in mid-2015 revolutionized our knowledge of this distant planet and its moons. Beyond providing rich geo-logical, compositional, and atmospheric data sets, NH demonstrated that Pluto has been surprisingly geologically and climatologically active throughout the past 4+ Gyr and that the planet exhibits a remarkably complex range of atmospheric phenomenology and geological expressions that rival Mars in their richness. In contrast, Pluto's large, planet-sized satellite Charon, though also geologically complex, has no detected active surface volatiles, has no detectable atmosphere, has much more muted colors, has lower albedo, and exhibits only ancient terrains. Pluto's system of four small satellites orbiting outside of Charon is itself dynamically complex and geologically interesting. Here, we review both what was known about the Pluto system before NH and what it has taught us about the Pluto system specifically and, by inference, other small planets in the Kuiper Belt. We go on to examine the natural next steps in Kuiper Belt exploration.
  78. Mommert, M., McNeill, A., Trilling, D., et al., (including Moskovitz, N.), 2018, AJ, 156, 139, The Main Belt Asteroid Shape Distribution from Gaia Data Release 2
    Gaia Data Release 2 includes observational data for 14099 pre-selected asteroids. From the sparsely sampled G-band photometry, we derive lower-limit light curve amplitudes for 11665 main belt asteroids (MBA) in order to provide constraints on the distribution of shapes in the asteroid main belt. Assuming a triaxial shape model for each asteroid, defined through the axial aspect ratios a > b and b = c, we find an average b/a = 0.80 0.04 for the ensemble, which is in agreement with previous results. By combining the Gaia data with asteroid properties from the literature, we investigate possible correlations of the aspect ratio with size, semimajor axis, geometric albedo, and intrinsic color. Based on our model simulations, we find that MBAs greater than 50 km in diameter on average have higher b/a aspect ratios (are rounder) than smaller asteroids. We furthermore find significant differences in the shape distribution of MBAs as a function of the other properties that do not affect the average aspect ratios. We conclude that a more detailed investigation of shape distribution correlations requires a larger data sample than is provided in Gaia Data Release 2.
  79. Devogele, M., Cellino, A., Borisov, G., et al., 2018, MNRAS, 479, 3498, The phase-polarization curve of asteroid (3200) Phaethon
    A multicolour phase-polarization curve of asteroid (3200) Phaethon has been obtained during the 2017 December apparition by merging measurements taken at the observing station of Calern (France) and at the Rozhen observatory (Bulgaria). All the observations were obtained in the positive polarization branch, the phase angle ranging from 36 to 116. The measured values of linear polarization are among the highest ever observed for a Solar system body. The covered interval of phase angle was not sufficiently extended to derive a firm determination of the Pmax parameter, but this appears to occur at a phase angle around 130 and reaches more than 45 per cent of linear polarization. Phaethon is the parent body of the Geminid meteor shower, and the real physical nature of this object (asteroid or comet) has been a long-debated subject. Our polarimetric measurements seem to support the asteroid hypothesis with a phase-polarization curve similar to the asteroid (2) Pallas, but further observations at smaller phase angles are needed to draw definitive conclusions.
  80. Moore, J., McKinnon, W., Cruikshank, D., et al., (including Grundy, W.), 2018, GeoRL, 45, 8111, Great Expectations: Plans and Predictions for New Horizons Encounter With Kuiper Belt Object 2014 MU69 ("Ultima Thule")
    The New Horizons encounter with the cold classical Kuiper Belt object 2014 MU69 (informally named "Ultima Thule," hereafter Ultima) on 1 January 2019 will be the first time a spacecraft has ever closely observed one of the free-orbiting small denizens of the Kuiper Belt. Related to but not thought to have formed in the same region of the solar system as the comets that been explored so far, it will also be the most distant, and most primitive body yet visited by spacecraft. In this letter we begin with a brief overview of cold classical Kuiper Belt objects, of which Ultima is a prime example. We give a short preview of our encounter plans. We note what is currently known about Ultima from Earth-based observations. We then review our expectations and capabilities to evaluate Ultima's composition, surface geology, structure, near space environment, small moons, rings, and the search for activity.
  81. Sheppard, S., Williams, G., Tholen, D., et al., (including Thirouin, A., Devogele, M., Moskovitz, N.), 2018, RNAAS, 2, 155, New Jupiter Satellites and Moon-Moon Collisions
    We report the discovery of 12 new satellites of Jupiter, giving Jupiter 79 known satellites. The new finds are between 23rd-24th mag in the r-band and 1-3 km in diameter assuming dark albedos. Nine of the discoveries are in the distant retrograde satellite groupings. Two of the new satellites are in the closer Himalia prograde group near 28 degrees in inclination. S/2016 J2, nicknamed Valetudo, has an orbit unlike any other known outer satellite and is the most distant prograde satellite around any planet at 0.36 Hill radii. Numerical simulations show S/2016 J2 is very stable, with average and range of i=34.2+-3 deg, e=0.216+-0.125, and a=18.9+-0.7 million km over 100 Myrs. Our stability simulations show a S/2016 J2 like orbit would be stable out to a=21.8 million km or 0.41 Hill radii, but no further, unlike more distant and eccentric retrograde satellites. S/2016 J2's large semi-major axis means it significantly overlaps the orbits of the distant retrogrades. A prograde-retrograde moon-moon collision between outer satellites of Jupiter has likely happened over the age of the solar system.
  82. Neugent, K., Massey, P., Morrell, N., 2018, ApJ, 863, 181, A Modern Search for Wolf-Rayet Stars in the Magellanic Clouds. IV. A Final Census
    We summarize the results of our 4 yr survey searching for Wolf-Rayet (WR) stars in the Large Magellanic Cloud (LMC) and Small Magellanic Cloud. Over the course of this survey we have discovered 15 new WR stars and 12 Of-type stars. In this last year we discovered two rare Of-type stars: an O6.5f?p and an O6nfp, in addition to the two new Of?p stars discovered in our first year and the three Onfp stars discovered in our second and third years. However, even more exciting was our discovery of a new type of WR star, ones we are calling WN3/O3s owing to their spectroscopic signatures. We describe the completeness limits of our survey and demonstrate that we are sensitive to weak-lined WRs several magnitudes fainter than any we have discovered, arguing that there is not a population of fainter WRs waiting to be discovered. We discuss the nature of the WN3/O3s, summarizing the results of our extensive spectroscopy and modeling. We also examine the important claim made by others that the WN3/O3s are isolated compared to other massive stars. We find that if we use a more complete sample of reference massive stars, the WN3/O3s show the same spatial distribution as other early WNs, consistent with a common origin. Finally, we use this opportunity to present the Fifth Catalog of LMC Wolf-Rayet Stars, which includes revised coordinates and updated spectral types for all 154 known LMC WRs.

    This paper includes data gathered with the 1 m Swope and 6.5 m Magellan telescopes located at Las Campanas Observatory, Chile.

  83. Davis, B., Ciardullo, R., Jacoby, G., et al., 2018, ApJ, 863, 189, The True Luminosities of Planetary Nebulae in M31's Bulge: Massive Central Stars from an Old Stellar Population
    We measure the Balmer decrements of 23 of the brightest planetary nebulae (PNe) in the inner bulge (r 3) of M31 and deredden the bright end of the regions [O III] 5007 PN luminosity function. We show that the most luminous PNe produce 1200 L of power in their [O III] 5007 line, implying central star luminosities of at least 11,000 L . Even with the most recent accelerated-evolution post-AGB models, such luminosities require central star masses in excess of 0.66 M and main-sequence progenitors of at least 2.5 M . Since M31's bulge has very few intermediate-age stars, we conclude that conventional single-star evolution cannot be responsible for these extremely luminous objects. We also present the circumstellar extinctions for the regions bright PNe and demonstrate that the distribution is similar to that found for PNe in the Large Magellanic Cloud, with a median value of A 5007 = 0.71. Finally, we compare our results to extinction measurements made for PNe in the E6 elliptical NGC 4697 and the interacting lenticular NGC 5128. We show that such extinctions are not unusual and that the existence of very high-mass PN central stars is a general feature of old stellar populations. Our results suggest that single-star population synthesis models significantly underestimate the maximum luminosities and total integrated light of AGB stars.
  84. Agarwal, J., Mommert, M., 2018, A&A, 616, A54, Nucleus of active asteroid 358P/Pan-STARRS (P/2012 T1)
    Context. The dust emission from active asteroids is likely driven by collisions, fast rotation, sublimation of embedded ice, and combinations of these. Characterising these processes leads to a better understanding of their respective influence on the evolution of the asteroid population.
    Aims: We study the role of fast rotation in the active asteroid 358P (P 2012/T1).
    Methods: We obtained two nights of deep imaging of 358P with SOAR/Goodman and VLT/FORS2. We derived the rotational light curve from time-resolved photometry and searched for large fragments and debris >8 mm in a stacked, ultra-deep image.
    Results: The nucleus has an absolute magnitude of mR = 19.68, corresponding to a diameter of 530 m for standard assumptions on the albedo and phase function of a C-type asteroid. We do not detect fragments or debris that would require fast rotation to reduce surface gravity to facilitate their escape. The 10-h light curve does not show an unambiguous periodicity.
  85. Kammer, J., Becker, T., Retherford, K., et al., (including Wasserman, L.), 2018, AJ, 156, 72, Probing the Hill Sphere of (486958) 2014 MU69: HST FGS Observations during the 2017 July 17 Stellar Occultation
    We observed the 2017 July 17 stellar occultation of HD 168233 by the Kuiper Belt Object (486958) 2014 MU69, the close flyby target of the extended New Horizons mission. Rather than capture a solid body occultation by the KBO itself, our program aimed to constrain the opacity of rings, moons, or other debris in the nearby environment. We used the Hubble Space Telescope Fine Guidance Sensors (HST FGS) instrument in TRANS F583W mode to collect 40 Hz time resolution photometry of the stellar occultation star for two HST orbits during this observation. We present the results of reduction and calibration of the HST FGS photometry, and set upper limits on rings or other dust opacity within the Hill sphere of (486958) 2014 MU69 at distances ranging from 20000 km to 75000 km from the main body.
  86. Flagg, L., Johns-Krull, C., Prato, L., et al., (including Nofi, L., Llama, J., Sullivan, K.), 2018, csss, 41, A Search for the Direct Detection of the 2 Myr Old Hot Jupiter Orbiting CI Tau
    Characterizing young exoplanets is critical for putting limits on planet formation scenarios. However, as of yet, only a few young exoplanet candidates have even been discovered, and no young planet with a model-independent mass has had its spectrum or brightness measured. A good candidate for such a detection is CI Tau b, an msini = 8.1 Mjup planet in a 9 day orbit around a 2 Myr old classical T Tauri star. We use high spectral resolution K band echelle spectroscopy to look for direct signatures of the planet itself, taking advantage of the large expected radial velocity variations of the planet as it orbits CI Tau. We report on our efforts to directly detect the spectrum of CI Tau b and present a tentative measurement of CO absorption in this young exoplanet. The properties of the planet determined from this CO detection are consistent with those described in the discovery paper and favor "hot start" formation models.
  87. Bertrand, T., Forget, F., Umurhan, O., et al., (including Grundy, W.), 2018, Icar, 309, 277, The nitrogen cycles on Pluto over seasonal and astronomical timescales
    Pluto's landscape is shaped by the endless condensation and sublimation cycles of the volatile ices covering its surface. In particular, the Sputnik Planitia ice sheet, which is thought to be the main reservoir of nitrogen ice, displays a large diversity of terrains, with bright and dark plains, small pits and troughs, topographic depressions and evidences of recent and past glacial flows. Outside Sputnik Planitia, New Horizons also revealed numerous nitrogen ice deposits, in the eastern side of Tombaugh Regio and at mid-northern latitudes.

    These observations suggest a complex history involving volatile and glacial processes occurring on different timescales. We present numerical simulations of volatile transport on Pluto performed with a model designed to simulate the nitrogen cycle over millions of years, taking into account the changes of obliquity, solar longitude of perihelion and eccentricity as experienced by Pluto. Using this model, we first explore how the volatile and glacial activity of nitrogen within Sputnik Planitia has been impacted by the diurnal, seasonal and astronomical cycles of Pluto. Results show that the obliquity dominates the N2 cycle and that over one obliquity cycle, the latitudes of Sputnik Planitia between 25S-30N are dominated by N2 condensation, while the northern regions between 30N and -50N are dominated by N2 sublimation. We find that a net amount of 1 km of ice has sublimed at the northern edge of Sputnik Planitia during the last 2 millions of years. It must have been compensated by a viscous flow of the thick ice sheet. By comparing these results with the observed geology of Sputnik Planitia, we can relate the formation of the small pits and the brightness of the ice at the center of Sputnik Planitia to the sublimation and condensation of ice occurring at the annual timescale, while the glacial flows at its eastern edge and the erosion of the water ice mountains all around the ice sheet are instead related to the astronomical timescale. We also perform simulations including a glacial flow scheme which shows that the Sputnik Planitia ice sheet is currently at its minimum extent at the northern and southern edges. We also explore the stability of N2 ice deposits outside the latitudes and longitudes of the Sputnik Planitia basin. Results show that N2 ice is not stable at the poles but rather in the equatorial regions, in particular in depressions, where thick deposits may persist over tens of millions of years, before being trapped in Sputnik Planitia. Finally, another key result is that the minimum and maximum surface pressures obtained over the simulated millions of years remain in the range of milli-Pascals and Pascals, respectively. This suggests that Pluto never encountered conditions allowing liquid nitrogen to flow directly on its surface. Instead, we suggest that the numerous geomorphological evidences of past liquid flow observed on Pluto's surface are the result of liquid nitrogen that flowed at the base of thick ancient nitrogen glaciers, which have since disappeared.

  88. van Belle, G., Armstrong, J., Benson, J., et al., (including DeGroff, W., Hall, J., Lindgren, A., Pooler, S.), 2018, SPIE, 10701, 1070105, Many interesting things are afoot at the Navy Precision Optical Interferometer
    The Navy Precision Optical Interferometer (NPOI) is currently undergoing a fundamental renaissance in its functionality and capabilities. Operationally, its fast delay line (FDL) infrastructure is completing its upgrade from a VME/VxWorks foundation to a modern PC/RTLinux core. The Classic beam combiner is being upgraded with the New Classic FPGA-based backend, and the VISION beam combiner has been upgraded over this past summer with low-noise EMCCD cameras, resulting in substantial gains in sensitivity. Building on those infrastructure improvements, substantial upgrades are also in progress. Three 1-meter PlaneWave CDK1000 telescopes are being delivered to the site, along with their relocatable enclosure-transporters, and stations are being commissioned for those telescopes with baselines ranging from 8 meters to 432 meters. Baseline-wavelength bootstrapping will be implemented on the facility back-end with a near-infrared beam combiner under development. Collectively, these improvements mark substantial progress in taking the facility towards realizing its full intrinsic potential.
  89. Armstrong, J., Schmitt, H., Restaino, S., et al., (including van Belle, G.), 2018, SPIE, 10701, 107010B, An infrared beam combiner for wavelength bootstrapping at the NPOI
    Since 1994, the Navy Precision Optical Interferometer (NPOI) has operated at visual wavelengths (450 to 850 nm). Its primary Classic backend is a pupil-plane combiner that disperses the light at a resolution R 50, uses avalanche photo-diodes as photon-counting detectors, and scans interference fringes by modulating the delay at 1 kHz. The newer NPOI image-plane combiner, VISION (Tennessee State University), which is similar to CHARA's MIRC and is currently being upgraded, dispenses with delay modulation. We are now developing a third backend to expand into the near infrared. Its primary purpose will be to stabilize the NPOI for high-resolution observations by bootstrapping from the infrared to visual wavelengths.
  90. Monnier, J., Ireland, M., Kraus, S., et al., (including van Belle, G.), 2018, SPIE, 10701, 1070118, Planet formation imager: project update
    The Planet Formation Imager (PFI) is a near- and mid-infrared interferometer project with the driving science goal of imaging directly the key stages of planet formation, including the young proto-planets themselves. Here, we will present an update on the work of the Science Working Group (SWG), including new simulations of dust structures during the assembly phase of planet formation and quantitative detection efficiencies for accreting and non-accreting young exoplanets as a function of mass and age. We use these results to motivate two reference PFI designs consisting of a) twelve 3m telescopes with a maximum baseline of 1.2km focused on young exoplanet imaging and b) twelve 8m telescopes optimized for a wider range of young exoplanets and protoplanetary disk imaging out to the 150K H2O ice line. Armed with 4 x 8m telescopes, the ESO/VLTI can already detect young exoplanets in principle and projects such as MATISSE, Hi-5 and Heimdallr are important PFI pathfinders to make this possible. We also discuss the state of technology development needed to make PFI more affordable, including progress towards new designs for inexpensive, small field-of-view, large aperture telescopes and prospects for Cubesat-based space interferometry.
  91. Hahne, F., Horch, E., van Belle, G., et al., (including Clark, C.), 2018, SPIE, 10701, 107012A, Two-color speckle imaging of M-dwarfs with the Discovery Channel telescope
    Lowell Observatory and Southern Connecticut State University are currently involved in a joint project to determine the stellar multiplicity rates and the fundamental stellar parameters of M dwarf stars using the Differential Speckle Survey Instrument (DSSI) at Lowell's Discovery Channel Telescope (DCT). DSSI observes speckle patterns simultaneously at two separate wavelengths, allowing color measurements of the components of a binary system to be made in a single observation. This paper will describe the initial data gathering process, which began in 2016. Since then, over 1000 stars have been observed. We summarize the analysis on these objects so far, and discuss the relevance of these observations for existing and future space missions such as TESS, JWST, and Gaia.
  92. Mace, G., Sokal, K., Lee, J., et al., (including Prato, L., Jacoby, G., Cornelius, F., Hardesty, B., DeGroff, W., Dunham, E., Levine, S., Nofi, L.), 2018, SPIE, 10702, 107020Q, IGRINS at the Discovery Channel Telescope and Gemini South
    The Immersion GRating INfrared Spectrometer (IGRINS) was designed for high-throughput with the expectation of being a visitor instrument at progressively larger observing facilities. IGRINS achieves R45000 and > 20,000 resolution elements spanning the H and K bands (1.45-2.5m) by employing a silicon immersion grating as the primary disperser and volume-phase holographic gratings as cross-dispersers. After commissioning on the 2.7 meter Harlan J. Smith Telescope at McDonald Observatory, the instrument had more than 350 scheduled nights in the first two years. With a fixed format echellogram and no cryogenic mechanisms, spectra produced by IGRINS at different facilities have nearly identical formats. The first host facility for IGRINS was Lowell Observatory's 4.3-meter Discovery Channel Telescope (DCT). For the DCT a three-element fore-optic assembly was designed to be mounted in front of the cryostat window and convert the f/6.1 telescope beam to the f/8.8 beam required by the default IGRINS input optics. The larger collecting area and more reliable pointing and tracking of the DCT improved the faint limit of IGRINS, relative to the McDonald 2.7-meter, by 1 magnitude. The Gemini South 8.1-meter telescope was the second facility for IGRINS to visit. The focal ratio for Gemini is f/16, which required a swap of the four-element input optics assembly inside the IGRINS cryostat. At Gemini, observers have access to many southern-sky targets and an additional gain of 1.5 magnitudes compared to IGRINS at the DCT. Additional adjustments to IGRINS include instrument mounts for each facility, a glycol cooled electronics rack, and software modifications. Here we present instrument modifications, report on the success and challenges of being a visitor instrument, and highlight the science output of the instrument after four years and 699 nights on sky. The successful design and adaptation of IGRINS for various facilities make it a reliable forerunner for GMTNIRS, which we now anticipate commissioning on one of the 6.5 meter Magellan telescopes prior to the completion of the Giant Magellan Telescope.
  93. Dunham, E., Bida, T., Chylek, T., et al., (including Cornelius, F., Moskovitz, N.), 2018, SPIE, 10702, 107023E, NIHTS: the near-infrared high throughput spectrograph for the Discovery Channel Telescope
    NIHTS is a first-generation instrument now in use on Lowell Observatory's Discovery Channel Telescope. It is a nearinfrared prism spectrograph of the BASS design featuring high throughput and low dispersion that is intended for observations of faint solar system and astrophysical objects over the YJHK spectral range. An unusual feature is its ability to observe simultaneously with the Large Monolithic Imager, an optical CCD camera, by means of a dichroic fold mirror. This is particularly valuable for time-variable targets such as Kuiper Belt Objects, asteroids, exoplanet transits, and brown dwarfs. We describe its design details and performance both in the lab and on the telescope.
  94. Scowen, P., Shkolnik, E., Ardila, D., et al., (including Llama, J.), 2018, SPIE, 10699, 106990F, Monitoring the high-energy radiation environment of exoplanets around low-mass stars with SPARCS (Star-Planet Activity Research CubeSat)
    Roughly 40 billion M dwarfs in our galaxy host at least one small planet in the habitable zone (HZ). The stellar ultraviolet (UV) radiation from M dwarfs is strong and highly variable, and impacts planetary atmospheric loss, composition and habitability. These effects are amplified by the extreme proximity of their HZs (0.1-0.4 AU). Knowing the UV environments of M dwarf planets will be crucial to understanding their atmospheric composition and a key parameter in discriminating between biological and abiotic sources for observed biosignatures. The Star-Planet Activity Research CubeSat (SPARCS) will be a 6U CubeSat devoted to photometric monitoring of M stars in the far-UV and near-UV, measuring the time-dependent spectral slope, intensity and evolution of low-mass star high-energy radiation.
  95. Levine, S., DeGroff, W., Bida, T., et al., (including Dunham, E., Jacoby, G.), 2018, SPIE, 10700, 107004P, Status and performance of Lowell Observatory's Discovery Channel telescope and its growing suite of instruments
    Lowell Observatory's Discovery Channel Telescope (DCT) is a 4.3-m telescope designed and constructed for optical and near infrared astronomical observation. The DCT is equipped with a cube at the RC focus capable of interfacing to five instruments along with the wave front sensing and guider systems at the f/6.1 RC focus. Over the period 2016 through mid-2018 the instrument cube ports were fully populated as several instruments new to the DCT were brought on-line (NIHTS, IGRINS, EXPRES). The primary and secondary mirrors of the telescope were re-aluminized, and the coating process modified. The facility operational modes have been refined to allow for greater flexibility and faster response to unexpected science opportunities. This report addresses operational methods, instrumentation integration, and the performance of the facility as determined from delivered science data, lessons learned, and plans for future work and additional instruments.
  96. Erasmus, N., McNeill, A., Mommert, M., et al., 2018, ApJS, 237, 19, Taxonomy and Light-curve Data of 1000 Serendipitously Observed Main-belt Asteroids
    We present VRI spectrophotometry of 1003 main-belt asteroids (MBAs) observed with the Sutherland, South Africa node of the Korea Microlensing Telescope Network (KMTNet). All of the observed MBAs were serendipitously captured in KMTNets large 2 2 field of view during a separate targeted near-Earth Asteroid study. Our broadband spectrophotometry is reliable enough to distinguish among four asteroid taxonomies and we confidently categorize 836 of the 1003 observed targets as either a S-, C-, X-, or D-type asteroid by means of a machine learning algorithm approach. Our data show that the ratio between S-type MBAs and (C+X+D)-type MBAs, with H magnitudes between 12 and 18 (12 km diameter 0.75 km), is almost exactly 1:1. Additionally, we report 0.5-3 hr (median: 1.3 hr) light-curve data for each MBA and we resolve the complete rotation periods and amplitudes for 59 targets. Of the 59 targets, 2 have rotation periods potentially below the theoretical zero-cohesion boundary limit of 2.2 hr. We report lower limits for the rotation periods and amplitudes for the remaining targets. Using the resolved and unresolved light curves we determine the shape distribution for this population using a Monte Carlo simulation. Our model suggests a population with an average elongation b/a = 0.74 0.07 and also shows that this is independent of asteroid size and taxonomy.
  97. Hsieh, H., Ishiguro, M., Knight, M., et al., (including Moskovitz, N.), 2018, AJ, 156, 39, The Reactivation and Nucleus Characterization of Main-belt Comet 358P/PANSTARRS (P/2012 T1)
    We present observations of main-belt comet (MBC) 358P/PANSTARRS (P/2012 T1) obtained using the Gemini South telescope from 2017 July to December, as the object approached perihelion for the first time since its discovery. We find best-fit IAU phase function parameters of H R = 19.5 0.2 mag and G R = -0.22 0.13 for the nucleus, corresponding to an effective radius of r N = 0.32 0.03 km (assuming an albedo of p R = 0.05). The object appears significantly brighter (by 1 mag) than expected starting in 2017 November, while a faint dust tail oriented approximately in the antisolar direction is also observed on 2017 December 18. We conclude that 358P has become active again for the first time since its previously observed active period in 2012-2013. These observations make 358P the seventh MBC candidate confirmed to exhibit recurrent activity near perihelion with intervening inactivity away from perihelion, strongly indicating that its activity is sublimation-driven. Fitting a linear function to the ejected dust masses inferred for 358P in 2017 when it is apparently active, we find an average net dust production rate of \dot{M}=2.0+/- 0.6 kg s-1 (assuming a mean effective particle radius of {\bar{a}}d=1 mm) and an estimated activity start date of 2017 November 8 4 when the object was at a true anomaly of = 316 1 and a heliocentric distance of R = 2.54 au. Insufficient data is currently available to ascertain whether activity strength has changed between the objects 2012-2013 and 2017 active periods. Further observations are therefore highly encouraged during the objects upcoming observing window (2018 August through 2019 May).
  98. Hunter, D., Adamo, A., Elmegreen, B., et al., (including Gallardo, S.), 2018, AJ, 156, 21, A Comparison of Young Star Properties with Local Galactic Environment for LEGUS/LITTLE THINGS Dwarf Irregular Galaxies
    We have explored the role environmental factors play in determining characteristics of young stellar objects in nearby dwarf irregular and blue compact dwarf galaxies. Star clusters are characterized by concentrations, masses, and formation rates; OB associations by mass and mass surface density; O stars by their numbers and near-ultraviolet absolute magnitudes; and H II regions by H surface brightnesses. These characteristics are compared to surrounding galactic pressure, stellar mass density, H I surface density, and star formation rate (SFR) surface density. We find no trend of cluster characteristics with environmental properties, implying that larger-scale effects are more important in determining cluster characteristics or that rapid dynamical evolution erases any memory of the initial conditions. On the other hand, the most massive OB associations are found at higher pressure and H I surface density, and there is a trend of higher H II region H surface brightness with higher pressure, suggesting that a higher concentration of massive stars and gas is found preferentially in regions of higher pressure. At low pressures we find massive stars but not bound clusters and OB associations. We do not find evidence for an increase of cluster formation efficiency as a function of SFR density. However, there is an increase in the ratio of the number of clusters to the number of O stars with increasing pressure, perhaps reflecting an increase in clustering properties with SFR.
  99. Cushing, M., Moskovitz, N., Gustafsson, A., 2018, RNAAS, 2, 50, Spectroscopic Confirmation That 2MASS J07414279-0506464 Is a Mid-type L Dwarf
    We present a low-resolution near-infrared spectrum of 2MASS J07414279-0506464, a mid-type L dwarf candidate recently identified by Scholz & Bell. The spectrum was obtained using the Near-Infrared High Throughput Spectrograph (NIHTS) on Lowell Observatory's 4.3 m Discovery Channel Telescope and indicates that 2MASS J07414279-0506464 has a spectral type of L5.
  100. Lucey, J., Smith, R., Schechter, P., et al., (including Levine, S.), 2018, RNAAS, 2, 62, A New Quadruple-image Gravitational Lens in an Edge-on Disk Galaxy at z = 0.0956
    We report the serendipitous discovery of a quadruply-lensed source behind the z=0.095 edge-on disk galaxy 2MASXJ13170000-1405187, based on public imaging survey data from Pan-STARRS PS1 and the VISTA Hemisphere Survey. Follow-up imaging from Magellan/LDSS3 shows that the background source is spatially extended (i.e. not a QSO), and that two of the lensed images are observed through a prominent dust ring in the disk of the lens galaxy. We summarise results of preliminary modelling, which indicates an Einstein radius of 1.44 arcsec, and a K-band mass-to-light ratio of 0.5, relative to the solar value.
  101. Telfer, M., Parteli, E., Radebaugh, J., et al., (including Grundy, W.), 2018, Sci, 360, 992, Dunes on Pluto
    The surface of Pluto is more geologically diverse and dynamic than had been expected, but the role of its tenuous atmosphere in shaping the landscape remains unclear. We describe observations from the New Horizons spacecraft of regularly spaced, linear ridges whose morphology, distribution, and orientation are consistent with being transverse dunes. These are located close to mountainous regions and are orthogonal to nearby wind streaks. We demonstrate that the wavelength of the dunes (~0.4 to 1 kilometer) is best explained by the deposition of sand-sized (~200 to ~300 micrometer) particles of methane ice in moderate winds (<10 meters per second). The undisturbed morphology of the dunes, and relationships with the underlying convective glacial ice, imply that the dunes have formed in the very recent geological past.
  102. Malko, B., Hunter, D., 2018, AAS, 232, 218.01, Exploring the Surface Brightness Breaks and Star Formation in Disk Galaxies
    Stellar surface brightness profiles of both spirals and dwarf irregular galaxies often show breaks in which the exponential fall-off abruptly changes slope. Most often the profile is down-bending (Type II) in the outer disk, but sometimes it is up-bending (Type III). Stellar disks extend a long ways beyond the profile breaks, but we do not understand what happens physically at the breaks. To explore this we are examining the star formation activity, as traced with FUV emission, interior to the break compared to that exterior to the break in both dwarf irregulars and spiral galaxies. We present the results for the spiral galaxy NGC 2500 and compare it to the LITTLE THINGS dwarf irregular galaxies.
  103. Henden, A., Levine, S., Terrell, D., et al., 2018, AAS, 232, 223.06, APASS Data Release 10
    The AAVSO Photometric All-Sky Survey (APASS) has been underway since 2010. This survey covers the entire sky from 7.5 < V < 16.5 magnitude, and in the BVugrizY bandpasses. A northern and a southern site are used, each with twin ASA 20cm astrographs and Apogee Aspen CG16m cameras, covering 2.9x2.9 square degrees with 2.6arcsec pixels. Landolt and SDSS standards are used for all-sky solutions, with typical 0.02mag calibration errors on the bright end. DR9 is currently available through VizieR. DR10 is a complete reprocessing of all 500K images taken with the system, including hundreds of nights not part of DR9. Sextractor is used for star finding and centroiding; DAOPHOT is used for aperture photometry; the astrometry.net plate-solving library is used for basic astrometry, supplanted with more precise WCS that utilizes knowledge of the optical train distortions. With these changes, DR10 includes many more stars than prior releases. We describe the survey, its remaining limitations, and prospects for the future, including a very-bright-star extension.
  104. Thirouin, A., Sheppard, S., 2018, AJ, 155, 248, The Plutino Population: An Abundance of Contact Binaries
    We observed 12 Plutinos over two separated years with the 4.3 m Lowells Discovery Channel Telescope. Here, we present the first light-curve data for those objects. Three of them (2014 JL80, 2014 JO80, and 2014 JQ80) display a large light-curve amplitude explainable by a single elongated object, but they are most likely caused by a contact binary system due to their light-curve morphology. These potential contact binaries have rotational periods from 6.3 to 34.9 hr and peak-to-peak light-curve variability between 0.6 and 0.8 mag. We present partial light curves, allowing us to constrain the light-curve amplitude and the rotational period of another nine Plutinos. By merging our data with the literature, we estimate that up to 40% of the Plutinos could be contact binaries. Interestingly, we found that all of the suspected contact binaries in the 3:2 resonance are small with absolute magnitude H > 6 mag. Based on our sample and the literature, up to 50% of the small Plutinos are potential contact binaries.
  105. Harris, H., Dahn, C., Subasavage, J., et al., (including Levine, S.), 2018, AJ, 155, 252, Distances of Dwarf Carbon Stars
    Parallaxes are presented for a sample of 20 nearby dwarf carbon stars. The inferred luminosities cover almost two orders of magnitude. Their absolute magnitudes and tangential velocities confirm prior expectations that some originate in the Galactic disk, although more than half of this sample are halo stars. Three stars are found to be astrometric binaries, and orbital elements are determined; their semimajor axes are 1-3 au, consistent with the size of an AGB mass-transfer donor star.
  106. Trilling, D., Bellm, E., Malhotra, R., 2018, AJ, 155, 243, On the Detectability of Planet X with LSST
    Two planetary mass objects in the far outer solar systemcollectively referred to here as Planet X have recently been hypothesized to explain the orbital distribution of distant Kuiper Belt Objects. Neither planet is thought to be exceptionally faint, but the sky locations of these putative planets are poorly constrained. Therefore, a wide area survey is needed to detect these possible planets. The Large Synoptic Survey Telescope (LSST) will carry out an unbiased, large area (around 18000 deg2), deep (limiting magnitude of individual frames of 24.5) survey (the wide-fast-deep (WFD) survey) of the southern sky beginning in 2022, and it will therefore be an important tool in searching for these hypothesized planets. Here, we explore the effectiveness of LSST as a search platform for these possible planets. Assuming the current baseline cadence (which includes the WFD survey plus additional coverage), we estimate that LSST will confidently detect or rule out the existence of Planet X in 61% of the entire sky. At orbital distances up to 75 au, Planet X could simply be found in the normal nightly moving object processing; at larger distances, it will require custom data processing. We also discuss the implications of a nondetection of Planet X in LSST data.
  107. Grundy, W., Noll, K., Buie, M., et al., 2018, Icar, 305, 198, The upcoming mutual event season for the Patroclus-Menoetius Trojan binary
    We present new Hubble Space Telescope and ground-based Keck observations and new Keplerian orbit solutions for the mutual orbit of binary Jupiter Trojan asteroid (617) Patroclus and Menoetius, targets of NASA's Lucy mission. We predict event times for the upcoming mutual event season, which is anticipated to run from late 2017 through mid 2019.
  108. Cauley, P., Shkolnik, E., Llama, J., 2018, RNAAS, 2, 23, Transit Time Derivation for Hot Planet Bow-shocks
    We present an analytical estimate of hot planet bow-shock transit times that will be useful for planning observations of such signatures.
  109. Bannister, M., Gladman, B., Kavelaars, J., et al., (including Thirouin, A.), 2018, ApJS, 236, 18, OSSOS. VII. 800+ Trans-Neptunian ObjectsThe Complete Data Release
    The Outer Solar System Origins Survey (OSSOS), a wide-field imaging program in 2013-2017 with the Canada-France-Hawaii Telescope, surveyed 155 deg2 of sky to depths of m r = 24.1-25.2. We present 838 outer solar system discoveries that are entirely free of ephemeris bias. This increases the inventory of trans-Neptunian objects (TNOs) with accurately known orbits by nearly 50%. Each minor planet has 20-60 Gaia/Pan-STARRS-calibrated astrometric measurements made over 2-5 oppositions, which allows accurate classification of their orbits within the trans-Neptunian dynamical populations. The populations orbiting in mean-motion resonance with Neptune are key to understanding Neptunes early migration. Our 313 resonant TNOs, including 132 plutinos, triple the available characterized sample and include new occupancy of distant resonances out to semimajor axis a 130 au. OSSOS doubles the known population of the nonresonant Kuiper Belt, providing 436 TNOs in this region, all with exceptionally high-quality orbits of a uncertainty a 0.1% they show that the belt exists from a 37 au, with a lower perihelion bound of 35 au. We confirm the presence of a concentrated low-inclination a 44 au kernel population and a dynamically cold population extending beyond the 2:1 resonance. We finely quantify the surveys observational biases. Our survey simulator provides a straightforward way to impose these biases on models of the trans-Neptunian orbit distributions, allowing statistical comparison to the discoveries. The OSSOS TNOs, unprecedented in their orbital precision for the size of the sample, are ideal for testing concepts of the history of giant planet migration in the solar system.
  110. Neugent, K., Massey, P., Morrell, N., et al., (including Skiff, B.), 2018, AJ, 155, 207, A Runaway Yellow Supergiant Star in the Small Magellanic Cloud
    We recently discovered a yellow supergiant (YSG) in the Small Magellanic Cloud (SMC) with a heliocentric radial velocity of 300 km s-1, which is much larger than expected for a star at its location in the SMC. This is the first runaway YSG ever discovered and only the second evolved runaway star discovered in a galaxy other than the Milky Way. We classify the star as G5-8 I and use de-reddened broad-band colors with model atmospheres to determine an effective temperature of 4700 250 K, consistent with what is expected from its spectral type. The stars luminosity is then log L/L 4.2 0.1, consistent with it being a 30 Myr 9 M star according to the Geneva evolution models. The star is currently located in the outer portion of the SMCs body, but if the stars transverse peculiar velocity is similar to its peculiar radial velocity, in 10 Myr the star would have moved 1.6 across the disk of the SMC and could easily have been born in one of the SMCs star-forming regions. Based on its large radial velocity, we suggest it originated in a binary system where the primary exploded as a supernovae, thus flinging the runaway star out into space. Such stars may provide an important mechanism for the dispersal of heavier elements in galaxies given the large percentage of massive stars that are runaways. In the future, we hope to look into additional evolved runaway stars that were discovered as part of our other past surveys.

    This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

  111. Jenniskens, P., Baggaley, J., Crumpton, I., et al., (including Moskovitz, N.), 2018, P&SS, 154, 21, A survey of southern hemisphere meteor showers
    Results are presented from a video-based meteoroid orbit survey conducted in New Zealand between Sept. 2014 and Dec. 2016, which netted 24,906 orbits from +5 to -5 magnitude meteors. 44 new southern hemisphere meteor showers are identified after combining this data with that of other video-based networks. Results are compared to showers reported from recent radar-based surveys. We find that video cameras and radar often see different showers and sometimes measure different semi-major axis distributions for the same meteoroid stream. For identifying showers in sparse daily orbit data, a shower look-up table of radiant position and speed as a function of time was created. This can replace the commonly used method of identifying showers from a set of mean orbital elements by using a discriminant criterion, which does not fully describe the distribution of meteor shower radiants over time.
  112. Singer, K., Schenk, P., Beyer, R., et al., (including Grundy, W.), 2018, EGUGA, 5761, Cryovolcanism on Pluto and Charon
    When NASA's New Horizon spacecraft encountered the Pluto system on July 14, 2015 it revealed worlds with distinctive geologic histories and features. Signs of icy volcanic resurfacing are apparent on Pluto and Charon in the form of both smoother terrains and hummocky/blocky textured units, sometimes associated with very large topographic features. On Charon, the majority of the volcanism appears to have occurred early in its history, forming an extensive new surface on the southern part of the encounter hemisphere that erased most of the pre-existing topography. There are some signs of potential later, smaller episodes of volcanism on Charon (e.g., areas with lower crater densities). Pluto has several examples of more recent activity (with few-to-no superimposed craters), the most prominent being two enormous domes with deep central depressions. The informally named Wright Mons stands 4 km high and the main mound spans 150 km. The informally named Piccard Mons is 7 km high and 225 km wide. Only a few potential distinct flow features are evident, but the morphology of the areas surrounding Wright and Piccard indicates there may have been multiple episodes of terrain emplacement. There is also an extensive plateau to the west of Wright Mons with a relatively flat surface. This plateau exhibits many large depressions with various morphologies, most of which do not appear to have an impact origin. Each potential example of cryovolcanism found in the outer solar system is unique, and Pluto and Charon's features expand the information we have to understand this enigmatic process. We will present image, topographic, and composition data for these feature along with geologic mapping results. We will discuss potential formation mechanisms in light of available empirical and model constraints.
  113. Parteli, E., Telfer, M., Radebaugh, J., et al., (including Grundy, W.), 2018, EGUGA, 8689, Particle size and formative wind speed of transverse dunes at Sputnik Planitia, Pluto
    Images sent back to Earth by New Horizons revealed that the surface of Pluto is far more dynamic and geologically diverse than had been expected. However, the role of the tenuous atmosphere for landscape morphodynamics is still uncertain. Dunes, which require a supply of granular particles at the surface and a boundary layer of sufficient efficacy to enable direct entrainment of these particles by fluid forces, have been detected in surprising locations of our solar system. In particular, the equatorial regions of Saturn's moon Titan display a broad belt of linear dunes, while aeolian landforms also occur on the comet 67P Churyumov-Gerasimenko despite the lack of a persistent atmosphere on this comet. Here we describe regularly spaced, linear ridges on Pluto that have a morphology, orientation and distribution consistent with an interpretation as transverse dunes. The dunes occur proximal to mountainous regions in Sputnik Planitia, a plain of N2, CO and CH4 ice that extends across Pluto's tropics and covers 30 of longitude at its maximum. The transverse dunes are orthogonal to nearby wind streaks and display a crest-to-crest distance (wavelength) of 400 m - 1 km. We develop a model to approximately constrain average particle size (d) and formative wind speed (U) from the average crest-to-crest distance (wavelength ) of the transverse dunes. The relevant length-scale controlling this wavelength is the saturation length (Lsat) of the sediment flux, i.e. the distance needed by the sediment flux to adapt to a change in local flow conditions. By combining a mathematical model for as a function of Lsat and U with theory that predicts Lsat as a function of wind speed and attributes of sediment and atmosphere, we obtain the values of U and d that are consistent with . We find that the observed wavelength of Pluto transverse dunes is consistent with moderate winds (<10 m/s) and grain size that does not exceed 370 m and is most probably within the range between 210 and 310 m. This range of particle size is consistent with results from the spectral response of the MVIC CH4 filter, which predicts a granular medium of 200-300 m at Sputnik Planitia. From the lack of deformation of the dunes, as well as the relationships with the underlying convective glacial ice, we conclude that the dunes must have formed in the recent geological past.
  114. Thompson, S., Coughlin, J., Hoffman, K., et al., (including Dunham, E.), 2018, ApJS, 235, 38, Planetary Candidates Observed by Kepler. VIII. A Fully Automated Catalog with Measured Completeness and Reliability Based on Data Release 25
    We present the Kepler Object of Interest (KOI) catalog of transiting exoplanets based on searching 4 yr of Kepler time series photometry (Data Release 25, Q1-Q17). The catalog contains 8054 KOIs, of which 4034 are planet candidates with periods between 0.25 and 632 days. Of these candidates, 219 are new, including two in multiplanet systems (KOI-82.06 and KOI-2926.05) and 10 high-reliability, terrestrial-size, habitable zone candidates. This catalog was created using a tool called the Robovetter, which automatically vets the DR25 threshold crossing events (TCEs). The Robovetter also vetted simulated data sets and measured how well it was able to separate TCEs caused by noise from those caused by low signal-to-noise transits. We discuss the Robovetter and the metrics it uses to sort TCEs. For orbital periods less than 100 days the Robovetter completeness (the fraction of simulated transits that are determined to be planet candidates) across all observed stars is greater than 85%. For the same period range, the catalog reliability (the fraction of candidates that are not due to instrumental or stellar noise) is greater than 98%. However, for low signal-to-noise candidates between 200 and 500 days around FGK-dwarf stars, the Robovetter is 76.7% complete and the catalog is 50.5% reliable. The KOI catalog, the transit fits, and all of the simulated data used to characterize this catalog are available at the NASA Exoplanet Archive.
  115. Sacchi, E., Cignoni, M., Aloisi, A., et al., (including Hunter, D.), 2018, ApJ, 857, 63, Star Formation Histories of the LEGUS Dwarf Galaxies. II. Spatially Resolved Star Formation History of the Magellanic Irregular NGC 4449
    We present a detailed study of the Magellanic irregular galaxy NGC 4449 based on both archival and new photometric data from the Legacy Extragalactic UV Survey, obtained with the Hubble Space Telescope Advanced Camera for Surveys and Wide Field Camera 3. Thanks to its proximity (D = 3.82 0.27 Mpc), we reach stars 3 mag fainter than the tip of the red giant branch in the F814W filter. The recovered star formation history (SFH) spans the whole Hubble time, but due to the age-metallicity degeneracy of the red giant branch stars, it is robust only over the lookback time reached by our photometry, i.e., 3 Gyr. The most recent peak of star formation (SF) is around 10 Myr ago. The average surface density SF rate over the whole galaxy lifetime is 0.01 M yr-1 kpc-2. From our study, it emerges that NGC 4449 has experienced a fairly continuous SF regime in the last 1 Gyr, with peaks and dips whose SF rates differ only by a factor of a few. The very complex and disturbed morphology of NGC 4449 makes it an interesting galaxy for studies of the relationship between interactions and starbursts, and our detailed and spatially resolved analysis of its SFH does indeed provide some hints on the connection between these two phenomena in this peculiar dwarf galaxy.

    Based on observations obtained with the NASA/ESA Hubble Space Telescope at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy under NASA contract NAS 5-26555.

  116. Earle, A., Binzel, R., Young, L., et al., (including Grundy, W.), 2018, Icar, 303, 1, Albedo matters: Understanding runaway albedo variations on Pluto
    The data returned from NASA's New Horizons reconnaissance of the Pluto system show striking albedo variations from polar to equatorial latitudes as well as sharp longitudinal boundaries. Pluto has a high obliquity (currently 119) that varies by 23 over a period of less than 3 million years. This variation, combined with its regressing longitude of perihelion (360 over 3.7 million years), creates epochs of "Super Seasons" where one pole is pointed at the Sun at perihelion, thereby experiencing a short, relatively warm summer followed by its longest possible period of winter darkness. In contrast, the other pole experiences a much longer, less intense summer and a short winter season. We use a simple volatile sublimation and deposition model to explore the relationship between albedo variations, latitude, and volatile sublimation and deposition for the current epoch as well as historical epochs during which Pluto experienced these "Super Seasons." Our investigation quantitatively shows that Pluto's geometry creates the potential for runaway albedo and volatile variations, particularly in the equatorial region, which can sustain stark longitudinal contrasts like the ones we see between Tombaugh Regio and the informally named Cthulhu Regio.
  117. Cignoni, M., Sacchi, E., Aloisi, A., et al., (including Hunter, D.), 2018, ApJ, 856, 62, Star Formation Histories of the LEGUS Dwarf Galaxies. I. Recent History of NGC 1705, NGC 4449, and Holmberg II
    We use Hubble Space Telescope observations from the Legacy Extragalactic UV Survey to reconstruct the recent star formation histories (SFHs) of three actively star-forming dwarf galaxies, NGC 4449, Holmberg II, and NGC 1705, from their UV color-magnitude diagrams (CMDs). We apply a CMD fitting technique using two independent sets of stellar isochrones, PARSEC-COLIBRI and MIST, to assess the uncertainties related to stellar evolution modeling. Irrespective of the adopted stellar models, all three dwarfs are found to have had almost constant star formation rates (SFRs) in the last 100-200 Myr, with modest enhancements (a factor of 2) above the 100 Myr averaged SFR. Significant differences among the three dwarfs are found in terms of the overall SFR, the timing of the most recent peak, and the SFR/area. The initial mass function of NGC 1705 and Holmberg II is consistent with a Salpeter slope down to 5 M , whereas it is slightly flatter, s = -2.0, in NGC 4449. The SFHs derived with the two different sets of stellar models are consistent with each other, except for some quantitative details, attributable to their input assumptions. They also share the drawback that all synthetic diagrams predict a clear separation in color between the upper main-sequence and helium-burning stars, which is not apparent in the data. Since neither differential reddening, which is significant in NGC 4449, nor unresolved binaries appear to be sufficient to fill the gap, we suggest this calls for a revision of both sets of stellar evolutionary tracks.

    Based on observations obtained with the NASA/ESA Hubble Space Telescope at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy under NASA Contract NAS 5-26555.

  118. Kahre, L., Walterbos, R., Kim, H., et al., (including Hunter, D.), 2018, ApJ, 855, 133, Extinction Maps and Dust-to-gas Ratios in Nearby Galaxies with LEGUS
    We present a study of the dust-to-gas ratios in five nearby galaxies: NGC 628 (M74), NGC 6503, NGC 7793, UGC 5139 (Holmberg I), and UGC 4305 (Holmberg II). Using Hubble Space Telescope broadband WFC3/UVIS UV and optical images from the Treasury program Legacy ExtraGalactic UV Survey (LEGUS) combined with archival HST/Advanced Camera for Surveys data, we correct thousands of individual stars for extinction across these five galaxies using an isochrone-matching (reddening-free Q) method. We generate extinction maps for each galaxy from the individual stellar extinctions using both adaptive and fixed resolution techniques and correlate these maps with neutral H I and CO gas maps from the literature, including the H I Nearby Galaxy Survey and the HERA CO-Line Extragalactic Survey. We calculate dust-to-gas ratios and investigate variations in the dust-to-gas ratio with galaxy metallicity. We find a power-law relationship between dust-to-gas ratio and metallicity, consistent with other studies of dust-to-gas ratio compared to metallicity. We find a change in the relation when H2 is not included. This implies that underestimation of {N}{{{H}}2} in low-metallicity dwarfs from a too-low CO-to-H2 conversion factor X CO could have produced too low a slope in the derived relationship between dust-to-gas ratio and metallicity. We also compare our extinctions to those derived from fitting the spectral energy distribution (SED) using the Bayesian Extinction and Stellar Tool for NGC 7793 and find systematically lower extinctions from SED fitting as compared to isochrone matching.
  119. Radick, R., Lockwood, G., Henry, G., et al., (including Hall, J.), 2018, ApJ, 855, 75, Patterns of Variation for the Sun and Sun-like Stars
    We compare patterns of variation for the Sun and 72 Sun-like stars by combining total and spectral solar irradiance measurements between 2003 and 2017 from the SORCE satellite, Stromgren b, y stellar photometry between 1993 and 2017 from Fairborn Observatory, and solar and stellar chromospheric Ca II H+K emission observations between 1992 and 2016 from Lowell Observatory. The new data and their analysis strengthen the relationships found previously between chromospheric and brightness variability on the decadal timescale of the solar activity cycle. Both chromospheric H+K and photometric b, y variability among Sun-like stars are related to average chromospheric activity by power laws on this timescale. Young active stars become fainter as their H+K emission increases, and older, less active, more Sun-age stars tend to show a pattern of direct correlation between photometric and chromospheric emission variations. The directly correlated pattern between total solar irradiance and chromospheric Ca II emission variations shown by the Sun appears to extend also to variations in the Stromgren b, y portion of the solar spectrum. Although the Sun does not differ strongly from its stellar age and spectral class mates in the activity and variability characteristics that we have now studied for over three decades, it may be somewhat unusual in two respects: (1) its comparatively smooth, regular activity cycle, and (2) its rather low photometric brightness variation relative to its chromospheric activity level and variation, perhaps indicating that facular emission and sunspot darkening are especially well-balanced on the Sun.
  120. Sabbi, E., Calzetti, D., Ubeda, L., et al., (including Hunter, D.), 2018, ApJS, 235, 23, The Resolved Stellar Populations in the LEGUS Galaxies1
    The Legacy ExtraGalactic UV Survey (LEGUS) is a multiwavelength Cycle 21 Treasury program on the Hubble Space Telescope. It studied 50 nearby star-forming galaxies in 5 bands from the near-UV to the I-band, combining new Wide Field Camera 3 observations with archival Advanced Camera for Surveys data. LEGUS was designed to investigate how star formation occurs and develops on both small and large scales, and how it relates to the galactic environments. In this paper we present the photometric catalogs for all the apparently single stars identified in the 50 LEGUS galaxies. Photometric catalogs and mosaicked images for all filters are available for download. We present optical and near-UV color-magnitude diagrams for all the galaxies. For each galaxy we derived the distance from the tip of the red giant branch. We then used the NUV color-magnitude diagrams to identify stars more massive than 14 M , and compared their number with the number of massive stars expected from the GALEX FUV luminosity. Our analysis shows that the fraction of massive stars forming in star clusters and stellar associations is about constant with the star formation rate. This lack of a relation suggests that the timescale for evaporation of unbound structures is comparable or longer than 10 Myr. At low star formation rates this translates to an excess of mass in clustered environments as compared to model predictions of cluster evolution, suggesting that a significant fraction of stars form in unbound systems.

    Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA Inc., under NASA contract NAS 5-26555.

  121. Hunter, D., Gallardo, S., Zhang, H., et al., 2018, ApJ, 855, 7, A Study of Two Dwarf Irregular Galaxies with Asymmetrical Star Formation Distributions
    Two dwarf irregular galaxies, DDO 187 and NGC 3738, exhibit a striking pattern of star formation: intense star formation is taking place in a large region occupying roughly half of the inner part of the optical galaxy. We use data on the H I distribution and kinematics and stellar images and colors to examine the properties of the environment in the high star formation rate (HSF) halves of the galaxies in comparison with the low star formation rate halves. We find that the pressure and gas density are higher on the HSF sides by 30%-70%. In addition we find in both galaxies that the H I velocity fields exhibit significant deviations from ordered rotation and there are large regions of high-velocity dispersion and multiple velocity components in the gas beyond the inner regions of the galaxies. The conditions in the HSF regions are likely the result of large-scale external processes affecting the internal environment of the galaxies and enabling the current star formation there.
  122. Schaefer, G., Prato, L., Simon, M., 2018, AJ, 155, 109, Orbital Motion of Young Binaries in Ophiuchus and Upper Centaurus-Lupus
    We present measurements of the orbital positions and flux ratios of 17 binary and triple systems in the Ophiuchus star-forming region and the Upper Centaurus-Lupus cluster based on adaptive optics imaging at the Keck Observatory. We report the detection of visual companions in MML 50 and MML 53 for the first time, as well as the possible detection of a third component in WSB 21. For six systems in our sample, our measurements provide a second orbital position following their initial discoveries over a decade ago. For eight systems with sufficient orbital coverage, we analyze the range of orbital solutions that fit the data. Ultimately, these observations will help provide the groundwork toward measuring precise masses for these pre-main-sequence stars and understanding the distribution of orbital parameters in young multiple systems.
  123. Le Corre, L., Sanchez, J., Reddy, V., et al., (including Thirouin, A.), 2018, MNRAS, 475, 614, Ground-based characterization of Hayabusa2 mission target asteroid 162173 Ryugu: constraining mineralogical composition in preparation for spacecraft operations
    Asteroids that are targets of spacecraft missions are interesting because they present us with an opportunity to validate ground-based spectral observations. One such object is near-Earth asteroid (NEA) (162173) Ryugu, which is the target of the Japanese Space Agency's (JAXA) Hayabusa2 sample return mission. We observed Ryugu using the 3-m NASA Infrared Telescope Facility on Mauna Kea, Hawaii, on 2016 July 13 to constrain the object's surface composition, meteorite analogues, and link to other asteroids in the main belt and NEA populations. We also modelled its photometric properties using archival data. Using the Lommel-Seeliger model we computed the predicted flux for Ryugu at a wide range of viewing geometries as well as albedo quantities such as geometric albedo, phase integral, and spherical Bond albedo. Our computed albedo quantities are consistent with results from Ishiguro et al. Our spectral analysis has found a near-perfect match between our spectrum of Ryugu and those of NEA (85275) 1994 LY and Mars-crossing asteroid (316720) 1998 BE7, suggesting that their surface regoliths have similar composition. We compared Ryugu's spectrum with that of main belt asteroid (302) Clarissa, the largest asteroid in the Clarissa asteroid family, suggested as a possible source of Ryugu by Campins et al. We found that the spectrum of Clarissa shows significant differences with our spectrum of Ryugu, but it is similar to the spectrum obtained by Moskovitz et al. The best possible meteorite analogues for our spectrum of Ryugu are two CM2 carbonaceous chondrites, Mighei and ALH83100.
  124. Hindson, L., Kitchener, G., Brinks, E., et al., (including Hunter, D.), 2018, ApJS, 234, 29, A Radio Continuum Study of Dwarf Galaxies: 6 cm Imaging of LITTLE THINGS
    In this paper, we examine to what extent the radio continuum can be used as an extinction-free probe of star formation in dwarf galaxies. To that aim, we observe 40 nearby dwarf galaxies with the Very Large Array at 6 cm (4-8 GHz) in C-configuration. We obtained images with 3-8 resolution and noise levels of 3-15 Jy beam-1. We detected emission associated with 22 of the 40 dwarf galaxies, eight of which are new detections. The general picture is that of an interstellar medium largely devoid of radio continuum emission, interspersed by isolated pockets of emission associated with star formation. We find an average thermal fraction of 50%-70% and an average magnetic field strength of 5-8 G, only slightly lower than that found in larger, spiral galaxies. At 100 pc scales, we find surprisingly high values for the average magnetic field strength of up to 50 G. We find that dwarf galaxies follow the theoretical predictions of the radio continuum-star formation rate relation within regions of significant radio continuum emission but that the nonthermal radio continuum is suppressed relative to the star formation rate when considering the entire optical disk. We examine the far-infrared-star formation rate relation for our sample and find that the far-infrared is suppressed compared to the expected star formation rate. We discuss explanations for these observed relations and the impact of our findings on the radio continuum-far-infrared relation. We conclude that radio continuum emission at centimeter wavelengths has the promise of being a largely extinction-free star formation rate indicator. We find that star formation rates of gas-rich, low-mass galaxies can be estimated with an uncertainty of 0.2 dex between the values of 2 10-4 and 0.1 M yr-1.
  125. Oszkiewicz, D., Skiff, B., Moskovitz, N., et al., (including Marciniak, A.), 2018, A&A, 610, C3, Non-Vestoid candidate asteroids in the inner main belt (Corrigendum)
    No abstract found.
  126. Davis, B., Ciardullo, R., Feldmeier, J., et al., (including Jacoby, G.), 2018, RNAAS, 2, 32, The Planetary Nebula Luminosity Function (PNLF): Contamination from Supernova Remnants
    The planetary nebula luminosity function (PNLF) has been used as an extragalactic distance indicator since the 1980's, but there are still unsolved problems associated with its use. One of the most serious involves PNLF distances beyond ~ 10 Mpc, which tend to be slightly smaller than those of other methods. We consider the implications of previous spectroscopic investigations that found that several of the brightest planetary nebula (PN) candidates in M74 are actually compact supernova remnants (SNRs). Using narrow-band imaging data from the KPNO 4-m telescope, we measure the [O III] $\lambda$5007 and H$\alpha$ fluxes of all the known SNRs in M31 and M33, and test whether those objects could be misidentified as bright PNe at distances beyond ~ 10 Mpc. Our results suggest that compact SNRs are not an important source of contamination in photometric surveys for extragalactic PNe.
  127. Mace, G., Mann, A., Skiff, B., et al., (including Prato, L.), 2018, ApJ, 854, 145, Wolf 1130: A Nearby Triple System Containing a Cool, Ultramassive White Dwarf
    Following the discovery of the T8 subdwarf WISE J200520.38+542433.9 (Wolf 1130C), which has a proper motion in common with a binary (Wolf 1130AB) consisting of an M subdwarf and a white dwarf, we set out to learn more about the old binary in the system. We find that the A and B components of Wolf 1130 are tidally locked, which is revealed by the coherence of more than a year of V-band photometry phase-folded to the derived orbital period of 0.4967 days. Forty new high-resolution, near-infrared spectra obtained with the Immersion Grating Infrared Spectrometer provide radial velocities and a projected rotational velocity (v sin i) of 14.7 0.7 {km} {{{s}}}-1 for the M subdwarf. In tandem with a Gaia parallax-derived radius and verified tidal locking, we calculate an inclination of i = 29 2. From the single-lined orbital solution and the inclination we derive an absolute mass for the unseen primary ({1.24}-0.15+0.19 M ). Its non-detection between 0.2 and 2.5 m implies that it is an old (>3.7 Gyr) and cool (T eff < 7000 K) ONe white dwarf. This is the first ultramassive white dwarf within 25 pc. The evolution of Wolf 1130AB into a cataclysmic variable is inevitable, making it a potential SN Ia progenitor. The formation of a triple system with a primary mass >100 times the tertiary mass and the survival of the system through the common-envelope phase, where 80% of the system mass was lost, is remarkable. Our analysis of Wolf 1130 allows us to infer its formation and evolutionary history, which has unique implications for understanding low-mass star and brown dwarf formation around intermediate-mass stars.
  128. Marciniak, A., Bartczak, P., Muller, T., et al., (including Skiff, B.), 2018, A&A, 610, A7, Photometric survey, modelling, and scaling of long-period and low-amplitude asteroids
    Context. The available set of spin and shape modelled asteroids is strongly biased against slowly rotating targets and those with low lightcurve amplitudes. This is due to the observing selection effects. As a consequence, the current picture of asteroid spin axis distribution, rotation rates, radiometric properties, or aspects related to the object's internal structure might be affected too.
    Aims: To counteract these selection effects, we are running a photometric campaign of a large sample of main belt asteroids omitted in most previous studies. Using least chi-squared fitting we determined synodic rotation periods and verified previous determinations. When a dataset for a given target was sufficiently large and varied, we performed spin and shape modelling with two different methods to compare their performance.
    Methods: We used the convex inversion method and the non-convex SAGE algorithm, applied on the same datasets of dense lightcurves. Both methods search for the lowest deviations between observed and modelled lightcurves, though using different approaches. Unlike convex inversion, the SAGE method allows for the existence of valleys and indentations on the shapes based only on lightcurves.
    Results: We obtain detailed spin and shape models for the first five targets of our sample: (159) Aemilia, (227) Philosophia, (329) Svea, (478) Tergeste, and (487) Venetia. When compared to stellar occultation chords, our models obtained an absolute size scale and major topographic features of the shape models were also confirmed. When applied to thermophysical modelling (TPM), they provided a very good fit to the infrared data and allowed their size, albedo, and thermal inertia to be determined.
    Conclusions: Convex and non-convex shape models provide comparable fits to lightcurves. However, some non-convex models fit notably better to stellar occultation chords and to infrared data in sophisticated thermophysical modelling (TPM). In some cases TPM showed strong preference for one of the spin and shape solutions. Also, we confirmed that slowly rotating asteroids tend to have higher-than-average values of thermal inertia, which might be caused by properties of the surface layers underlying the skin depth.

    The photometric data is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr ( or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/610/A7

  129. Scholz, A., Llama, J., Muzic, K., et al., 2018, RNAAS, 2, 27, Discovery of a Magnetic White Dwarf with Unusual Short-period Variability
    We report the discovery of a magnetic white dwarf which shows periodic variability with P=110 min, color-dependent amplitudes and a transient phase shift in the blue compared to the red lightcurve - a previously unknown type of variability for this type of object. We attribute the variations either to a close ultracool (thus far undetected) companion or, more likely, to magnetic spots with unusual temperature structure.
  130. Biddle, L., Johns-Krull, C., Llama, J., et al., (including Prato, L., Skiff, B.), 2018, ApJL, 853, L34, K2 Reveals Pulsed Accretion Driven by the 2 Myr Old Hot Jupiter CI Tau b
    CI Tau is a young (2 Myr) classical T Tauri star located in the Taurus star-forming region. Radial velocity observations indicate it hosts a Jupiter-sized planet with an orbital period of approximately 9 days. In this work, we analyze time series of CI Taus photometric variability as seen by K2. The light curve reveals the stellar rotation period to be 6.6 days. Although there is no evidence that CI Tau b transits the host star, a 9 day signature is also present in the light curve. We believe this is most likely caused by planet-disk interactions that perturb the accretion flow onto the star, resulting in a periodic modulation of the brightness with the 9 day period of the planets orbit.
  131. Llama, J., Jardine, M., Wood, K., et al., 2018, ApJ, 854, 7, Simulating Radio Emission from Low-mass Stars
    Understanding the origins of stellar radio emission can provide invaluable insight into the strength and geometry of stellar magnetic fields and the resultant space weather environment experienced by exoplanets. Here, we present the first model capable of predicting radio emission through the electron cyclotron maser instability using observed stellar magnetic maps of low-mass stars. We determine the structure of the coronal magnetic field and plasma using spectropolarimetric observations of the surface magnetic fields and the X-ray emission measure. We then model the emission of photons from the locations within the corona that satisfy the conditions for electron cyclotron maser emission. Our model predicts the frequency and intensity of radio photons from within the stellar corona. We have benchmarked our model against the low-mass star V374 Peg. This star has both radio observations from the Very Large Array and a nearly simultaneous magnetic map. Using our model we are able to fit the radio observations of V374 Peg, providing additional evidence that the radio emission observed from low-mass stars may originate from the electron cyclotron maser instability. Our model can now be extended to all stars with observed magnetic maps to predict the expected frequency and variability of stellar radio emission in an effort to understand and guide future radio observations of low-mass stars.
  132. Jones, G., Knight, M., Battams, K., et al., 2018, SSRv, 214, 20, The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets
    This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all objects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun's centre, equal to half of Mercury's perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and tails are described, including dust, neutral and ionised gases, their chemical reactions, and their contributions to the near-Sun environment. Comet-solar wind interactions are discussed, including the use of comets as probes of solar wind and coronal conditions in their vicinities. We address the relevance of work on comets near the Sun to similar objects orbiting other stars, and conclude with a discussion of future directions for the field and the planned ground- and space-based facilities that will allow us to address those science topics.
  133. Baines, E., Armstrong, J., Schmitt, H., et al., (including van Belle, G.), 2018, AJ, 155, 30, Fundamental Parameters of 87 Stars from the Navy Precision Optical Interferometer
    We present the fundamental properties of 87 stars based on angular diameter measurements from the Navy Precision Optical Interferometer, 36 of which have not been measured previously using interferometry. Our sample consists of 5 dwarfs, 3 subgiants, 69 giants, 3 bright giants, and 7 supergiants, and span a wide range of spectral classes from B to M. We combined our angular diameters with photometric and distance information from the literature to determine each stars physical radius, effective temperature, bolometric flux, luminosity, mass, and age.
  134. Robbins, S., Runyon, K., Singer, K., et al., (including Grundy, W., Ennico, K.), 2018, JGRE, 123, 20, Investigation of Charon's Craters With Abrupt Terminus Ejecta, Comparisons With Other Icy Bodies, and Formation Implications
    On the moon and other airless bodies, ballistically emplaced ejecta transitions from a thinning, continuous inner deposit to become discontinuous beyond approximately one crater radius from the crater rim and can further break into discrete rays and secondary craters. In contrast, on Mars, ejecta often form continuous, distinct, and sometimes thick deposits that transition to a low ridge or escarpment that may be circular or lobate. The Martian ejecta type has been variously termed pancake, rampart, lobate, or layered, and in this work we refer to it as "abrupt termini" ejecta (ATE). Two main formation mechanisms have been proposed, one requiring interaction of the ejecta with the atmosphere and the other mobilization of near-surface volatiles. ATE morphologies are also unambiguously seen on Ganymede, Europa, Dione, and Tethys, but they are not as common as on Mars. We have identified up to 38 craters on Charon that show signs of ATE, including possible distal ramparts and lobate margins. These ejecta show morphologic and morphometric similarities with other moons in the solar system, which are a subset of the properties observed on Mars. From comparison of these ejecta on Charon and other solar system bodies, we find the strongest support for subsurface volatile mobilization and ejecta fluidization as the main formation mechanism for the ATE, at least on airless, icy worlds. This conclusion comes from the bodies on which they are found, an apparent preference for certain terrains, and the observation that craters with ATE can be near to similarly sized craters that only have gradational ejecta.
  135. Boyajian, T., Alonso, R., Ammerman, A., et al., (including von Braun, K.), 2018, ApJL, 853, L8, The First Post-Kepler Brightness Dips of KIC 8462852
    We present a photometric detection of the first brightness dips of the unique variable star KIC 8462852 since the end of the Kepler space mission in 2013 May. Our regular photometric surveillance started in 2015 October, and a sequence of dipping began in 2017 May continuing on through the end of 2017, when the star was no longer visible from Earth. We distinguish four main 1%-2.5% dips, named Elsie, Celeste, Skara Brae, and Angkor, which persist on timescales from several days to weeks. Our main results so far are as follows: (i) there are no apparent changes of the stellar spectrum or polarization during the dips and (ii) the multiband photometry of the dips shows differential reddening favoring non-gray extinction. Therefore, our data are inconsistent with dip models that invoke optically thick material, but rather they are in-line with predictions for an occulter consisting primarily of ordinary dust, where much of the material must be optically thin with a size scale 1 m, and may also be consistent with models invoking variations intrinsic to the stellar photosphere. Notably, our data do not place constraints on the color of the longer-term secular dimming, which may be caused by independent processes, or probe different regimes of a single process.
  136. Hunter, D., Melton, C., Leshin, S., et al., 2018, ApJ, 852, 114, Wide-field Imaging of the Environments of LITTLE THINGS Dwarf Irregular Galaxies
    We have obtained wide-field images of 36 of the 41 LITTLE THINGS (Local Irregulars That Trace Luminosity Extremes, The H I Nearby Galaxy Survey) nearby (<10.3 Mpc) dwarf irregular and blue compact dwarf galaxies. Although the LITTLE THINGS galaxies were chosen to be non-interacting and no companions were found in H I imaging, the purpose of this imaging was to search for optical companion galaxies that had been missed in imaging with smaller fields of view and that might indicate an external factor in ongoing star formation. The limiting magnitudes of the images range from 19.7 to 28.3 mag arcsec-2, with a median value of 25.9 mag arcsec-2. We did not find any unknown companions. Two of the LITTLE THINGS galaxies, NGC 4163 and NGC 4214, and the fainter dwarf, UGCA 276, lie potentially within 100 kpc of each other, but our imaging does not reveal any stellar bridge between the galaxies. This project was part of the Lowell Amateur Research Initiative.
  137. Schwamb, M., Fraser, W., Pike, R., et al., (including Thirouin, A.), 2018, AAS, 231, 115.03, Colours of the Outer Solar System Origins Survey: An Update
    The vast majority of the known dwarf-planet sized bodies are bright enough to be studied through optical and infrared spectroscopy. As a result, we have an understanding of the surface properties for the largest Kuiper belt objects (KBOs) which retain their primordial inventory of volatile ices. For the typically smaller > 22 mag KBO, we must rely instead on what colors reveal by proxy; yet this picture remains incomplete. Most KBO physical property studies examine the hodgepodge set of objects discovered by various surveys with different and varying detection biases that make it difficult if not impossible to reliably estimate the sizes of the different surface color groupings (compositional classes) residing in the modern-day Kuiper belt.The Colours of the Outer Solar System Origins Survey (Col-OSSOS) probes the surface properties within the Kuiper belt primarily through near simultaneous g,r and J colors with the Gemini North Telescope and u-band with Canada-France-Hawaii Telescope. The project aims to target ~100 KBOs brighter than 23.6 r mag found by the Outer Solar System Origins Survey (OSSOS), a survey with a well-measured detection efficiency. Thus, Col-OSSOS provides the first brightness-complete, compositional-dynamical map of the Outer Solar System, probing in a new light the radial color distribution in the primordial planetesimal disk from which KBOs originated. We will provide an update on the current status of the program highlighting results from the first two years of the survey; including size estimates of the two color KBO subgroups (the red and neutral surfaces) within the dynamically excited Kuiper belt and implications for the early planetesimal disk composition based on neutral-colored binaries found in the cold classical Kuiper belt.
  138. Hall, J., 2018, AAS, 231, 122.07, LED Street Lighting Solutions: Flagstaff, Arizona as a Case Study
    Dark-sky protection in Flagstaff, Arizona extends back to 1958, with the first ordinance in the City banning advertising floodlights. The current ordinance, adopted in 1989, is comprehensive and has played a critical role in maintaining the quality of the night sky for astronomy, tourism, public enjoyment, and other purposes. Flagstaff, like many communities around the world, is now working on a transition from legacy bulb-based technology to LED for its outdoor lighting. The City, Lowell Observatory, the U. S. Naval Observatory, and the Flagstaff Dark Skies Coalition have been working intensively for two years to identify an LED-based street lighting solution that will preserve the City's dark skies while meeting municipal needs. We will soon be installing test fixtures for an innovative solution incorporating narrow-band amber LED and modest amounts of low-CCT white LED. In this talk, I will review the types of LEDs available for outdoor lighting and discuss the plans for Flagstaff's street lighting in the LED era, which we hope will be a model for communities worldwide.
  139. Hall, J., 2018, AAS, 231, 142.04, A Regional, Multi-Stakeholder Collaboration for Dark-Sky Protection in Flagstaff, Arizona
    Flagstaff, Arizona is home to almost $200M in astronomical assets, including Lowell Observatory's 4.3-meter Discovery Channel Telescope and the Navy Precision Optical Interferometer, a partnership of Lowell, the U. S. Naval Observatory, and the Naval Research Laboratory. The City of Flagstaff and surrounding Coconino County have comprehensive and effective dark-sky ordinances, but continued regional growth has the potential to degrade the area's dark skies to a level at which observatory missions could be compromised. As a result, a wide array of stakeholders (the observatories, the City, the County, local dark-sky advocates, the business and tourism communities, the national parks and monuments, the Navajo Nation, the U. S. Navy, and others) have engaged in three complementary efforts to ensure that Flagstaff and Coconino County protect the area's dark skies while meeting the needs of the various communities and providing for continued growth and development. In this poster, I will present the status of Flagstaff's conversion to LED outdoor lighting, the Mission Compatibility Study carried out by the Navy to evaluate the dark-sky effects of buildout in Flagstaff, and the Joint Land Use Study (JLUS) presently underway among all the aforementioned stakeholders. Taken in sum, the efforts represent a comprehensive and constructive approach to dark-sky preservation region-wide, and they show what can be achieved when a culture of dark-sky protection is present and deliberate efforts are undertaken to maintain it for decades to come.
  140. Allen, L., Walker, C., Hall, J., et al., 2018, AAS, 231, 142.08, Protecting Dark Skies as a State-Wide Resource
    The state of Arizona contains the highest concentration of research telescopes in the continental United States, contributing more than a quarter of a billion dollars annually to the state's economy. Protecting the dark skies above these observatories is both good for astronomy and good for the state's economy. In this contribution we describe how a coalition of Arizona observatories is working together to protect our dark skies. Efforts date back to the creation of one of the first Outdoor Lighting Codes in the United States and continue today, including educational outreach, public policy engagement, and consensus building. We review some proven strategies, highlight recent successes and look at current threats.
  141. Lewis, B., Stansberry, J., Grundy, W., et al., 2018, AAS, 231, 144.03, Topographic and Other Influences on Pluto's Volatile Ices
    Plutos surface is known to consist of various volatile ices, mostly N2, CH4, and CO, which sublimate and condense on varying timescales, generally moving from points of high insolation to those of low insolation. The New Horizons Pluto encounter data provide multiple lenses through which to view Plutos detailed surface topography and composition and to investigate the distribution of volatiles on its surface, including albedo and elevation maps from the imaging instruments and composition maps from the LEISA spectral imager. The volatile surface ice is expected to be generally isothermal, due to the fact that their vapor pressures are in equilibrium with the atmosphere. Although secular topographic transport mechanisms suggest that points at low elevation should slowly fill with volatile ices (Trafton 2015 DPS abstract, Bertrand and Forget 2017), there are counter-examples of this across the surface, implying that energy discrepancies caused by insolation differences, albedo variations, local slopes, and other effects may take precedence at shorter timescales. Using data from the 2015 New Horizons flyby, we present our results of this investigation into the effects of variations in insolation, albedo, and topography on the presence of the different volatile ices across the surface of Pluto.
  142. Sullivan, K., Prato, L., Avilez, I., 2018, AAS, 231, 147.07, Veiling and Accretion Around the Young Binary Stars S and VV Corona Australis
    S CrA and VV CrA are two young binary star systems with separations of 170 AU and 250 AU, respectively, in the southern star-forming region Corona Australis. The spectral types of the four stars in these two systems are similar, approximately K7 to M1, hence the stellar masses are also similar. The study of young stars just emerging from their natal cloud cores at the very limits of observability allows us to probe the extreme environments in which planet formation begins to occur. Stars in this early evolutionary stage can have circumstellar or circumbinary disks, and sometimes remnants of the envelopes which surrounded them during the protostellar stage. Envelopes accrete onto disks and disks in turn accrete onto the central stars, triggering elevated continuum emission, line emission, outflows, and stellar winds. This violent stage marks the onset of the epoch of planet formation. Using high-resolution near-infrared, H-band spectroscopy from the Keck II telescope using the NIRSPEC instrument over 4-6 epochs, we are probing the chaotic environment surrounding the four stars in these systems. We determine the spectral types for VV CrA A and B for the first time, and examine the variable veiling and emission occurring around each of these stars. This research was supported in part by NSF grants AST-1461200 and AST-1313399.
  143. Prato, L., Nofi, L., 2018, AAS, 231, 156.03, The Lowell Observatory Predoctoral Scholar Program
    Lowell Observatory is pleased to solicit applications for our Predoctoral Scholar Fellowship Program. Now beginning its tenth year, this program is designed to provide unique research opportunities to graduate students in good standing, currently enrolled at Ph.D. granting institutions. Lowell staff research spans a wide range of topics, from astronomical instrumentation, to icy bodies in our solar system, exoplanet science, stellar populations, star formation, and dwarf galaxies. Strong collaborations, the new Ph.D. program at Northern Arizona University, and cooperative links across the greater Flagstaff astronomical community create a powerful multi-institutional locus in northern Arizona. Lowell Observatory's new 4.3 meter Discovery Channel Telescope is operating at full science capacity and boasts some of the most cutting-edge and exciting capabilities available in optical/infrared astronomy. Student research is expected to lead to a thesis dissertation appropriate for graduation at the doctoral level at the student's home institution. For more information, see http://www2.lowell.edu/rsch/predoc.php and links therein. Applications for Fall 2018 are due by May 1, 2018; alternate application dates will be considered on an individual basis.
  144. Baines, E., Armstrong, J., Schmitt, H., et al., (including van Belle, G.), 2018, AAS, 231, 157.01, The Fundamentals: Angular Diameter Measurements of 90 Stars from the NPOI
    We used the Navy Precision Optical Interferometer (NPOI) to measure the fundamental properties of 90 stars. The sample consists of 6 dwarfs, 3 subgiants, 71 giants, and 7 supergiants, and span a wide range of spectral classes from B to M. We combined our angular diameters with photometric and distance information from the literature to determine each star's physical radius, effective temperature, bolometric flux, luminosity, mass, and age. We present the results here.
  145. Shkolnik, E., Ardila, D., Barman, T., et al., (including Llama, J.), 2018, AAS, 231, 228.04, Monitoring the High-Energy Radiation Environment of Exoplanets Around Low-mass Stars with SPARCS (Star-Planet Activity Research CubeSat)
    Roughly seventy-five billion M dwarfs in our galaxy host at least one small planet in the habitable zone (HZ). The stellar ultraviolet (UV) radiation from M dwarfs is strong and highly variable, and impacts planetary atmospheric loss, composition and habitability. These effects are amplified by the extreme proximity of their HZs (0.1-0.4 AU). Knowing the UV environments of M dwarf planets will be crucial to understanding their atmospheric composition and a key parameter in discriminating between biological and abiotic sources for observed biosignatures. The Star-Planet Activity Research CubeSat (SPARCS) will be a 6U CubeSat devoted to photometric monitoring of M stars in the far-UV and near-UV, measuring the time-dependent spectral slope, intensity and evolution of M dwarf stellar UV radiation. For each target, SPARCS will observe continuously over at least one complete stellar rotation (5 - 45 days). SPARCS will also advance UV detector technology by flying high quantum efficiency, UV-optimized detectors developed at JPL. These Delta-doped detectors have a long history of deployment demonstrating greater than five times the quantum efficiency of the detectors used by GALEX. SPARCS will pave the way for their application in missions like LUVOIR or HabEx, including interim UV-capable missions. SPARCS will also be capable of target-of-opportunity UV observations for the rocky planets in M dwarf HZs soon to be discovered by NASAs TESS mission, providing the needed UV context for the first habitable planets that JWST will characterize.Acknowledgements: Funding for SPARCS is provided by NASAs Astrophysics Research and Analysis program, NNH16ZDA001N.
  146. Jacoby, G., Hillwig, T., De Marco, O., et al., 2018, AAS, 231, 241.04, Using Kepler K2 to Measure the Binary Fraction of PN Central Stars
    During the initial Kepler mission, 5 Planetary Nebula (PN) central stars were observed. The light curves for 4 of these central stars indicated a history of close binary interactions. That large fraction was suggestive that the actual fraction of PN harboring close binaries is much larger than the known lower limit of 20%, but that sample is far too small to be compelling. We have since acquired Kepler K2 data for Campaigns 0, 2, 7, and 11, hosting PN samples of 3, 4, 8, and 185 targets, respectively. We will provide an update on the number of binary candidates found in each field, and in particular, the Galactic Bulge field of Campaign 11. We also will discuss the challenges of working with Kepler observations in the crowded Campaign 11 field and the impact of those challenges on our ability to estimate the fraction of PN central stars that are binaries. This study was supported in part by NASA grants NNX17AE64G and NNX17AF80G.
  147. Davis, B., Ciardullo, R., Feldmeier, J., et al., (including Jacoby, G.), 2018, AAS, 231, 241.10, A Renewed Look at the Planetary Nebula Luminosity Function: Circumstellar Extinction and Contamination From Compact Supernova Remnants
    The planetary nebula luminosity function (PNLF) has been used as an extragalactic distance indicator since 1988, but there are still unsolved problems associated with its use. The two most serious involve PNLF distances beyond ~ 10 Mpc, which tend to be slightly smaller than those of other methods, and the lack of a theoretical explanation for the technique. We investigate these questions using a combination of narrow-band imaging data from the KPNO 4-m telescope, and recent LRS2 spectroscopy from the Hobby-Eberly Telescope.For the first project, we consider the implications of spectroscopic investigations by Kreckel et al. (2017), who found that in M74, several of the brightest planetary nebula (PN) candidates found by Herrmann et al. (2008) are actually compact supernova remnants (SNRs). First, we measure the [O III] and H-alpha fluxes of all the known SNRs in M31 and M33, and test whether those objects could be misidentified as bright PNe at distances beyond ~ 8 Mpc. We also obtain spectroscopy of bright PN candidates in the Fireworks Galaxy, NGC 6946, to test for PN/SNR confusion via the strengths of the [N II] and [S II] emission lines. Both experiments suggest that compact supernova remnants are not an important source of contamination in photometric surveys for extragalactic PNe.For the second project, we, for the first time, determine the de-reddened PNLF of an old stellar population. By performing spectroscopy of the brightest PN in M31s bulge and measuring the objects Balmer decrements, we remove the effects of circumstellar extinction and derive the true location of the PNLFs bright-end cutoff. In future studies, these data can be used to directly test the latest PNLF models, which combine modern post-AGB stellar evolutionary tracks with the physics of expanding nebulae.
  148. Prato, L., Avilez, I., Lindstrom, K., et al., (including Graham, S., Biddle, L., Skiff, B., Nofi, L.), 2018, AAS, 231, 339.12, The Young Visual Binary Survey
    Differences in the stellar and circumstellar properties of the components of young binaries provide key information about star and disk formation and evolution processes. Because objects with separations of a few to a few hundred astronomical units share a common environment and composition, multiple systems allow us to control for some of the factors which play into star formation. We are completing analysis of a rich sample of about 100 pre-main sequence binaries and higher order multiples, primarily located in the Taurus and Ophiuchus star forming regions. This poster will highlight some of out recent, exciting results. All reduced spectra and the results of our analysis will be publicly available to the community at http://jumar.lowell.edu/BinaryStars/. Support for this research was provided in part by NSF award AST-1313399 and by NASA Keck KPDA funding.
  149. Berger, C., Hunter, D., 2018, AAS, 231, 340.03, Exploring Properties of HI Clouds in Dwarf Irregular Galaxies
    Dwarf Irregular galaxies form stars and maintain exponential stellar disks at extremely low gas densities. One proposed method of maintaining such regular outer disks is scattering stars off of HI clouds. In order to understand the processes present in dwarf irregular stellar disks, we present a survey of atomic hydrogen clouds in and around a subset of representative galaxies from the LITTLE THINGS survey. We apply a cloud identification program to the 21 cm HI line emission cubes and extract masses, radii, surface densities, and distances from the center of the galaxy in the plane of the galaxy of each cloud. Our data show a wide range of clouds characterized by low surface densities but varied in mass and size. The number of clouds found and the mass of the most massive cloud show no correlation to integrated star forming rates or luminosity in these galaxies. However, they will be used as input for models of stars scattering off of HI clouds to better understand the regular stellar disks in dwarf Irregular galaxies.We acknowledge support from the National Science Foundation grant AST-1461200 to Northern Arizona University for Research Experiences for Undergraduates summer internships.
  150. Gunshefski, L., Paust, N., van Belle, G., 2018, AAS, 231, 348.15, Investigating Open Clusters Melotte 111 and NGC 6811
    We present photometry and color-magnitude diagrams for the open clusters Melotte 111 (Coma Bernices) and NGC 6811. These clusters were observed with Lowell Observatorys Discovery Channel Telescope Large Monolithic Imager in the V and I bands. The images were reduced with IRAF and photometry was performed with DAOPHOT/ALLSTAR. The resulting photometry extends many magnitudes below the main sequence turnoff. Both clusters are located nearby, (Melotte 111 d=86 pc and NGC 6811 d=1,107) and are evolutionarily young (Melotte 111, age=450 Myr and NGC 6811, age=1,000 Myr). This work marks the first step of a project to determine the cluster main sequence mass functions and examine how the mass functions evolve in young stellar populations.
  151. Neugent, K., Massey, P., Morrell, N., 2018, AAS, 231, 349.03, A Runaway Yellow Supergiant Star in the Small Magellanic Cloud
    Around 35% of OB stars are thought to be runaways formed through supernova explosions of companions, interactions with black holes, or close encounters with neighboring stars. Once these OB stars begin running away from their birthplace they eventually begin to evolve. However, few runaway evolved massive stars have been found, especially in galaxies other than the Milky Way. We recently stumbled across a Yellow Supergiant (YSG) in the Small Magellanic Cloud (SMC) with a heliocentric radial velocity ~150 km/s larger than expected. This velocity suggests that over the course of 10 million years, the YSG has moved 1.6 degrees across the plane of the SMC. A visual inspection of the locations of YSGs within the SMC shows that this star is on the outer edge of where the YSGs are located and not in an OB association. Runaway stars are also associated with bow shocks and this is primarily how such stars have been detected before. At a distance of the SMC, a bow shock would extend 2.8" away from the star and should be detectable using ground based telescopes. We have plans to search for such a bow shock and should know the results by the time of the meeting.
  152. van Belle, G., von Braun, K., Horch, E., et al., (including Clark, C.), 2018, AAS, 231, 349.31, The POKEMON Speckle Survey of Nearby M-Dwarfs
    The POKEMON (Pervasive Overview of Kompanions of Every M-dwarf in Our Neighborhood) survey of nearby M-dwarfs intends to inspect, at diffraction-limited resolution, every low-mass star out to 15pc, along with selected additional objects to 25pc. The primary emphasis of the survey is detection of low-mass companions to these M-dwarfs for refinement of the low-mass star multiplicity rate. The resultant catalog of M-dwarf companions will also guide immediate refinement of transit planet detection results from surveys such as TESS. POKEMON is using Lowell Observatory's 4.3-m Discovery Channel Telescope (DCT) with the Differential Speckle Survey Instrument (DSSI) speckle camera, along with the NN-Explore Exoplanet Stellar Speckle Imager (NESSI) speckle imager on 3.5-m WIYN; the survey takes advantage of the extremely rapid observing cadence rates possible with WIYN and (especially) DCT. The current status and preliminary results from the first 20+ nights of observing will be presented. Gotta observe them all!
  153. Armstrong, J., Schmitt, H., Baines, E., et al., (including van Belle, G.), 2018, AAS, 231, 442.06, The NPOI: an Update on the Upgrades
    The NPOI is in the process of adding three AO-equipped moveable 1-meter telescopes, and in the initial stages of adding an infrared beam combiner. Two of the 1-m telescope stations planned will form a 432-m baseline. Hardware upgrades including advanced delay line controllers and improved cameras for the VISION beam combiner are under way, and an improved angle tracking system has been designed and is in the process of acquisition. For 2018, we also plan to integrate our Long Delay Lines, giving delay in discrete increments of 25 m. We will describe the state of these upgrades, as well as highlight some recent results.
  154. Llama, J., Jardine, M., 2018, AAS, 231, 450.03, Simulating Electron Cyclotron Maser Emission for Low Mass Stars
    Zeeman-Doppler Imaging (ZDI) is a powerful technique that enables us to map the large-scale magnetic fields of stars spanning the pre- and main-sequence. Coupling these magnetic maps with field extrapolation methods allow us to investigate the topology of the closed, X-ray bright corona, and the cooler, open stellar wind.Using ZDI maps of young M dwarfs with simultaneous radio light curves obtained from the VLA, we present the results of modeling the Electron-Cyclotron Maser (ECM) emission from these systems. We determine the X-ray luminosity and ECM emission that is produced using the ZDI maps and our field extrapolation model. We compare these findings with the observed radio light curves of these stars. This allows us to predict the relative phasing and amplitude of the stellar X-ray and radio light curves.This benchmarking of our model using these systems allows us to predict the ECM emission for all stars that have a ZDI map and an observed X-ray luminosity. Our model allows us to understand the origin of transient radio emission observations and is crucial for disentangling stellar and exoplanetary radio signals.
  155. Wood, C., Boyajian, T., Crepp, J., et al., (including von Braun, K.), 2018, AAS, 231, 450.05, Precise Ages for the Benchmark Brown Dwarfs HD 19467 B and HD 4747 B
    Large uncertainty in the age of brown dwarfs, stemming from a mass-age degeneracy, makes it difficult to constrain substellar evolutionary models. To break the degeneracy, we need ''benchmark" brown dwarfs (found in binary systems) whose ages can be determined independent of their masses. HD~19467~B and HD~4747~B are two benchmark brown dwarfs detected through the TRENDS (TaRgeting bENchmark objects with Doppler Spectroscopy) high-contrast imaging program for which we have dynamical mass measurements. To constrain their ages independently through isochronal analysis, we measured the radii of the host stars with interferometry using the Center for High Angular Resolution Astronomy (CHARA) Array. Assuming the brown dwarfs have the same ages as their host stars, we use these results to distinguish between several substellar evolutionary models. In this poster, we present new age estimates for HD~19467 and HD~4747 that are more accurate and precise and show our preliminary comparisons to cooling models.
  156. Rector, T., Shuping, R., Prato, L., et al., 2018, ApJ, 852, 13, The Discovery of Herbig-Haro Objects in LDN 673
    We report the discovery of 12 faint Herbig-Haro (HH) objects in LDN 673 found using a novel color-composite imaging method that reveals faint H emission in complex environments. Follow-up observations in [S II] confirmed their classification as HH objects. Potential driving sources are identified from the Spitzer c2d Legacy Program catalog and other infrared observations. The 12 new HH objects can be divided into three groups: four are likely associated with a cluster of eight young stellar object class I/II IR sources that lie between them; five are colinear with the T Tauri multiple star system AS 353, and are likely driven by the same source as HH 32 and HH 332 and three are bisected by a very red source that coincides with an infrared dark cloud. We also provide updated coordinates for the three components of HH 332. Inaccurate numbers were given for this object in the discovery paper. The discovery of HH objects and associated driving sources in this region provides new evidence for star formation in the Aquila clouds, implying a much larger T Tauri population in a seldom-studied region.
  157. Prato, L., Ruiz-Rodriguez, D., Wasserman, L., 2018, ApJ, 852, 38, Orbital Solution for the Spectroscopic Binary in the GW Ori Hierarchical Triple
    We present the first double-lined orbital solution for the close binary in the GW Ori triple system. Using 12 epochs of infrared spectroscopy, we detected the lines of both stars in the inner pair, previously known as single-lined only. Our preliminary infrared orbital solution has an eccentricity of e = 0.21 0.10, a period of P = 241.15 0.72 days, and a mass ratio of q = 0.66 0.13. We find a larger semi-amplitude for the primary star, K1 = 6.57 1.00 km s-1, with an infrared-only solution compared to K1 = 4.41 0.33 km s-1 with optical data from the literature, likely the result of line blending and veiling in the optical. The component spectral types correspond to G3 and K0 stars, with v\sin i values of 43 km s-1 and 50 km s-1, respectively. We obtained a flux ratio of = 0.58 0.14 in the H-band, allowing us to estimate individual masses of 3.2 and 2.7 M for the primary and secondary, respectively, using evolutionary tracks. The tracks also yield a coeval age of 1 Myr for both components to within 1. GW Ori is surrounded by a circumbinary/circumtriple disk. A tertiary component has been detected in previous studies; however, we did not detect this component in our near-infrared spectra, probably the result of its relative faintness and blending in the absorption lines of these rapidly rotating stars. With these results, GW Ori joins the small number of classical T Tauri, double-lined spectroscopic binaries.
  158. Adams, A., Boyajian, T., von Braun, K., 2018, MNRAS, 473, 3608, Predicting stellar angular diameters from V, IC, H and K photometry
    Determining the physical properties of microlensing events depends on having accurate angular sizes of the source star. Using long baseline optical interferometry, we are able to measure the angular sizes of nearby stars with uncertainties 2 per cent. We present empirically derived relations of angular diameters which are calibrated using both a sample of dwarfs/subgiants and a sample of giant stars. These relations are functions of five colour indices in the visible and near-infrared, and have uncertainties of 1.8-6.5 per cent depending on the colour used. We find that a combined sample of both main-sequence and evolved stars of A-K spectral types is well fitted by a single relation for each colour considered. We find that in the colours considered, metallicity does not play a statistically significant role in predicting stellar size, leading to a means of predicting observed sizes of stars from colour alone.
  159. Dalle Ore, C., Protopapa, S., Cook, J., et al., (including Grundy, W.), 2018, Icar, 300, 21, Ices on Charon: Distribution of H2O and NH3 from New Horizons LEISA observations
    Charon, the largest moon of Pluto, appeared as a fairly homogeneous, gray, icy world to New Horizons during closest approach on July 14th, 2015. Charon's sub-Pluto hemisphere was scanned by the Ralph/LEISA near-IR spectrograph providing an unprecedented opportunity to measure its surface composition. We apply a statistical clustering tool to identify spectrally distinct terrains and a radiative transfer approach to study the variations of the 2.0-m H2O ice band. We map the distribution of the ices previously reported to be present on Charon's surface, namely H2O and the products of NH3 in H2O. We find that H2O ice is mostly in the crystalline phase, confirming previous studies. The regions with the darkest albedos show the strongest signature of amorphous-phase ice, although the crystalline component is still strong. The brighter albedo regions, often corresponding to crater ejecta blankets, are characterized by larger H2O grains, possibly an indication of a younger age. We observe two different behaviors for the two absorption bands representing NH3 in H2O. The 2.21-m band tends to cluster more in the northern areas compared to the 2.01-m band. Both bands are present in the brighter crater rays, but not all craters show both bands. The 2.21-m band is also clearly present on the smaller moons Hydra and Nix. These results hint that different physical conditions may determine the appearance or absence of these two different forms of NH3 in H2O ice in the Pluto system. We also investigate the blue slope affecting the spectrum at wavelengths longer than 1.8 m previously reported by several authors. We find that the slope is common among the objects in the Pluto system, Charon, the smaller moons Nix and Hydra, and the darkest terrains on Pluto. It also characterizes the analog ice tholin obtained from irradiation of Pluto-specific materials (a mixture of N2, CH4, and CO ices) in the laboratory. Our modeling results show that Pluto ice tholins are widespread almost uniformly on Charon suggesting a common distribution possibly part of the original reservoir of materials that made up Charon. This was irradiated over the years to yield the gray color characteristic of Charon today. On top of the 'primordial' Pluto ice tholin there is the redder component produced by irradiation of the CH4 provided by Pluto's atmospheric contribution as illustrated by Grundy et al. (2016a).
  160. Moore, J., Howard, A., Umurhan, O., et al., (including Grundy, W.), 2018, Icar, 300, 129, Bladed Terrain on Pluto: Possible origins and evolution
    Bladed Terrain on Pluto consists of deposits of massive CH4, which are observed to occur within latitudes 30 of the equator and are found almost exclusively at the highest elevations (> 2 km above the mean radius). Our analysis indicates that these deposits of CH4 preferentially precipitate at low latitudes where net annual solar energy input is lowest. CH4 and N2 will both precipitate at low elevations. However, since there is much more N2 in the atmosphere than CH4, the N2 ice will dominate at these low elevations. At high elevations the atmosphere is too warm for N2 to precipitate so only CH4 can do so. We conclude that following the time of massive CH4 emplacement; there have been sufficient excursions in Pluto's climate to partially erode these deposits via sublimation into the blades we see today. Blades composed of massive CH4 ice implies that the mechanical behavior of CH4 can support at least several hundred meters of relief at Pluto surface conditions. Bladed Terrain deposits may be widespread in the low latitudes of the poorly seen sub-Charon hemisphere, based on spectral observations. If these locations are indeed Bladed Terrain deposits, they may mark heretofore unrecognized regions of high elevation.
  161. Harper, D., Runyan, M., Dowell, C., et al., (including Hamilton, R.), 2018, JAI, 7, 1840008-1025, HAWC+, the Far-Infrared Camera and Polarimeter for SOFIA
    High-resolution Airborne Wide-band Camera (HAWC+) is the facility far-infrared imager and polarimeter for SOFIA, NASAs Stratospheric Observatory for Infrared Astronomy. It is designed to cover the portion of the infrared spectrum that is completely inaccessible to ground-based observatories and which is essential for studies of astronomical sources with temperatures between tens and hundreds of degrees Kelvin. Its ability to make polarimetric measurements of aligned dust grains provides a unique new capability for studying interstellar magnetic fields. HAWC+ began commissioning flights in April 2016 and was accepted as a facility instrument in early 2018. In this paper, we describe the instrument, its operational procedures, and its performance on the observatory.
  162. Shkolnik, E., Llama, J., 2018, haex, 20, Signatures of Star-Planet Interactions
    Planets interact with their host stars through gravity, radiation, and magnetic fields, and for those giant planets that orbit their stars within 10 stellar radii (0.1 AU for a sun-like star), star-planet interactions (SPI) are observable with a wide variety of photometric, spectroscopic, and spectropolarimetric studies. At such close distances, the planet orbits within the sub-Alfvenic radius of the star in which the transfer of energy and angular momentum between the two bodies is particularly efficient. The magnetic interactions appear as enhanced stellar activity modulated by the planet as it orbits the star rather than only by stellar rotation. These SPI effects are informative for the study of the internal dynamics and atmospheric evolution of exoplanets. The nature of magnetic SPI is modeled to be strongly affected by both the stellar and planetary magnetic fields, possibly influencing the magnetic activity of both, as well as affecting the irradiation and even the migration of the planet and rotational evolution of the star. As phase-resolved observational techniques are applied to a large statistical sample of hot Jupiter systems, extensions to other tightly orbiting stellar systems, such as smaller planets close to M dwarfs become possible. In these systems, star-planet separations of tens of stellar radii begin to coincide with the radiative habitable zone where planetary magnetic fields are likely a necessary condition for surface habitability.
  163. Dunham, E., 2018, haex, 170, Discovery of the First Transiting Planets
    Early thinking about detecting extrasolar planets was largely circumscribed by the expectation that other solar systems would be similar to our own, the only known example at the time. Given this mind-set, transit detections were expected to be exceedingly difficult for small planets and rarely seen for larger ones. The discovery of 51 Peg and subsequent hot Jupiters by the radial velocity method completely upended our thinking - transits were suddenly practical, perhaps even easy! This immediately led to follow-up searches for transits in systems discovered by the radial velocity technique and, conversely, to wide-field ground-based transit search programs with radial velocity follow-up observations. As is usually the case, transit work turned out to be harder than initially expected but was still possible and productive. This chapter reviews the circumstances leading to the first transit observations of HD 209458, the early OGLE exoplanets, and TrES-1 and TrES-2, as well as some of the frustrations and difficulties encountered along the way.
  164. Olkin, C., Grundy, W., 2018, oss, 3, A Survey of Pluto's Surface Composition
    No abstract found.
  165. 164 publications and 2290 citations in 2018.

164 publications and 2290 citations total.