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Research involving Lowell Observatory staff 2017
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Years: 2017 Bottom

    2017

  1. Thirouin, A., Sheppard, S., 2017, AJ, 154, 241, A Possible Dynamically Cold Classical Contact Binary: (126719) 2002 CC249
    Images of the Kuiper Belt object (126719) 2002 CC249 obtained in 2016 and 2017 using the 6.5 m Magellan-Baade Telescope and the 4.3 m Discovery Channel Telescope are presented. A light curve with a periodicity of 11.87 0.01 hr and a peak-to-peak amplitude of 0.79 0.04 mag is reported. This high amplitude double-peaked light curve can be due to a single elongated body, but it is best explained by a contact binary system from its U-/V-shaped light curve. We present a simple full-width-at-half-maximum test that can be used to determine if an object is likely a contact binary or an elongated object based on its light curve. Considering that 2002 CC249 is in hydrostatic equilibrium, a system with a mass ratio qmin = 0.6, and a density min = 1 g cm-3, or less plausible a system with qmax = 1, and max = 5 g cm-3 can interpret the light curve. Assuming a single Jacobi ellipsoid in hydrostatic equilibrium and an equatorial view, we estimate 0.34 g cm-3, and a/b = 2.07. Finally, we report a new color study showing that 2002 CC249 displays an ultra red surface characteristic of a dynamically Cold Classical trans-Neptunian object.
  2. Grunblatt, S., Huber, D., Gaidos, E., et al., (including Nofi, L.), 2017, AJ, 154, 254, Seeing Double with K2: Testing Re-inflation with Two Remarkably Similar Planets around Red Giant Branch Stars
    Despite more than 20 years since the discovery of the first gas giant planet with an anomalously large radius, the mechanism for planet inflation remains unknown. Here, we report the discovery of K2-132b, an inflated gas giant planet found with the NASA K2 Mission, and a revised mass for another inflated planet, K2-97b. These planets orbit on 9 day orbits around host stars that recently evolved into red giants. We constrain the irradiation history of these planets using models constrained by asteroseismology and Keck/High Resolution Echelle Spectrometer spectroscopy and radial velocity measurements. We measure planet radii of 1.31 0.11 RJ and 1.30 0.07 RJ, respectively. These radii are typical for planets receiving the current irradiation, but not the former, zero age main-sequence irradiation of these planets. This suggests that the current sizes of these planets are directly correlated to their current irradiation. Our precise constraints of the masses and radii of the stars and planets in these systems allow us to constrain the planetary heating efficiency of both systems as 0.03 %-0.02%0.03%. These results are consistent with a planet re-inflation scenario, but suggest that the efficiency of planet re-inflation may be lower than previously theorized. Finally, we discuss the agreement within 10% of the stellar masses and radii, and the planet masses, radii, and orbital periods of both systems, and speculate that this may be due to selection bias in searching for planets around evolved stars.
  3. Olkin, C., Spencer, J., Grundy, W., et al., 2017, AJ, 154, 258, The Global Color of Pluto from New Horizons
    The New Horizons flyby provided the first high-resolution color maps of Pluto. We present here, for the first time, an analysis of the color of the entire sunlit surface of Pluto and the first quantitative analysis of color and elevation on the encounter hemisphere. These maps show the color variation across the surface from the very red terrain in the equatorial region, to the more neutral colors of the volatile ices in Sputnik Planitia, the blue terrain of East Tombaugh Regio, and the yellow hue on Pluto's North Pole. There are two distinct color mixing lines in the color-color diagrams derived from images of Pluto. Both mixing lines have an apparent starting point in common: the relatively neutral-color volatile-ice covered terrain. One line extends to the dark red terrain exemplified by Cthulhu Regio and the other extends to the yellow hue in the northern latitudes. There is a latitudinal dependence of the predominant color mixing line with the most red terrain located near the equator, less red distributed at mid-latitudes and more neutral terrain at the North Pole. This is consistent with the seasonal cycle controlling the distribution of colors on Pluto. Additionally, the red color is consistent with tholins. The yellow terrain (in the false color images) located at the northern latitudes occurs at higher elevations.
  4. Torres, G., Kane, S., Rowe, J., et al., (including Horch, E.), 2017, AJ, 154, 264, Validation of Small Kepler Transiting Planet Candidates in or near the Habitable Zone
    A main goal of NASA's Kepler Mission is to establish the frequency of potentially habitable Earth-size planets (\oplus). Relatively few such candidates identified by the mission can be confirmed to be rocky via dynamical measurement of their mass. Here we report an effort to validate 18 of them statistically using the BLENDER technique, by showing that the likelihood they are true planets is far greater than that of a false positive. Our analysis incorporates follow-up observations including high-resolution optical and near-infrared spectroscopy, high-resolution imaging, and information from the analysis of the flux centroids of the Kepler observations themselves. Although many of these candidates have been previously validated by others, the confidence levels reported typically ignore the possibility that the planet may transit a star different from the target along the same line of sight. If that were the case, a planet that appears small enough to be rocky may actually be considerably larger and therefore less interesting from the point of view of habitability. We take this into consideration here and are able to validate 15 of our candidates at a 99.73% (3) significance level or higher, and the other three at a slightly lower confidence. We characterize the GKM host stars using available ground-based observations and provide updated parameters for the planets, with sizes between 0.8 and 2.9 R. Seven of them (KOI-0438.02, 0463.01, 2418.01, 2626.01, 3282.01, 4036.01, and 5856.01) have a better than 50% chance of being smaller than 2 R and being in the habitable zone of their host stars.
  5. Parker, A., Howett, C., Olkin, C., et al., (including Grundy, W.), 2017, AGUFM, 2017, P11C-2520, Constraining Aerosol Properties with the Spectrally-Resolved Phase Function of Pluto's Hazes
    The Multi-spectral Visible Imaging Camera (MVIC) and Lisa Hardaway Infrared Mapping Spectrometer (LEISA) aboard New Horizons imaged Pluto at high phase throughout departure from the system in July of 2015. The repeated MVIC color scans captured the phase behavior of Pluto's atmospheric hazes through phase angles of 165.0 to 169.5 degrees in four bandpasses in the visible and NIR. A spatially-resolved departure LEISA scan delivered moderate SNR NIR spectra of the hazes over wavelengths from 1.25 - 2.5 microns. Here we present our analysis of the departure MVIC and LEISA data, extracting high precision color phase curves of the hazes using the most up-to-date radiometric calibration and NIR gain drift corrections. We interpret these phase curves and spectra using Mie theory to constrain the size and composition of haze particles, with results indicating broad similarity to Titan aerosol analogues ("tholins"). Finally, we will explore the implications of the nature of these haze particles for the evolution of Pluto's surface as they settle out onto it over time.
  6. Umurhan, O., Howard, A., White, O., et al., (including Grundy, W.), 2017, AGUFM, 2017, P11C-2522, Pluto's Paleoglaciation: Processes and Bounds.
    New Horizons imaging of Pluto's surface shows eroded landscapes reminiscent of assorted glaciated terrains found on the Earth such as alpine valleys, dendritic networks and others. For example, LORRI imaging of fluted craters show radially oriented ridging which also resembles Pluto's washboard terrain. Digital elevation modeling indicates that these down-gradient oriented ridges are about 3-4 km spaced apart with depths ranging from 0.2-0.5 km. Present day glaciation on Pluto is characterized by moving N2 ice blocks presumably riding over a H2O ice bedrock substrate. Assuming Pluto's ancient surface was sculpted by N2 glaciation, what remains a mystery is the specific nature of the glacial erosion mechanism(s) responsible for the observed features. To better resolve this puzzle, we perform landform evolution modeling of several glacial erosion processes known from terrestrial H2O ice glaciation studies. These terrestrial processes, which depend upon whether or not the glacier's base is wet or dry, include quarrying/plucking and fluvial erosion. We also consider new erosional processes (to be described in this presentation) which are unique to the highly insulating character of solid N2 including both phase change induced hydrofracture and geothermally driven basal melt. Until improvements in our knowledge of solid N2's rheology are made available (including its mechanical behavior as a binary/trinary mixture of CH4 and CO), it is difficult to assess with high precision which of the aforementioned erosion mechanisms are responsible for the observed surface etchings. Nevertheless, we consider a model crater surface and examine its erosional development due to flowing N2 glacial ice as built up over time according to N2 deposition rates based on GCM modeling of Pluto's ancient atmosphere. For given erosional mechanism our aim is to determine the permissible ranges of model input parameters (e.g., ice strength, flow rates, grain sizes, quarrying rates, etc.) that best reproduces the observed length scales found on the observed fluted craters. As of the writing of this abstract, both the processes of quarrying and phase change induced hydrofracture appear to be most promising at explaining the fluted crater ridging.
  7. Hanley, J., Grundy, W., Thompson, G., et al., (including Roe, H.), 2017, AGUFM, 2017, P13D-2590, Methane, Ethane, and Nitrogen Stability on Titan
    Many outer solar system bodies are likely to have a combination of methane, ethane and nitrogen. In particular the lakes of Titan are known to consist of these species. Understanding the past and current stability of these lakes requires characterizing the interactions of methane and ethane, along with nitrogen, as both liquids and ices. Our cryogenic laboratory setup allows us to explore ices down to 30 K through imaging, and transmission and Raman spectroscopy. Our recent work has shown that although methane and ethane have similar freezing points, when mixed they can remain liquid down to 72 K. Concurrently with the freezing point measurements we acquire transmission or Raman spectra of these mixtures to understand how the structural features change with concentration and temperature. Any mixing of these two species together will depress the freezing point of the lake below Titan's surface temperature, preventing them from freezing. We will present new results utilizing our recently acquired Raman spectrometer that allow us to explore both the liquid and solid phases of the ternary system of methane, ethane and nitrogen. In particular we will explore the effect of nitrogen on the eutectic of the methane-ethane system. At high pressure we find that the ternary creates two separate liquid phases. Through spectroscopy we determined the bottom layer to be nitrogen rich, and the top layer to be ethane rich. Identifying the eutectic, as well as understanding the liquidus and solidus points of combinations of these species, has implications for not only the lakes on the surface of Titan, but also for the evaporation/condensation/cloud cycle in the atmosphere, as well as the stability of these species on other outer solar system bodies. These results will help interpretation of future observational data, and guide current theoretical models.
  8. Young, L., Gladstone, R., Summers, M., et al., (including Grundy, W.), 2017, AGUFM, 2017, P13F-02, Pluto's surface composition and atmosphere
    New Horizons studied Pluto's N2-dominated neutral atmosphere through radio (at 4.2 cm with the REX radio experiment), solar and stellar occultations and airglow (at 52-187 nm with the Alice ultraviolet spectrograph), and imaging (with the LORRI and MVIC visible-wavelength cameras). It studied the plasma environment and solar wind interaction with in situ instruments (PEPPSI and SWAP). Contemporaneous observations of Pluto's atmosphere from Earth included a ground-based stellar occultation and ALMA observations of gaseous CO and HCN. Joint analysis of these datasets reveal a variable boundary layer; a stable lower atmosphere; radiative heating and cooling; haze production and hydrocarbon chemistry; diffusive equilibrium; and slower-than-expected escape. New Horizons studied Pluto's surface composition with the LEISA near-infrared spectral imager from 1.25 to 2.5 micron. Additional compositional information at higher spatial resolution came from the MVIC 4-channel color imager, which included a channel centered at 0.89 micron specifically designed to detect solid CH4. These instruments allow mapping of the volatiles N2, CO, and CH4, the surface expression of the H2O bedrock, and the dark, reddish material presumed to be tholins. These observations reveal a large equatorial basin (informally named Sptunik Planitia), filled with N2 ice with minor amounts of CO and CH4, surrounded by hills of CH4 and H2O ice. Broadly speaking, composition outside of Sptunik Planitia follows latitudinal banding, with dark, mainly volatile free terrains near the equator, with N2, CO, and CH4 at mid-northern latitudes, and mainly CH4 at high northern latitudes. Deviations from these broad trends are seen, and point to complex surface-atmosphere interactions at diurnal, seasonal, perennial, and million-year timescales.
  9. Olkin, C., Spencer, J., Grundy, W., et al., 2017, AGUFM, 2017, P13F-03, The Color of Pluto from New Horizons
    The New Horizons flyby provided the first high-resolution color maps of Pluto. These maps show the color variegation across the surface from the very red terrain in the equatorial region, to the more neutral colors of the volatile ices in Sputnik Planitia, the blue terrain of east Tombaugh Regio and the yellow hue on Pluto's north pole. There are two distinct color mixing lines in the color-color diagrams derived from images of Pluto. Both mixing lines have an apparent starting point in common: the relatively neutral color volatile-ice covered terrain. One line extends to the dark red terrain exemplified by Cthulu Regio and the other extends to the yellow hue in the northern latitudes. The red color is consistent with a non-ice component on the surface and is consistent with tholins.
  10. Singer, K., Schenk, P., White, O., et al., (including Grundy, W.), 2017, AGUFM, 2017, P13F-05, Cryovolcanic Resurfacing on Pluto
    Pluto displays several different young geologic terrains with few-to-no identifiable impact craters. Distinct terrains to the southwest of the informally named Sputnik Planitia may have been resurfaced by cryovolcanic processes, of a type and scale so far unique to Pluto [1,2]. The most prominent structures are two very large mounds with deep central depressions. The informally named Wright Mons stands 4 km high and the main mound spans 150 km and Piccard Mons is 7 km high and 225 km wide. Hummocky terrain with a characteristic wavelength of 8-12 km covers the flanks of Wright Mons and much of the surrounding terrain. Smaller boulders, blocks, slabs, or ridges on the order of a few km are superimposed on the hummocks. The large-scale slopes across the broad flanks of the Wright Mons are 3-5. The central depression walls are typically 10, but reach 20 in some locations. A number of other cavi or irregular depressions of various sizes (a few to 30 km) are scattered throughout the terrain and do not appear to be impact craters. There are few signs of potential individual flows but the large-scale hummocky texture is suggestive of viscous flow. We will explore a number of potential mechanisms for creation of Wright and Piccard Mons and the nearby terrains. These unique terrains present modeling challenges for building relatively young, large cryovolcanic constructs on outer solar system bodies. Tidal heating is thought to end early in Pluto-system history [3] and radiogenic heating levels are relatively low [4], although a subsurface ocean may still persist into the present day [5]. We will discuss the possible volcanic materials on Pluto and their mobility under different heating scenarios, as well as other possible emplacement processes. [1] Moore et al., (2016) Science 351, 1284-1293. [2] Singer et al. (2016) LPSC absract 47, 2276. [3] Cheng et al. (2014) Icarus 233, 242-258. [4] McKinnon et al. (1997) In: Stern, S.A., Tholen, D.J. (Eds.), Pluto and Charon. UofA Press, 295-343. [5] Robuchon and Nimmo (2011) Icarus 216, 426-439.
  11. Weaver, H., Buie, M., Howett, C., et al., (including Grundy, W.), 2017, AGUFM, 2017, P13F-06, Small Bodies in the Kuiper Belt : Lessons from Pluto's Small Satellites
    During the approach and flyby of the Pluto system in 2015, the instruments on theNew Horizons spacecraft obtained data on Pluto's small satellites that far surpassedwhat was previously available. All four small moons (Styx, Nix, Kerberos, and Hydra,in order of distance from Pluto) have highly irregular shapes, rapid non-synchronous rotation rates, high obliquity rotational poles, high visible albedos ( 50-80%), andneutral-to-blue visible colors. The even more detailed information obtained for Nix and Hydra reveal those 40 km diameter objects to have relatively ancient ( 3-4 Gyr) surfacesdominated by crystalline water ice, but with a hint of ammonia-containing compounds. Here we addresswhat these results say about the origin and evolution of these bodies, and howthese results inform studies of other small bodies in the Kuiper belt, including2014 MU69, the next flyby target for the New Horizons mission.
  12. Buie, M., Porter, S., Terrell, D., et al., (including Wasserman, L.), 2017, AGUFM, 2017, P13F-08, A Preview of 2014MU69 Revealed by HST and a Ground-based Stellar Occultation
    The upcoming encounter of New Horizons with (486985) 2014MU69 will be an important and rare opportunity for close-up study of a cold-classical Kuiper Belt object. In preparation for this encounter we have been trying to learn more to aid in planning for this upcoming event. A considerable time has been spent with the Hubble Space Telescope making astrometric and photometric observations. When combined with the ESA Gaia mission data, we now have a very good orbit estimate that will be used to support navigation of New Horizons to its encounter but also good enough to accurately predict stellar occultation observations. In 2017, we pursued three stellar occultation opportunities. The first event was on 2017 June 3 and predicted to be visible from southern South America and southern Africa with a somewhat faint star with g'=15.33. The second event was on 2017 June 10 under very difficult observing conditions just 16 from a full moon and the faintest star of the three with g'=15.57. The third event was on 2017 July 17 and predicted to be visible from southern Argentina with the brightest star of the three with g'=12.60. The second event was on 2017 June 10 under very difficult observing conditions just 16 from a full moon and the faintest star of the three with g'=15.57. The third event was on 2017 July 17 and predicted to be visible from southern Argentina with the brightest star of the three with g'=12.60. The first and third events were amenable to a ground-based telescope deployment and we fielded 25 telescopes. The second event was possible only with SOFIA (Stratospheric Observatory For Infrared Astronomy). All campaigns were successful in recording data essential for the constraint on dust or rings around MU69: June 3, 24 lightcurves; July 10, 1 lightcurve; July 17, 23 lightcurves. Only the last event was able to record solid-body chords from the object with 5 chords detected close to the predicted time and place. We will present the results and implications of these occultation observations as well as a summary of the other physical observations collected so far from HST and provide the context for the upcoming New Horizons encounter.
  13. Moore, J., Grundy, W., Spencer, J., et al., 2017, AGUFM, 2017, P13F-09, Great Expectations: The New Horizons Imaging and Composition Pre-Encounter Plans and Contemplations of 2014 MU69
    The New Horizons encounter with 2014 MU69 on 1 January 2019 will be the first small Kuiper belt object to be studied in detail from a spacecraft. The prospect that the cold classical population, which includes 2014 MU69, may represent a primordial, in situ population is exciting. Indeed, as we have learned just how complex and dynamic the early Solar System was, the cold classical population of the Kuiper belt has emerged as a singular candidate for a fundamentally unaltered original planetesimal population. MU69 in particular provides 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 in 4 channels at 0.4 to 1 at 200 - 500 m/pixel, and 256 channel spectroscopy from 1.25 to 2.5 at 1 - 4 km/pixel. Ices such as H2O, NH3, CO2, and CH3OH would be stable and can be detected and mapped if they are exposed at the surface. It will be especially instructive to compare with Cassini VIMS spectra of Phoebe, thought to be a captured outer solar system planetesimal that formed in a related nebular environment to where MU69 formed.
  14. Johnson, J., Bell, J., Hayes, A., et al., (including Grundy, W.), 2017, AGUFM, 2017, P31A-2794, Modeling of Mastcam Visible/Near-Infrared Spectrophotometric Observations at Yellowknife Bay
    The Mastcam M-34 imaging system on the Curiosity rover has acquired multispectral images (445, 527, 751, 1012 nm) at multiple times of day at several locations along the traverse, sampling a variety of terrain types [1-4]. The light scattering properties of rocks and soils can be examined quantitatively using radiative transfer models with data extracted from these images [5-7], with the goals of providing information useful for understanding microphysical processes, atmospheric models, and orbital observations. Navcam stereo images also were acquired to compute surface normals and local incidence and emission angles. These can be combined with sky models to correct for diffuse reflectance on individual surface facets prior to photometric modeling. Here we model data sets acquired on Sols 171-184 while the rover was parked at the John Klein drill site in Yellowknife Bay [2]. Regions of interest were extracted from M-34 images on soils, rocks with variable dust cover, and rover tracks to provide data sets with sufficient phase angle coverage to allow Hapke radiative transfer modeling of each unit. Preliminary model results performed without the atmospheric correction showed rover tracks exhibited 1-term Henyey-Greenstein (HG) asymmetry parameter values consistent with more forward scattering surfaces compared to rocks. The 2-term HG scattering parameters (b and c) suggested that soils and dusty rocks were more backscattering than less dusty rocks, consistent with results from the MER Spirit site [5]. Preliminary single-scattering albedo values for soils varied from 0.38 (445 nm) to 0.87 (1012 nm); less dusty rocks varied from 0.59 (445 nm) to 0.81 (1012 nm). Macroscopic roughness values showed larger values for less dusty rocks (17-22). Opposition effect width (h) values implied higher porosity (or less uniform grain size distributions) in rocks than soils. Model results presented at the meeting will incorporate sky models. Future work will include additional Mastcam data sets. [1] Johnson, J., et al., LPSC, 44, abstract #1374, 2013;[2] Johnson, J., et al. 8th Int. Conf. Mars, #1073, 2014; [3] Johnson, J., et al., LPSC, #1424, 2015; [4] Johnson, J., et al., AGU, #P43B-2125 2015; [5] Johnson, J., et al., JGR, 111, E02S14, 2006; [6] Johnson, J., et al. JGR, 111, E12S16, 2006; [7] Johnson, J. et al., Icarus, 248, 25-71, 2015.
  15. Liang, W., Johnson, J., Hayes, A., et al., (including Grundy, W.), 2017, AGUFM, 2017, P31A-2795, Spectrophotometric Modeling of MAHLI Goniometer Observations
    The Mars Hand Lends Imager (MAHLI) on the Curiosity rover's robotic arm was used as a goniometer to acquire a multiple-viewpoint data set on sol 544 [1]. Images were acquired at 20 arm positions, all centered at the same location and from a near-constant distance of 1.0 m from the surface. Although this sequence was acquired at only one time of day ( 13:30 LTST), it provided phase angle coverage from 0-110. Images were converted to radiance from calibrated PDS files (DRXX) using radiance scaling factors and MAHLI focus position counts in an algorithm that rescaled the data to match the Mastcam M-34 calibration via comparison of sky images acquired during the mission. Converted MAHLI radiance values from an image of the Mastcam calibration target compared favorably in the red, green, and blue Bayer filters to M-34 radiance values from an image of the same target taken minutes afterwards. The 20 MAHLI images allowed construction of a digital terrain model (DTM), although images with shadows cast by the rover arm were more challenging to include. Their current absence restricts the lowest phase angles available to about 17. The DTM enables calculation of surface normals that can be used with sky models to correct for diffuse reflectance on surface facets prior to Hapke modeling [cf. 2-6]. Regions of interest (ROIs) were extracted using one of the low emission-angle images as a template. ROI unit types included soils, light-toned surfaces (5 cm felsic rock "Nita"), dark-toned rocks with variable textures and dust cover, and larger areas representative of the average surface (see attached figure). These ROIs were translated from the template image to the other images through a matching of DTM three-dimensional coordinates. Preliminary phase curves (prior to atmospheric correction) show that soil-dominated surfaces are most backscattering, whereas rocks are least backscattering, and light-toned surfaces exhibit wavelength-dependent scattering. Future work will include all images in the DTM and incorporate sky models to correct for diffuse skylight. [1] Johnson, J., et al. 8th Int. Conf. Mars, #1073, 2014; [2] Johnson, J., et al., LPSC, #1424, 2015; [3] Johnson, J., et al., AGU, #P43B-2125 2015; [4] Johnson, J., et al., JGR, 111, E02S14, 2006; [5] Johnson, J., JGR, 111, E12S16, 2006; [6] Johnson,J. et al., Icarus, 248, 25-71, 2015.
  16. Spencer, J., Grundy, W., 2017, AGUFM, 2017, P43D-2907, The Longitudinal Distribution of Condensed Oxygen on Europa
    Condensed oxygen is likely to play an important role in the complex chemical environment of the surfaces of the icy Galilean satellites, being important in a radiolytic cycle that includes O3 and H2O2, and which may provide significant chemical energy to the subsurface ocean on Europa. O2 has been identified on Ganymede (Spencer et al. 1995), and subsequently on Europa and Callisto (Spencer and Calvin 2002) by means of its shallow but distinctive 5773 and 6250 A absorption bands. 5773 A band strength is up to 2% on Ganymede, but only 0.3% on Europa. O2 on Ganymede exhibits a strong concentration on the trailing hemisphere, suggesting a magnetospheric origin, but the distribution on Europa has been poorly known due to the extreme weakness of the absorption band. We report on new high SNR spectroscopy of the O2 band on Europa, obtained on eight partial nights in June 2017 using the DeVeny Spectrograph on the 4.3-m Lowell Discovery Channel Telescope. The improved SNR of the new data provides the first good constraints on the longitudinal distribution of O2 on Europa, which may provide clues to the origin and evolution of this species.
  17. Raiteri, C., Villata, M., Acosta-Pulido, J., et al., (including Skiff, B.), 2017, Natur, 552, 374, Blazar spectral variability as explained by a twisted inhomogeneous jet
    Blazars are active galactic nuclei, which are powerful sources of radiation whose central engine is located in the core of the host galaxy. Blazar emission is dominated by non-thermal radiation from a jet that moves relativistically towards us, and therefore undergoes Doppler beaming. This beaming causes flux enhancement and contraction of the variability timescales, so that most blazars appear as luminous sources characterized by noticeable and fast changes in brightness at all frequencies. The mechanism that produces this unpredictable variability is under debate, but proposed mechanisms include injection, acceleration and cooling of particles, with possible intervention of shock waves or turbulence. Changes in the viewing angle of the observed emitting knots or jet regions have also been suggested as an explanation of flaring events and can also explain specific properties of blazar emission, such as intra-day variability, quasi-periodicity and the delay of radio flux variations relative to optical changes. Such a geometric interpretation, however, is not universally accepted because alternative explanations based on changes in physical conditionssuch as the size and speed of the emitting zone, the magnetic field, the number of emitting particles and their energy distributioncan explain snapshots of the spectral behaviour of blazars in many cases. Here we report the results of optical-to-radio-wavelength monitoring of the blazar CTA 102 and show that the observed long-term trends of the flux and spectral variability are best explained by an inhomogeneous, curved jet that undergoes changes in orientation over time. We propose that magnetohydrodynamic instabilities or rotation of the twisted jet cause different jet regions to change their orientation and hence their relative Doppler factors. In particular, the extreme optical outburst of 2016-2017 (brightness increase of six magnitudes) occurred when the corresponding emitting region had a small viewing angle. The agreement between observations and theoretical predictions can be seen as further validation of the relativistic beaming theory.
  18. Angerhausen, D., Dreyer, C., Placek, B., et al., (including Collins, P., Dunham, E., Mandushev, G.), 2017, A&A, 608, A120, Simultaneous multicolour optical and near-IR transit photometry of GJ 1214b with SOFIA
    Context. The benchmark exoplanet GJ 1214b is one of the best studied transiting planets in the transition zone between rocky Earth-sized planets and gas or ice giants. This class of super-Earth or mini-Neptune planets is unknown in our solar system, yet is one of the most frequently detected classes of exoplanets. Understanding the transition from rocky to gaseous planets is a crucial step in the exploration of extrasolar planetary systems, in particular with regard to the potential habitability of this class of planets.
    Aims: GJ 1214b has already been studied in detail from various platforms at many different wavelengths. Our airborne observations with the Stratospheric Observatory for Infrared Astronomy (SOFIA) add information in the Paschen- cont. 1.9 m infrared wavelength band, which is not accessible by any other current ground- or space-based instrument due to telluric absorption or limited spectral coverage.
    Methods: We used FLIPO, the combination of the High-speed Imaging Photometer for Occultations (HIPO) and the First Light Infrared TEst CAMera (FLITECAM) and the Focal Plane Imager (FPI+) on SOFIA to comprehensively analyse the transmission signal of the possible water-world GJ 1214b through photometric observations during transit in three optical and one infrared channels.
    Results: We present four simultaneous light curves and corresponding transit depths in three optical and one infrared channel, which we compare to previous observations and current synthetic atmospheric models of GJ 1214b. The final precision in transit depth is between 1.5 and 2.5 times the theoretical photon noise limit, not sensitive enough to constrain the theoretical models any better than previous observations. This is the first exoplanet observation with SOFIA that uses its full set of instruments available to exoplanet spectrophotometry. Therefore we use these results to evaluate SOFIA's potential in this field and suggest future improvements.

    Tables of the lightcurve data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/608/A120

  19. Eisner, N., Knight, M., Schleicher, D., 2017, AJ, 154, 196, The Rotation and Other Properties of Comet 49P/Arend-Rigaux, 1984-2012
    We analyzed images of comet 49P/Arend-Rigaux on 33 nights between 2012 January and May and obtained R-band lightcurves of the nucleus. Through usual phasing of the data, we found a double-peaked lightcurve having a synodic rotation period of 13.450 0.005 hr. Similarly, phase dispersion minimization and the Lomb-Scargle method both revealed rotation periods of 13.452 hr. Throughout the 2011/2012 apparition, the rotation period was found to increase by a small amount, consistent with a retrograde rotation of the nucleus. We also reanalyzed the publicly available data from the 1984/1985 apparition by applying the same techniques, finding a rotation period of 13.45 0.01 hr. Based on these findings, we show that the change in rotation period is less than 14 s per apparition. Furthermore, the amplitudes of the lightcurves from the two apparitions are comparable, to within reasonable errors, even though the viewing geometries differ, implying that we are seeing the comet at a similar sub-Earth latitude. We detected the presence of a short-term jet-like feature in 2012 March, which appears to have been created by a short-duration burst of activity on March 15. Production rates obtained in 2004/2005, along with reanalysis of the previous results from 1984/1985, imply a strong seasonal effect and a very steep fall-off after perihelion. This, in turn, implies that a single source region, rather than leakage from the entire nucleus, dominates activity.
  20. Polishook, D., Moskovitz, N., Thirouin, A., et al., (including Levine, S.), 2017, Icar, 297, 126, The fast spin of near-Earth asteroid (455213) 2001 OE84, revisited after 14 years: Constraints on internal structure
    At a mean diameter of 650 m, the near-Earth asteroid (455213) 2001 OE84 (OE84 for short) has a rapid rotation period of 0.486542 0.000002 h, which is uncommon for asteroids larger than 200 m. We revisited OE84 14 years after it was first, and last, observed by Pravec et al. (2002) in order to measure again its spin rate and to search for changes. We have confirmed the rapid rotation and, by fitting the photometric data from 2001 and 2016 using the lightcurve inversion technique, we determined a retrograde sense of rotation, with the spin axis close to the ecliptic south pole; an oblate shape model of a / b = 1.32 0.04 and b / c = 1.8 0.2 ; and no change in spin rate between 2001 and 2016. Using these parameters we constrained the body's internal strength, and found that current estimations of asteroid cohesion (up to 80 Pa) are insufficient to maintain an intact rubble pile at the measured spin rate of OE84. Therefore, we argue that a monolithic asteroid, that can rotate at the rate of OE84 without shedding mass and without slowing down its spin rate, is the most plausible for OE84, and we give constraints on its age, since the time it was liberated from its parent body, between 2 - 10 million years.
  21. Pasachoff, J., Babcock, B., Durst, R., et al., (including Levine, S., Bosh, A.), 2017, Icar, 296, 305, Pluto occultation on 2015 June 29 UTC with central flash and atmospheric spikes just before the New Horizons flyby
    We observed the occultation by Pluto of a 12th magnitude star, one of the two brightest occultation stars ever in our dozen years of continual monitoring of Pluto's atmosphere through such studies, on 2015 June 29 UTC. At the Univ. of Canterbury Mt. John Observatory (New Zealand), under clear skies throughout, we used a POETS frame-transfer CCD at 10 Hz with GPS timing on the 1-m McLellan telescope as well as an infrared camera on an 0.6-m telescope and three-color photometry at a slower cadence on a second 0.6-m telescope. At the Auckland Observatory, we used a POETS and a PICO on 0.5-m and 0.4-m telescopes, with 0.4 s and 2 s cadences, respectively, obtaining ingress observations before clouds moved in. The Mt. John light curves show a central flash, indicating that we were close to the center of the occultation path. Analysis of our light curves show that Pluto's atmosphere remains robust. The presence of spikes at both sites in the egress and ingress shows atmospheric layering. We coordinated our observations with aircraft observations (Bosh et al., 2017) with the Stratospheric Observatory for Infrared Astronomy (SOFIA). Our chords helped constrain the path across Pluto that SOFIA saw. Our ground-based and airborne stellar-occultation effort came only just over two weeks of Earth days and two Pluto days before the flyby of NASA's New Horizons spacecraft.
  22. Massey, P., Levesque, E., Neugent, K., et al., (including Evans, K.), 2017, IAUS, 329, 161, The Red Supergiant Content of the Local Group
    We summarize here recent work in identifying and characterizing red supergiants (RSGs) in the galaxies of the Local Group.
  23. Neugent, K., Massey, P., Hillier, D., et al., 2017, IAUS, 329, 176, The Evolutionary Status of WN3/O3 Wolf-Rayet Stars
    As part of a multi-year survey for Wolf-Rayet stars in the Magellanic Clouds, we have discovered a new type of Wolf-Rayet star with both strong emission and absorption. While one might initially classify these stars as WN3+O3V binaries based on their spectra, such a pairing is unlikely given their faint visual magnitudes. Spectral modeling suggests effective temperatures and bolometric luminosities similar to those of other early-type LMC WNs but with mass-loss rates that are three to five times lower than expected. They additionally retain a significant amount of hydrogen, with nitrogen at its CNO-equilibrium value (10 enhanced). Their evolutionary status remains an open question. Here we discuss why these stars did not evolve through quasi-homogeneous evolution. Instead we suggest that based on a link with long-duration gamma ray bursts, they may form in lower metallicity environments. A new survey in M33, which has a large metallicity gradient, is underway.
  24. Leith, T., Moskovitz, N., Mayne, R., et al., (including Burt, B.), 2017, Icar, 295, 61, The compositional diversity of non-Vesta basaltic asteroids
    We present near-infrared (0.78-2.45 m) reflectance spectra for nine middle and outer main belt (a > 2.5 AU) basaltic asteroids. Three of these objects are spectrally distinct from all classifications in the Bus-DeMeo system and could represent spectral end members in the existing taxonomy or be representatives of a new spectral type. The remainder of the sample are classified as V- or R-type. All of these asteroids are dynamically detached from the Vesta collisional family, but are too small to be intact differentiated parent bodies, implying that they originated from differentiated planetesimals which have since been destroyed or ejected from the solar system. The 1- and 2-m band centers of all objects, determined using the Modified Gaussian Model (MGM), were compared to those of 47 Vestoids and fifteen HED meteorites of known composition. The HEDs enabled us to determine formulas relating Band 1 and Band 2 centers to pyroxene ferrosilite (Fs) compositions. Using these formulas we present the most comprehensive compositional analysis to date of middle and outer belt basaltic asteroids. We also conduct a careful error analysis of the MGM-derived band centers for implementation in future analyses. The six outer belt V- and R-type asteroids show more dispersion in parameter space than the Vestoids, reflecting greater compositional diversity than Vesta and its associated bodies. The objects analyzed have Fs numbers which are, on average, between five and ten molar percent lower than those of the Vestoids; however, identification and compositional analysis of additional outer belt basaltic asteroids would help to confirm or refute this result. Given the gradient in oxidation state which existed within the solar nebula, these results tentatively suggest that these objects formed at either a different time or location than 4 Vesta.
  25. De Marco, O., Reichardt, T., Iaconi, R., et al., (including Jacoby, G.), 2017, IAUS, 323, 213, Post-common envelope PN, fundamental or irrelevant?
    One in 5 PN are ejected from common envelope binary interactions but Kepler results are already showing this proportion to be larger. Their properties, such as abundances can be starkly different from those of the general population, so they should be considered separately when using PN as chemical or population probes. Unfortunately post-common envelope PN cannot be discerned using only their morphologies, but this will change once we couple our new common envelope simulations with PN formation models.
  26. Nicholl, M., Berger, E., Kasen, D., et al., (including Moskowitz, N.), 2017, ApJL, 848, L18, The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. III. Optical and UV Spectra of a Blue Kilonova from Fast Polar Ejecta
    We present optical and ultraviolet spectra of the first electromagnetic counterpart to a gravitational-wave (GW) source, the binary neutron star merger GW170817. Spectra were obtained nightly between 1.5 and 9.5 days post-merger, using the Southern Astrophysical Research and Magellan telescopes; the UV spectrum was obtained with the Hubble Space Telescope at 5.5 days. Our data reveal a rapidly fading blue component (T 5500 K at 1.5 days) that quickly reddens; spectra later than 4.5 days peak beyond the optical regime. The spectra are mostly featureless, although we identify a possible weak emission line at 7900 A at t 4.5 days. The colors, rapid evolution, and featureless spectrum are consistent with a blue kilonova from polar ejecta comprised mainly of light r-process nuclei with atomic mass number A 140. This indicates a sightline within { }{obs} 45^\circ of the orbital axis. Comparison to models suggests 0.03 M of blue ejecta, with a velocity of 0.3c. The required lanthanide fraction is {10}-4, but this drops to < {10}-5 in the outermost ejecta. The large velocities point to a dynamical origin, rather than a disk wind, for this blue component, suggesting that both binary constituents are neutron stars (as opposed to a binary consisting of a neutron star and a black hole). For dynamical ejecta, the high mass favors a small neutron star radius of 12 km. This mass also supports the idea that neutron star mergers are a major contributor to r-process nucleosynthesis.
  27. Radebaugh, J., Telfer, M., Parteli, E., et al., (including Grundy, W.), 2017, DPS, 49, 102.05, Dunes as New Evidence of Recently Active Surface Processes on Pluto
    The surface of Pluto contains hundreds of aligned, regularly spaced features best described as transverse dunes (Telfer et al. in review). They are spaced by 500-700 meters, are several tens of kilometers long, and are subparallel and with a slightly undulatory planform, as seen by the New Horizons LORRI instrument. Their crests are orthogonal to wind streaks seen nearby, and therefore to the assumed regional winds. They sit atop the nitrogen-rich informally named Sputnik Planitia continental glacier at the base of the informally named Al-Idrisi Montes and appear from New Horizons MVIC data to have a composition enriched in methane. Their presence requires there to be particles that can be saltated as well as wind. The particles, or sands, are likely composed of relatively hard methane ice, possibly derived from the methane snow seen to blanket the mountain summits. While Plutos nitrogen-rich atmosphere fluctuates in density, perhaps dramatically, current modelled conditions allow for winds that are required to saltate the ice sands (<~10 m/s). These features are relatively fresh in appearance, especially in comparison with features farther south that have severe sublimation erosion textures and deformation from glacier flow. Furthermore, they lie atop convection cell margins of Sputnik Planitia, which overturns at rates of ~500 ka. This indicates the dune-like landforms of Pluto are relatively young. This has implications for the surface activity of other large Kuiper Belt Objects and the interaction between limited solar heating and the exotic properties of their surfaces and atmospheres.
  28. Cruikshank, D., Spohrer, S., Grundy, W., et al., 2017, DPS, 49, 102.06, Pluto: Fluidized transport of tholins by heating of the subsurface
    New Horizons images of Pluto show evidence of the transport of the colored non-ice component across the surface, with substantial accumulations in some areas of low elevation. The non-ice component is presumed to be tholin produced in the atmosphere as a precipitating aerosol, in the surface ices by photolysis or radiolysis, or both. We model the surface layer of N2 ice with varying amounts of incorporated tholin particles to explore the heating within the ice that occurs by the solid-state greenhouse effect. We find that in plausible models of the contaminated N2 surface ice the triple point temperature (63.15K) is reached at a depth of ~< 1m. At that depth the confining pressure of the ice column is much less than the triple point pressure (12.52 kPa), so N2 should convert to the gas phase, exerting pressure on the overburden. When the gas pressure exceeds the strength of the confining ice, a breakout on the surface will occur, fluidizing fragments of ice and its contaminants that are then free to flow downhill, rafted on entrained gas, similar in some ways to the pyroclastic volcanic phenomenon known as nuee ardente. The digital elevation map of Pluto made from stereo images shows some surface regions that may have been stripped of the N2 layer, exposing H2O ice (presumed to be bedrock) below, with a corresponding accumulation of dark material that was that was the previously entrained particulate tholin. Accumulations of tholin are found associated with some of the fossae, and some cover preexisting topography to depths of up to a few hundred meters. Supported by the New Horizons project.
  29. Dalle Ore, C., Protopapa, S., Cruikshank, D., et al., (including Grundy, W.), 2017, DPS, 49, 102.07, Plutos non-icy component: a close-in analysis
    The understanding of the origin and evolution of Pluto, and, by extension, that of a vast number of similar sized and smaller bodies in the Third Zone of the solar system, are closely tied to their atmosphere and surface chemistry. In turn, a major role in the composition and coloration (from dark red to yellow) of the surface -and indirectly the atmosphere- of Pluto is played by non-ice components presumed to be organic compounds known as tholins. While some of these compounds have been reproduced in the laboratory by irradiation of native materials found in Plutos atmosphere and surface, the number of kinds of tholins on the surface of Pluto, and the processes responsible for their formation and distribution is still subject of investigation. We make use of Pluto data from the New Horizons Ralph instrument consisting of a multicolor/panchromatic mapper (MVIC) and mapping infrared (IR) composition spectrometer (LEISA). For this study we have adopted a set of scans at high spatial resolution (on average 2.7 km/pixel), spectroscopically analyzed for the first time. Our preliminary analysis shows different signatures for the dark red material that could be attributed to either grain size or composition/nature of the darkening agent. We characterize and inter-compare the potentially different tholins aiming at understanding its/their history and chemical evolution.
  30. Umurhan, O., Howard, A., White, O., et al., (including Grundy, W.), 2017, DPS, 49, 102.08, Pluto's Paleoglaciation: Processes and Bounds
    New Horizons imaging of Plutos surface shows eroded landscapes reminiscent of assorted glaciated terrains found on the Earth such as alpine valleys, dendritic networks and others. For example, LORRI imaging of fluted craters show radially oriented ridging which also resembles Plutos washboard terrain. Digital elevation modeling indicates that these down-gradient oriented ridges are about 3-4 km spaced apart with depths ranging from 0.2-0.5 km. Present day glaciation on Pluto is characterized by moving N2 ice blocks presumably riding over a H2O ice bedrock substrate. Assuming Plutos ancient surface was sculpted by N2 glaciation, what remains a mystery is the specific nature of the glacial erosion mechanism(s) responsible for the observed features.To better resolve this puzzle, we perform landform evolution modeling of several glacial erosion processes known from terrestrial H2O ice glaciation studies. These terrestrial processes, which depend upon whether or not the glaciers base is wet or dry, include quarrying/plucking and fluvial erosion. We also consider new erosional processes (to be described in this presentation) which are unique to the highly insulating character of solid N2 including both phase change induced hydrofracture and geothermally driven basal melt. Until improvements in our knowledge of solid N2s rheology are made available (including its mechanical behavior as a binary/trinary mixture of CH4 and CO), it is difficult to assess with high precision which of the aforementioned erosion mechanisms are responsible for the observed surface etchings.Nevertheless, we consider a model crater surface and examine its erosional development due to flowing N2 glacial ice as built up over time according to N2 deposition rates based on GCM modeling of Plutos ancient atmosphere. For given erosional mechanism our aim is to determine the permissible ranges of model input parameters (e.g., ice strength, flow rates, grain sizes, quarrying rates, etc.) that best reproduces the observed length scales found on the observed fluted craters. As of the writing of this abstract, both the processes of quarrying and phase change induced hydrofracture appear to be most promising at explaining the fluted crater ridging.
  31. Earle, A., Grundy, W., Howett, C., et al., 2017, DPS, 49, 102.09, Methane Distribution on Pluto as Mapped by New Horizons' Ralph/MVIC Instrument
    The data returned from NASAs 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. 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 Plutos surface. From these maps we can then quantitatively study the relationships between methane distribution, redness, and other parameters like latitude and altitude. In this talk, we will look at these relationships and how they improve our understanding of Plutos geology and serves as a guide for refining volatile transport models.
  32. Le Corre, L., Reddy, V., Sanchez, J., et al., (including Thirouin, A.), 2017, DPS, 49, 110.05, Ground-based Characterization of Hayabusa2 Mission Target Asteroid 162173 Ryugu
    In preparation for the arrival of the Japanese Space Agencys (JAXA) Hayabusa2 sample return mission to near-Earth asteroid (NEA) (162173) Ryugu, we took the opportunity to characterize the target with a ground-based telescope. We observed Ryugu using the SpeX instrument in Prism mode on NASA Infrared Telescope Facility on Mauna Kea, Hawaii, on July, 12 2016 when the asteroid was 18.87 visual magnitude, at a phase angle of 13.3. The NIR spectra were used to constrain Ryugus surface composition, meteorite analogs and spectral affinity to other asteroids. We also modeled 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 Masateru et al. (2014). Our spectrum of Ryugu has a broad absorption band at 1 m, a slope change at 1.6 m, and a second broad absorption band near 2.2 m, but no well-defined absorption features over the 0.8-2.5 m range. The two broad absorption features, if confirmed, are consistent with CO and CV chondrites. The shape of Ryugus spectrum matches very well those of NEA (85275) 1994 LY and Mars-crossing asteroid (316720) 1998 BE7, suggesting that their surface regolith have similar composition. We also compared the spectrum of Ryugu with that of main belt asteroid (302) Clarissa, the largest asteroid in the Clarissa asteroid family, suggested as the source of Ryugu by Campins et al. (2013). We found that the spectrum of Clarissa shows significant differences with our NIR spectrum of Ryugu. Our analysis shows Ryugus spectrum best matches two CM2 carbonaceous chondrites, Mighei and ALH83100. We expect the surface regolith of Ryugu to be altered by a range of factors including temperature, contamination by exogenic material, and space weathering, posing challenges to link spacecraft and ground-based data, and sample site selection.
  33. Polishook, D., Moskovitz, N., Benecchi, S., et al., 2017, DPS, 49, 110.24, A HST campaign to search for widely separated satellites around asteroid pairs
    An unbound asteroid pair is formed by the rotational disruption of an asteroid resulting in the ejection of a secondary body. Since some bound satellites (binary asteroids) are considered to form by the same mechanism, it has been suggested that the two populations may be linked. Indeed, photometric observations found a few asteroid pairs each with a bound satellite, suggesting the disruption resulted in multiple ejected components. The disruptions into multiple components of P/2013 R3 and P/2012 F5, observed by the Hubble Space Telescope (HST), support this scenario and raise the question of the likelihood that rotationally disrupted asteroid having both bound and lost components. Specifically, since the events of P/2013 R3 and P/2012 F5 resulted in ejecta at high separation, high resolution observations could reveal unknown satellites in a parameter-space not measureable by typical ground-based photometry. 3749 Balam, which has an unbound secondary, a near-by satellite and a widely separated satellite, is an example of such a complex, multi-component system.We performed a pilot campaign using WFC3 on the HST to search for widely separated satellites (>20 asteroid radii) orbiting the primary members of six asteroid pairs. Since the signal from the asteroid is not completely removed by subtraction, our algorithm is sensitive to signals from satellites outside a 2-pixel radius from the asteroid center on the image. We tested the sensitivity of our algorithm with 30 synthetic satellites added to the images inside of the Hill sphere of the asteroids, and found a detection success rate of ~95%.We did not find a clear satellite signal in the images for any of the six asteroid pair primaries. Using the synthetic satellites, we determined an inverse correlation of the minimal distance from the asteroid in which a satellite would be detected as a function of the diameter ratio of the satellite relative to the asteroid. Since the parameters of known asteroids with widely separated satellites place them away from our minimal detection limit, we conclude that the observed asteroid pairs do not have widely separated satellites. Thus 3749 Balam appears to be a unique case within the group of asteroid pairs.
  34. Thomas, C., Moskovitz, N., Lim, L., et al., 2017, DPS, 49, 110.25, Searching for a Differentiated Asteroid Family: A Spectral Survey of the Massalia, Merxia, and Agnia Families
    Asteroid families were formed by catastrophic collisions or large cratering events that caused fragmentation of the parent body and ejection of asteroidal fragments with velocities sufficient to prevent re-accretion. Due to these formation processes, asteroid families provide us with the opportunity to probe the interiors of the former parent bodies. Differentiation of a large initially chondritic parent body is expected to result in an onion shell" object with an iron-nickel core, a thick olivine-dominated mantle, and a thin plagioclase/pyroxene crust. However, most asteroid families tend to show similar spectra (and therefore composition) among the members. Spectroscopic studies have observed a paucity of metal-like materials and olivine-dominated assemblages within Main Belt asteroid families.The deficit of olivine-rich mantle material in the meteorite record and in asteroid observations is known as the Missing Mantle" problem. For years the best explanation has been the battered to bits" hypothesis: differentiated parent bodies (aside from Vesta) were disrupted very early in the Solar System and the olivine-rich material was collisionally broken down over time. Alternatively, Elkins-Tanton et al. (2013) have suggested that previous work has overestimated the amount of olivine produced by the differentiation of a chondritic parent body.We have completed a visible and near-infrared wavelength spectral survey of asteroids in the Massalia, Merxia, and Agnia S-type Main Belt asteroid families. These families were carefully chosen for the spectroscopic survey because they have compositions most closely associated with a history of thermal metamorphism and because they represent a range of collisional formation scenarios. Additionally, members of the Merxia and Agnia families were identified as products of differentiation by Sunshine et al. (2004).Our spectral analyses suggest that the observed families contain products of partial differentiation. We will present results from our spectral survey of these three families and discuss any evidence of differentiation among the family members. We will discuss our band parameter analyses and compositional results from the Modified Gaussian Model (MGM).
  35. Noll, K., Grundy, W., Buie, M., et al., 2017, DPS, 49, 110.40, Resolved Observations of the Patroclus-Menoetius Binary
    The Trojan binary (617) Patroclus-Menoetius is one of the targets of the Lucy Discovery mission. Lucy is scheduled to launch in October 2021. We observed this system with the Hubble Space Telescope in May and June 2017 in order to resolve the individual components and use the relative positions to update the binary orbit. The updated orbit is required to predict the upcoming mutual event season. A precise determination of the orbit phase, period, orbit plane and pole position that will result from observations of mutual events is essential for planning the Lucy missions encounter with this system. We present results of the successful HST observations including preliminary predictions for mutual events observable in semester 2018A.
  36. Benson, C., Scheeres, D., Moskovitz, N., 2017, DPS, 49, 117.05, Asteroid (367943) 2012 DA14 Flyby Spin State Analysis
    On February 15, 2013 asteroid 2012 DA14 experienced an extremely close Earth encounter, passing within 27700 km altitude. This flyby gave observers the chance to directly detect flyby-induced changes to the asteroids spin state and physical properties. The strongest shape and spin state constraints were provided by Goldstone delay-Doppler radar and visible-wavelength photometry taken after closest approach. These data indicated a roughly 40 m x 20 m object in non-principal axis rotation. NPA states are described by two fundamental periods. P is the average precession period of the long/short axis about the angular momentum vector and P is the rotation period about the long/short axis.WindowCLEAN (Belton & Gandhi 1988) power spectrum analysis of the post flyby light curve showed three prominent frequencies, two of which were 1:2 multiples of each other. Mueller et al. (2002) suggest peaks with this relationship are 1/P and 2/P, implying that P = 6.35 hr. Likely values for P were then 8.72, 13.95, or 23.39 hr. These P,P pairs yielded six candidate spin states in total, one LAM and one SAM per pair.Second to fourth order, two-dimensional Fourier series fits to the light curve were best for periods of 6.359 and 8.724 hr. The two other candidate pairs were also in the top ten fits. Inertia constraints of a roughly 2:1 uniform density ellipsoid eliminated two of the three SAM states. Using JPL Horizons ephemerides and Lambertian ellipsoids, simulated light curves were generated. The simulated and observed power spectra were then compared for all angular momentum poles and reasonable ellipsoid elongations. Only the P = 6.359 hr and P = 8.724 hr LAM state produced light curves consistent with the observed frequency structure. All other states were clearly incompatible. With two well-fitting poles found, phasing the initial attitude and angular velocity yielded plausible matches to the observed light curve. Neglecting gravitational torques, neither pole agreed with the observed pre-flyby light curve, suggesting that the asteroids spin state changed during the encounter, consistent with numerical simulation predictions. The consistency between the pre-flyby observations and simulated states will be discussed.
  37. Grundy, W., Umurhan, O., 2017, DPS, 49, 202.02, Are Makemake and Eris Sputnik Planets?
    Makemake and Eris have high albedos (Sicardy et al. 2011; Ortiz et al. 2012) and show strong spectral absorption by CH4 ice (Licandro et al. 2006; Brown et al. 2007; Dumas et al. 2007). Energetic space radiation breaks C-H bonds in CH4 producing fragments that recombine into dark, red macromolecular materials (tholins, e.g., Johnson et al. 1987; Thompson et al. 1987; Strazzulla et al. 1991). This fact, coupled with Pluto's strong CH4 ice absorption bands and high albedo led Stern (1988) to pose the question "why is Pluto bright?". New Horizons has confirmed that Pluto refreshes its surface via seasonal volatile transport (e.g., Stern et al. 2015). However, one part of Pluto refreshes itself in a different way, too. This is the informally named Sputnik Planitia, a vast plain of volatile ice partly filling a probable impact basin. The ice is thick enough to act as a barrier to internal radiogenic heat flow, which drives convective overturning on 105 to 106 year timescales (e.g., McKinnon et al. 2016; Trowbridge et al 2016). Vigorous convection in Sputnik mixes radiolytic products from the surface down into the bulk of the ice, diluting it, and thus maintaining the high albedo of the surface.We propose that the surfaces of Eris and Makemake are similarly refreshed by convection in deep volatile ice deposits, perhaps covering the majority of their surfaces, unlike Pluto's Sputnik, which only covers a small fraction. The local fluxes of energetic radiation dictate production rates for tholin. Assuming steady-state production over the age of the solar system and mixing into the volatile ice, the colors and albedos of the bodies can be used to estimate the thickness of the volatile ice into which the tholin has been diluted through convective mixing. Likewise, for plausible radiogenic internal heat production, lower limits can be set on the thickness of the ice, to support convective mixing. We don't know the rheological properties of mixed N2+CH4 ice, let alone what happens when plausible additional contaminants, such as CO, Ar, C2H2, C2H4, C2H6, etc. are added, but bounding cases for N2-dominated and CH4-dominated ice compositions can be calculated.
  38. Moskovitz, N., Thirouin, A., Mommert, M., et al., (including Skiff, B., Burt, B.), 2017, DPS, 49, 204.04, The Mission Accessible Near-Earth Object Survey (MANOS): Project Status
    The Mission Accessible Near-Earth Object Survey (MANOS) is a physical characterization survey of sub-km, low delta-v, newly discovered near-Earth objects (NEOs). MANOS aims to collect astrometry, lightcurve photometry, and reflectance spectra for a representative sample of these important target of opportunity objects in a rarely observed size range. We employ a diverse set of large aperture (2-8 meter) telescopes and observing modes (queue, remote, classical) to overcome the challenge of observing faint NEOs moving at high non-sidereal rates with short observing windows. We target approximately 10% of newly discovered NEOs every month for follow-up characterization.The first generation MANOS ran from late 2013 to early 2017, using telescopes at Lowell Observatory, NOAO, and the University of Hawaii. This resulted in the collection of data for over 500 targets. These data are continuing to provide new insights into the NEO population as a whole as well as for individual objects of interest. Science highlights include identification of the four fastest rotating minor planets found to date with rotation periods under 20 seconds, constraints on the distribution of NEO morphologies as quantified by de-biased estimates for lightcurve-derived axis ratios, and the compositional distribution of NEOs at sizes under 100 meters.The second generation MANOS will begin in late 2017 and will employ much of the same strategies while continuing to build a comprehensive dataset of NEO physical properties. This will grow the MANOS sample to ~1000 objects and provide the means to better address key questions related to understanding the physical properties of NEOs, their viability as exploration mission targets, and their relationship to Main Belt asteroids and meteorites. This continuation of MANOS will include an increased focus on spectroscopic observations at near-IR wavelengths using a new instrument called NIHTS (the Near-Infrared High-Throughput Spectrograph) at Lowell Observatorys 4.3m Discovery Channel Telescope.We will present key results from the first generation survey and current status and plans for the second generation survey. MANOS is supported by the NASA SSO/NEOO program.
  39. Reddy, V., Kuhn, O., Thirouin, A., et al., 2017, DPS, 49, 204.07, Ground-based Characterization of Earth Quasi Satellite (469219) 2016 HO3
    (469219) 2016 HO3 is a small, <100 meter-size, near-Earth object (NEO) that while orbiting the Sun, also appears to circle around the Earth just beyond the Hill sphere as a Earth quasi-satellite. Only five quasi-satellites have been discovered so far, but 2016 HO3 is the most stable of them. The provenance of this object is unknown. On timescales of many centuries, 2016 HO3 remains within 38-100 lunar distance from us making it a prime target for future robotic and human exploration, provided it can be established it is indeed a natural object. In an effort to constrain its rotation period and surface composition, we observed 2016 HO3 on April 14 and 18 2017 (UTC) with the Large Binocular Telescope (LBT) and the Discovery Channel Telescope (DCT). We derive a rotation period of about 28 minutes based on our lightcurve observations. We obtained low-resolution (R 150 - 500) spectra of 2016 HO3 on 2017 April 14 (UTC) using the pair of MODS spectrographs mounted at the direct Gregorian foci of the LBT, obtaining the entire spectrum from 0.39-0.97 microns simultaneously. The visible wavelength spectrum shows a sharp rise in reflectance between 0.4-0.65 microns with a broad plateau beyond. The scatter near 0.8 microns makes it challenging to confirm the presence of a silicate absorption band at ~1 micron. Color ratios derived from the spectrum all suggest an S taxonomic type. We also derive an updated diameter of 36 meters for 2016 HO3 using an absolute magnitude of 24.3 and S-type albedo of 0.25. The derived rotation period and the spectrum are not uncommon amongst small NEOs, suggesting that 2016 HO3 is a natural object of similar provenance to other small NEOs. NASA Near-Earth Object Observations Program Grant NNX17AJ19G (PI: Reddy) funded parts of this work.
  40. Lewis, B., Stansberry, J., Grundy, W., et al., 2017, DPS, 49, 215.02, 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.
  41. Bosh, A., Zuluaga, C., Levine, S., et al., 2017, DPS, 49, 216.01, Astrometry of the Orcus/Vanth occultation on UT 7 March 2017
    On UT 7 March 2017, Orcus was predicted to occult a star with m=14.3. Observations were made at five observatories: the 0.6-m Astronomical Telescope of the University of Stuttgart (ATUS) at Sierra Remote Observatories (SRO), California; Las Cumbres Observatorys 1-m telescope (ELP) at McDonald Observatory, Fort Davis, Texas; NASAs 3-m InfraRed Telescope Facility (IRTF) on Mauna Kea, Hawaii; the 4.1-m Southern Astrophysical Research telescope (SOAR) on Cerro Pachon, Chile; and the 0.6-m Southeastern Association for Research in Astronomy telescope (SARA-CT) at Cerro Tololo, Chile. While observations at all sites were successful, only twoELP and IRTFobserved solid-body occultation signatures. We will discuss the various predictions for this event and the reasons for the differences among them, including an offset of 130 mas for the star position from the position in the Gaia catalog. The sum of the positive and negative detections place constraints on the geometry of the Orcus/Vanth system, and we present our astrometric results for the geometric solution for this occultation. The implications of the light curve analyses are presented by Sickafoose et al., this conference.
  42. Sickafoose, A., Bosh, A., Levine, S., et al., 2017, DPS, 49, 216.02, A 2017 stellar occultation by Orcus/Vanth
    (90482) Orcus is a large trans-Neptunian object (TNO) of diameter ~900 km, located in the 3:2 orbital resonance with Neptune. This plutino has a satellite, Vanth, approximately 280 km in diameter. Vanth orbits roughly 9000 km from Orcus in a ~9.5-day period. This system is particularly interesting, as Orcus falls between the small, spectrally-bland TNOs and the large TNOs having spectra rich in volatile features, while Vanth might have resulted from either collision or capture.A stellar occultation by Orcus was predicted to occur on 07 March 2017. Observations were made from five sites: the 0.6-m Astronomical Telescope of the University of Stuttgart (ATUS) at Sierra Remote Observatories (SRO), California; Las Cumbres Observatorys 1-m telescope (ELP) at McDonald Observatory, Fort Davis, Texas; NASAs 3-m InfraRed Telescope Facility (IRTF) on Mauna Kea, Hawaii; the 4.1-m Southern Astrophysical Research telescope (SOAR) on Cerro Pachon, Chile; and the 0.6-m Southeastern Association for Research in Astronomy telescope (SARA-CT) at Cerro Tololo, Chile. High-speed, visible-wavelength images were taken at all sites, in addition to simultaneous K-band images at the IRTF. A solid-body occultation was observed at both ELP and the IRTF. Offset midtimes and incompatible light ratios suggest that two different stars were occulted by two different bodies, likely Orcus and Vanth. See Bosh et al. this conference for details of the astrometry for the event. Here, we present results from the observations, including light curves, size and albedo estimates, and upper limits on a possible atmosphere.
  43. Rabinowitz, D., Benecchi, S., Grundy, W., et al., (including Thirouin, A.), 2017, DPS, 49, 216.06, Light Curve observations of the Binary Kuiper Belt Object Manwe-Thorondor
    The binary Kuiper Belt Object (385446) Manwe-Thorondor (aka 2003 QW111) is intriguing for several reasons. Not only are Manwe and Thorondor currently undergoing mutual events, whereby the two ~100-km bodies alternately eclipse and occult each other as seen from Earth [1], but the observed rotational variation implies a rotation for Thorondor that is either synchronous with Manwe ( a period of 11.79 h), or else much longer than 10 days [2]. Here we report new light curve observations using the 8.1-m Gemini South telescope at the time of a predicted mutual event on 2017 July 22-23. Combining these data with our previous observations with the 4.1m SOAR telescope at the time of an earlier mutual event (2016 Aug 25-26), we put precise constraints on the independent rotation states of Manwe and Thorondor.[1] Grundy, W. et al. 2012, Icarus, 220, 74[2] Rabinowitz, D. et al. 2016, AAS DPS meeting #48, astract id.120.10
  44. Singer, K., Knight, K., Stern, S., et al., (including Grundy, W.), 2017, DPS, 49, 221.01, Chaotic Mountain Blocks in Plutos Sputnik Planitia
    One of the first high-resolution Pluto images returned by New Horizons displayed a collection of tall, jagged peaks rising out of the large nitrogen ice sheet informally known as Sputnik Planitia (SP). This mountain range was later revealed to be one of several along the western edge of SP. The mountains are several hundred broken-up blocks of Plutos primarily water ice lithosphere and some retain surface terrains similar to the nearby intact crust surrounding SP. Water ice with some fractures or porosity is likely >5% less dense than solid N2 ice at Plutos temperatures. Thus it is possible the blocks are, or were, floating icebergs or at least partially suspended to the point that some blocks appear to be tilted as if they have faltered (Moore et al., 2016, Science, 351, 1284-1293).We analyze four mountain ranges on the western edge of SP and compare to chaotic terrains on Europa and Mars. The blocks on Pluto have angular planforms but we characterize their size using block surface area converted to an equivalent circular diameter. Topography was used to define block extents. The blocks range in size from 3-30 km in diameter, with a mode of ~8-10 km. Blocks range from 0.2-3.8 km in height, and block height generally increases with block diameter. One or more dark layers can be identified in a few scarp faces, and are at a similar depth to each other and to layers seen in fault and crater walls elsewhere on Pluto. A large N-S trending fault system runs tangential to SP and may be the source of crustal disruption on the western side.On Europa and Mars block sizes vary greatly between different chaos regions, but Conamara Chaos has an average block size of ~5 km in diameter, smaller than that typically seen on Pluto. Also the blocks often transition into fractured terrain still connected to the surround lithosphere at the periphery of the chaos regions. The source regions for the blocks are more obvious on Europa and Mars. Additionally the block heights on Europa and Mars generally do not increase with block size. Thus, the main mechanism of crustal breakup is likely different between these bodies.
  45. Olkin, C., Spencer, J., Grundy, W., et al., 2017, DPS, 49, 221.02, The Color of Pluto from New Horizons
    The New Horizons flyby provided the first high-resolution color maps of Pluto. These maps show the color variegation across the surface from the very red terrain in the equatorial region, to the more neutral colors of the volatile ices in Sputnik Planitia, the blue terrain of east Tombaugh Regio and the yellow hue on Pluto's north pole. There are two distinct color mixing lines in the color-color diagrams derived from images of Pluto. Both mixing lines have an apparent starting point in common: the relatively neutral color volatile-ice covered terrain. One line extends to the dark red terrain exemplified by Cthulu Regio and the other extends to the yellow hue in the northern latitudes. The red color is consistent with a non-ice component on the surface and is consistent with tholins.
  46. Kammer, J., Becker, T., Retherford, K., et al., (including Wasserman, L.), 2017, DPS, 49, 221.03, Probing the Hill Sphere of 2014 MU69 with HST FGS
    During HST GO/DD Program 15003, we observed the July 17, 2017 stellar occultation by the Kuiper Belt object 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 or other debris in the 2014 MU69 system. We used the HST FGS instrument in TRANS F583W mode to collect 40 Hz time resolution photometry of the stellar occultation star for 2 orbits during this observation. We present the results of reduction and calibration of the FGS photometry, accounting for the different photometric sensitivities of the four PMTs of the instrument. From this, we then set limits on rings or other dust opacity within the Hill sphere of 2014 MU69 at distances up to 75,000 km from the main body.
  47. Hanley, J., Grundy, W., Thompson, G., et al., (including Roe, H.), 2017, DPS, 49, 301.02, Methane, Ethane, and Nitrogen Stability on Titan and Other Icy Bodies
    Many outer solar system bodies are likely to have a combination of methane, ethane and nitrogen. In particular the lakes of Titan are known to consist of these species. Understanding the past and current stability of these lakes requires characterizing the interactions of methane and ethane, along with nitrogen, as both liquids and ices. Our cryogenic laboratory setup allows us to explore ices down to 30 K through imaging and transmission and Raman spectroscopy. Our recent work has shown that although methane and ethane have similar freezing points, when mixed they can remain liquid down to 72 K. Concurrently with the freezing point measurements we acquire transmission or Raman spectra of these mixtures to understand how the structural features change with concentration and temperature. Any mixing of these two species together will depress the freezing point of the lake below Titans surface temperature, preventing them from freezing. We will present new results utilizing our recently acquired Raman spectrometer that allow us to explore both the liquid and solid phases of the ternary system of methane, ethane and nitrogen. In particular we will explore the effect of nitrogen on the eutectic of the methane-ethane system. At high pressure we find that the ternary creates two separate liquid phases. Through spectroscopy we determined the bottom layer to be nitrogen rich, and the top layer to be ethane rich. Identifying the eutectic, as well as understanding the liquidus and solidus points of combinations of these species, has implications for not only the lakes on the surface of Titan, but also for the evaporation/condensation/cloud cycle in the atmosphere, as well as the stability of these species on other outer solar system bodies. These results will help interpretation of future observational data, and guide current theoretical models.
  48. Schleicher, D., Eisner, N., Knight, M., et al., (including Thirouin, A.), 2017, DPS, 49, 305.07, CN Jet Morphology and the Very Rapidly Changing Rotation Period of Comet 41P/Tuttle-Giacobini-Kresak
    In the first half of 2017, Comet 41P/Tuttle-Giacobini-Kresak had its best apparition since its first discovery in 1858, remaining within 0.15 AU of Earth for three weeks and within 0.20 AU over a two month interval. These circumstances allowed us to study its coma morphology in search of possible jets, whose appearance and motion as a function of time would yield the rotation period and, with appropriate modeling, the pole orientation of the nucleus and source location(s). Imaging was obtained on a total of 45 nights between February 16 and July 2, using Lowell Observatory's 4.3-m Discovery Channel Telescope, the Hall 1.1-m telescope, and the robotic 0.8-m telescope. All narrowband CN images exhibit either one or two gas jets, and on most nights both jets appear as partial spirals with a clockwise rotation. Only a slow evolution of the jet morphology took place from mid-March to early June, presumably due to viewing geometry changes coupled with seasonal changes. Our coverage in late March was sufficient to rule out aliases of the rotation period, and further revealed a rapidly increasing period from about 24 hr to about 27 hr at the end of the month (Knight et al. 2017, CBET 4377). This rate of increase is roughly consistent with the solution of 19.9 hr found by Farnham et al. (2017, CBET 4375) in early March. Images from April 15 to May 4 yield an accelerating change in periods, passing 48 hr approximately on April 28. This is the fastest rate of change ever measured for a comet nucleus. These and other results, including those from Monte Carlo jet modeling just begun by us, will be presented.These studies were supported by NASA Planetary Astronomy grant NNX14AG81G and the Marcus Cometary Research Fund.
  49. Hsieh, H., Ishiguro, M., Kim, Y., et al., (including Moskovitz, N., Thirouin, A.), 2017, DPS, 49, 305.10, The Reactivations of Main-Belt Comets 238P/READ, 259P/Garradd, and 288P/(300163) 2006 VW139
    We report on the confirmation and monitoring of recurrent activity for main-belt comets (MBCs) 238P/Read and 288P/(300163) 2006 VW139 in 2016 (cf. Agarwal et al. 2016, CBET 4306; Hsieh et al. 2016, CBET 4307), as well as the identification of activity for 288P in Sloan Digital Sky Survey images from November 2000. We will also report on the confirmation of recurrent activity in 2017 (Hsieh et al. 2017, CBET 4388) and the progress of the ongoing monitoring campaign (April 2017 through December 2017) that we are conducting for MBC 259P/Garradd. With these observations, 238P and 288P have now each been observed to be active on three separate orbit passages with intervening periods of inactivity and 259P has been observed to be active on two separate orbit passages, firmly establishing the cometary (i.e., sublimation-driven) nature of their activity. We are currently conducting a multi-facility observing campaign to monitor the photometric and morphological evolution of these objects, using the Canada-France-Hawaii Telescope, the Gemini North and South telescopes (under a Gemini Large and Long Program), the Magellan telescopes, the Discovery Channel Telescope, and the Lulin One-meter Telescope. During their most recent perihelion encounters, 238P was observed to be active as early as 2016 July 8 at a true anomaly of 329 degrees, 288P was observed to be active as early as 2016 June 8 at a true anomaly of 318 degrees, and 259P was observed to be active as early at 2017 April 26 at a true anomaly of 315 degrees. We also report on the results of numerical modeling analyses of the morphological evolution of all three objects aimed at assessing both the properties of their current active episodes and changes in activity strength from one epoch to the next to help constrain the active lifetimes of MBCs, a key parameter for inferring the total number of MBCs in the asteroid belt from survey results. This work was supported by the NASA Solar System Observations program under Grant NNX16AD68G.
  50. Schmidt, C., Leblanc, F., Moore, L., et al., (including Bida, T.), 2017, DPS, 49, 422.01, Detection of Mercury's Potassium Tail
    Ground-based observations of Mercury's exosphere bridge the gap between the MESSENGER and BepiColombo missions and provide a broad counterpart to their in situ measurements. Here we report the first detection of Mercury's potassium tail in both emission lines of the D doublet. The sodium to potassium abundance ratio at 5 planetary radii down-tail is approximately 95, near the mid-point of a wide range of values that have been quoted over the planet's disk. This is several times the Na/K present in atmospheres of the Galilean satellites and more than an order of magnitude above Mercury's usual analogue, the Moon. The observations confirm that Mercury's anomalously high Na/K ratios cannot be explained by differences in neutral loss rates. The width and structure of the Na and K tails is comparable and both exhibit a persistent enhancement in their northern lobe. We interpret this as a signature of Mercury's offset magnetosphere; the exosphere's source rates are locally enhanced at the southern surface, and sloshing from radiation pressure and gravity guides this population into the northern region of the tail.
  51. Buie, M., Porter, S., Terrell, D., et al., (including Wasserman, L.), 2017, DPS, 49, 504.01, Overview of the strategies and results of the 2017 occultation campaigns involving (486958) 2014 MU69
    Three stellar occultation opportunities were identified in 2017 involving the New Horizons extended mission target: (486958) 2014 MU69. The first event was on 2017 June 3 and predicted to be visible from southern South America and southern Africa with a somewhat faint star with g=15.33. The second event was on 2017 June 10 under very difficult observing conditions just 16 from a full moon and the faintest star of the three with g=15.57. The third event was on 2017 July 17 and predicted to be visible from southern Argentina with the brightest star of the three with g=12.60. We pursued each of these events with an observing plan and strategy tuned to the constraints imposed by observing conditions and the anticipated prediction uncertainties. The first and third events were amenable to a ground-based telescope deployment and we fielded 25 telescopes. The second event was possible only with SOFIA (Stratospheric Observatory For Infrared Astronomy). The deployment for the first event involved splitting resources between two continents and a strategy optimized to prevent a null result for a D=40km object. The second event was optimized for the search for dust and rings but had a 75% chance of a solid body event for a D=40 km size. The third event was driven by needing to prevent a null result on a D=10 km size and providing extra conservatism on the ground-track uncertainty while observing from the area of Comodoro Rivadavia, Argentina. All campaigns were successful in recording data essential for the constraint on dust or rings around MU69: June 3, 24 lightcurves; July 10, 1 lightcurve; July 17, 23 lightcurves. Only the last event was able to record solid-body chords from the object with 5 chords detected close to the predicted time and place. We will present an overview of the strategies and basic results of the campaigns. This work would not have been possible without the financial support of the New Horizons mission and NASA, astrometric support of the Gaia mission, and logistical support from Argentina and specifically Comodoro Rivadavia as well as assistance from the US Embassies in Buenos Aires and Cape Town.
  52. Porter, S., Buie, M., Spencer, J., et al., (including Wasserman, L.), 2017, DPS, 49, 504.02, Ultra-High Resolution Orbit Determination of (486958) 2014 MU69: Predicting an Occultation with 1% of an Orbit
    In November 2015, the NASA New Horizons spacecraft burned its thrusters to intercept the cold classical Kuiper Belt Object (486958) 2014 MU69. Then, on July 17, 2017, five small telescopes in Chubut Province, Argentina recorded a solid body occultation of MU69. Both these events required an orbital solution of unprecedented accuracy, as will the January 1, 2019 flyby of MU69 by New Horizons. This was especially difficult because there were no precoveries of MU69 prior to July 2014, it is in an extremely crowded field near the galactic core, and it is faint enough to only be reliably detected by Hubble Space Telescopes Wide Field Camera 3 (WFC3). To accomplish this, we performed an extremely detailed analysis of 237 WFC3 images, down to the subpixel distortion level, in order to produce individual probability distribution functions (PDFs) for the position of MU69 in each WFC3 image. We registered each WFC3 image against a pre-release version of the Gaia DR2 catalog, which produced even smaller residuals than the now-released DR1. We then combined these WFC3+Gaia PDFs with a high-precision few-body numerical integrator and a Monte Carlo Markov Chain (MCMC) sampler to produce a state vector PDF for MU69 at defined epoch. Propagating those state vectors from the epoch produces an instantaneous positional cloud for MU69 at any given time. This positional cloud was then directly translated into a shadow path uncertainty cloud in order to plan the MU69 occultation campaign. We will describe this process of fully propagating errors from WFC3 images to telescope sites on the ground, and also describe refinements for future guiding of New Horizons to its encounter with MU69. We thank NASA, Hubble, Gaia, CONAE, the city of Comodoro Rivadavia, and the government of Argentina for their assistance and support of the MU69 occultation campaign.
  53. Zangari, A., Buie, M., Stern, S., et al., (including Wasserman, L.), 2017, DPS, 49, 504.03, A stellar occultation by (486958) 2014 MU69: results from the 2017 July 17 portable telescope campaign
    On 2017 July 17, (486958) 2014 MU69 passed in front of a star as seen from the area north of Comodoro Rivadavia, in Chubut Province, Argentina. Despite challenging wind conditions, twenty two portable telescopes recorded data of the g'= 12.60 mag star in a 45-minute block centered on the predicted midtime of roughly 03:50 UT. Each telescope was spaced approximately 4 km apart in a picket fence pattern to target an object as small as 10 km. The picket fence spanned roughly 100 km. Five telescopes observed a solid body occultation.Occultation data provide a unique one-dimensional probe of the 2014 MU69 system that is impossible to achieve from direct imaging. These data will allow for fits of the size and shape of 2014 MU69, and from its derived size, the albedo . The occultation data will also aid in navigation of NASAs New Horizons spacecraft toward its January 1, 2019 encounter with 2014 MU69.We will detail the July 17 occultation campaign and present analyses of the light curves from each portable station, including occultation timing and constraints on dust and and other objects in the system derived from the occultation baseline data.This work would not have been possible without the financial support of the New Horizons mission and NASA, astrometric support of the Gaia mission and HST, and logistical support from Argentina, CONAE and specifically Comodoro Rivadavia as well as assistance from the US Embassy in Buenos Aires.
  54. Verbiscer, A., Buie, M., Porter, S., et al., (including Wasserman, L.), 2017, DPS, 49, 504.05, Portable Telescopic Observations of the 3 June 2017 Stellar Occultation by New Horizons Kuiper Extended Mission Target (486958) 2014 MU69
    The New Horizons spacecraft will encounter the cold classical Kuiper Belt Object (486958) 2014 MU69 on 1 January 2019. Because it is extremely faint (V mag ~27), MU69 has only been directly observed by the Hubble Space Telescope since its discovery (by HST) in 2014 (Spencer et al. 2015 EPSC 10, 417S). Current knowledge of the physical properties of MU69 is therefore limited to its red color (F606W-F814W = 0.99 0.18, Benecchi et al. 2017) and a crude estimate on its size (20-40 km) based on association with other cold classical KBO visible albedos (0.04-0.15). Stellar occultations are powerful tools with which to measure the size and shape of objects whose distance and faintness precludes any spatially resolved observations. Here we report the results of a stellar occultation of a g=15.33 magnitude star by MU69 on 3 June 2017. The shadow path crossed both southern Africa and South America. We deployed 12 portable telescopes from Mendoza, Argentina and 13 portable telescopes from Clanwilliam, Western Cape, South Africa. Although 24 of these 25 telescopes successfully observed the occultation star at the predicted event time, no solid body detection appeared in any of the acquired lightcurves. Following the successful detection of MU69 by stellar occultation on 17 July 2017, revised predictions of the location of the shadow path on 3 June now allow the lightcurves obtained on 3 June to place important constraints on the environment surrounding MU69 as well as upper limits on the size of any small satellites in the regions probed. This work would not have been possible without the financial support of NASA, the New Horizons Project, the astrometric support of the Gaia mission, and logistical support from the South African Astronomical Observatory, the US Embassies in Buenos Aires and Pretoria and the US Consulate in Cape Town.
  55. Young, E., Buie, M., Porter, S., et al., (including Wasserman, L.), 2017, DPS, 49, 504.06, Debris search around (486958) 2014 MU69: Results from SOFIA and ground-based occultation campaigns
    The New Horizons spacecraft is scheduled to fly by the cold classical KBO 2014 MU69 on 1-Jan-2019. The spacecraft speed relative to the MU69 will be in excess of 14 km/s. At these encounter velocities, impact with debris could be fatal to the spacecraft. We report on searches for debris in the neighborhood of MU69 conducted from SOFIA and ground-based sites. SOFIA observed the star field around MU69 on 10-Jul-2017 (UT) with their Focal Plane Imager (FPI+), operating at 20 Hz from 7:25 to 8:10 UT, spanning the time of the predicted occultation. Several large fixed telescopes observed the 3-Jun-2017, 10-Jul-2017 and/or the 17-Jul-2017 occultation events, including the 4-meter SOAR telescope, the 8-meter Gemini South telescope, and many 16-inch portable telescopes that were arranged in picket fences in South Africa and Argentina. We report on the light curves from these observing platforms and constraints on the optical depth due to debris or rings within the approximate Hill sphere (about 60,000 km across) of MU69. This work was supported by the New Horizons mission and NASA, with astrometric support from the Gaia mission and logistical support from Argentina and the US embassies in Buenos Aires and CapeTown. At SOAR, data acquisition has been done with a Raptor camera (visitor instrument) funded by the Observatorio Nacional/MCTIC.
  56. Thirouin, A., Sheppard, S., 2017, DPS, 49, 504.11, Contact binaries in the Trans-neptunian Belt
    A contact binary is made up of two objects that are almost touching or in contact with each other. These systems have been found in the Near-Earth Object population, the main belt of asteroids, the Jupiter Trojans, the comet population and even in the Trans-neptunian belt.Several studies suggest that up to 30% of the Trans-Neptunian Objects (TNOs) could be contact binaries (Sheppard & Jewitt 2004, Lacerda 2011). Contact binaries are not resolvable with the Hubble Space Telescope because of the small separation between the system's components (Noll et al. 2008). Only lightcurves with a characteristic V-/U-shape at the minimum/maximum of brightness and a large amplitude can identify these contact binaries. Despite an expected high fraction of contact binaries, 2001 QG298 is the only confirmed contact binary in the Trans-Neptunian belt, and 2003 SQ317 is a candidate to this class of systems (Sheppard & Jewitt 2004, Lacerda et al. 2014).Recently, using the Lowells 4.3m Discovery Channel Telescope and the 6.5m Magellan Telescope, we started a search for contact binaries at the edge of our Solar System. So far, our survey focused on about 40 objects in different dynamical groups of the Trans-Neptunian belt for sparse or complete lightcurves. We report the discovery of 5 new potential contact binaries converting the current estimate of potential/confirmed contact binaries to 7 objects. With one epoch of observations per object, we are not able to model in detail the systems, but we derive estimate for basic information such as shape, size, density of both objects as well as the separation between the systems components. In this work, we will present these new systems, their basic characteristics, and we will discuss the potential main reservoir of contact binaries in the Trans-neptunian belt.
  57. Dahn, C., Harris, H., Subasavage, J., et al., (including Levine, S.), 2017, AJ, 154, 147, CCD Parallaxes for 309 Late-type Dwarfs and Subdwarfs
    New, updated, and/or revised CCD parallaxes determined with the Strand Astrometric Reflector at the Naval Observatory Flagstaff Station are presented. Included are results for 309 late-type dwarf and subdwarf stars observed over the 30+ years that the program operated. For 124 of the stars, parallax determinations from other investigators have already appeared in the literature and we compare the different results. Also included here are new or updated VI photometry on the Johnson-Kron-Cousins system for all but a few of the faintest targets. Together with 2MASS JHK s near-infrared photometry, a sample of absolute magnitude versus color and color versus color diagrams are constructed. Because large proper motion was a prime criterion for targeting the stars, the majority turn out to be either M-type subdwarfs or late M-type dwarfs. The sample also includes 50 dwarf or subdwarf L-type stars, and four T dwarfs. Possible halo subdwarfs are identified in the sample based on tangential velocity, subluminosity, and spectral type. Residuals from the solutions for parallax and proper motion for several stars show evidence of astrometric perturbations.
  58. Egeland, R., Soon, W., Baliunas, S., et al., (including Hall, J.), 2017, IAUS, 328, 329, Evolution of Long Term Variability in Solar Analogs
    Earth is the only planet known to harbor life, therefore we may speculate on how the nature of the Sun-Earth interaction is relevant to life on Earth, and how the behavior of other stars may influence the development of life on their planetary systems. We study the long-term variability of a sample of five solar analog stars using composite chromospheric activity records up to 50 years in length and synoptic visible-band photometry about 20 years long. This sample covers a large range of stellar ages which we use to represent the evolution in activity for solar mass stars. We find that young, fast rotators have an amplitude of variability many times that of the solar cycle, while old, slow rotators have very little variability. We discuss the possible impacts of this variability on young Earth and exoplanet climates.
  59. Llama, J., Shkolnik, E., 2017, IAUS, 328, 356, High Energy Exoplanet Transits
    X-ray and ultraviolet transits of exoplanets allow us to probe the atmospheres of these worlds. High energy transits have been shown to be deeper but also more variable than in the optical. By simulating exoplanet transits using high-energy observations of the Sun, we can test the limits of our ability to accurately measure the properties of these planets in the presence of stellar activity. We use both disk-resolved images of the Solar disk spanning soft X-rays, the ultraviolet, and the optical and also disk-integrated Sun-as-a-star observations of the Ly irradiance to simulate transits over a wide wavelength range. We find that for stars with activity levels similar to the Sun, the planet-to-star radius ratio can be overestimated by up to 50% if the planet occults an active region at high energies. We also compare our simulations to high energy transits of WASP-12b, HD 189733, 55 Cnc b, and GJ 436b.
  60. Fares, R., Bourrier, V., Vidotto, A., et al., (including Llama, J.), 2017, MNRAS, 471, 1246, MOVES - I. The evolving magnetic field of the planet-hosting star HD189733
    HD189733 is an active K dwarf that is, with its transiting hot Jupiter, among the most studied exoplanetary systems. In this first paper of the Multiwavelength Observations of an eVaporating Exoplanet and its Star (MOVES) programme, we present a 2-yr monitoring of the large-scale magnetic field of HD189733. The magnetic maps are reconstructed for five epochs of observations, namely 2013 June-July, 2013 August, 2013 September, 2014 September and 2015 July, using Zeeman-Doppler imaging. We show that the field evolves along the five epochs, with mean values of the total magnetic field of 36, 41, 42, 32 and 37 G, respectively. All epochs show a toroidally dominated field. Using previously published data of Moutou et al. and Fares et al., we are able to study the evolution of the magnetic field over 9 yr, one of the longest monitoring campaigns for a given star. While the field evolved during the observed epochs, no polarity switch of the poles was observed. We calculate the stellar magnetic field value at the position of the planet using the potential field source surface extrapolation technique. We show that the planetary magnetic environment is not homogeneous over the orbit, and that it varies between observing epochs, due to the evolution of the stellar magnetic field. This result underlines the importance of contemporaneous multiwavelength observations to characterize exoplanetary systems. Our reconstructed maps are a crucial input for the interpretation and modelling of our MOVES multiwavelength observations.
  61. Howard, A., Moore, J., White, O., et al., (including Grundy, W.), 2017, Icar, 293, 218, Pluto: Pits and mantles on uplands north and east of Sputnik Planitia
    The highlands region north and east of Sputnik Planitia can be subdivided into seven terrain types based on their physiographic expression. The northern rough uplands are characterized by jagged uplands and broad troughs, and it may contain a deeply-eroded ancient mantle. Dissected terrain has been interpreted to have been eroded by paleo-glaciation. The smooth uplands and pits terrain contains broad, rolling uplands surrounding complexes of pits, some of which contain smooth floors. The uplands are mantled by smooth-surfaced deposits possibly derived from adjacent pits through low-power explosive cryovolcanism or through slow vapor condensation. The eroded smooth uplands appear to have originally been smooth uplands and pits terrain modified by small-scale sublimation pitting. The bright pitted uplands features intricate texturing by reticulate ridges that may have originated by sublimation erosion, volatile condensation, or both. The bladed terrain is characterized by parallel ridges oriented north-south and is discussed in a separate paper. The dark uplands are mantled with reddish deposits that may be atmospherically deposited tholins. Their presence has affected long-term landform evolution. Widespread pit complexes occur on most of the terrain units. Most appear to be associated with tectonic lineations. Some pits are floored by broad expanses of ices, whereas most feature deep, conical depressions. A few pit complexes are enclosed by elevated rims of uncertain origin.
  62. Moore, J., Howard, A., Umurhan, O., et al., (including Grundy, W.), 2017, EPSC, EPSC2017-365, Bladed Terrain on Pluto: Possible Origins and Evolution
    We conclude that Bladed Terrain on Pluto is a deposit of massive CH4, which preferentially precipitates at high elevations, and has since its initial formation, undergone episodes of sublimation erosion that has given this deposit its characteristic texture.
  63. Rivkin, A., Pravec, P., Thomas, C., et al., (including Thirouin, A., Moskovitz, N.), 2017, EPSC, EPSC2017-401, The Remote Observing Working Group for the Asteroid Impact and Deflection Assessment (AIDA)
    The Asteroid Impact and Deflection Assessment (AIDA) is a joint US-European mission concept designed to demonstrate the effectiveness of an kinetic impactor for planetary defense. Ground-based observing is a key component to AIDA and critical for its success. We present the observing campaign we have been conducting of the asteroid Didymos, the AIDA target, and plans for future work.
  64. Oszkiewicz, D., Skiff, B., Warner, B., et al., 2017, EPSC, EPSC2017-743, Asteroid phase-curves from Gaia-calibrated data
    We use asteroid differential photometry gathered in the past decades together with the Gaia stellar catalogue (as photometric standards) to obtain relative magnitudes. The obtained magnitudes are then used to fit the multi-opposition phase curves in several ways depending on data quality.
  65. Alexandersen, M., Benecchi, S., Chen, Y., et al., (including Thirouin, A.), 2017, EPSC, EPSC2017-856, Hyper Suprime-Cam Lightcurve Studies of Trans-Neptunian Objects from the Outer Solar System Origins Survey
    We have obtained one to three nights of light curve observations of 71 TNOs from the Outer Solar System Origin Surbey (OSSOS) using Hyper Suprime-Cam on Subaru Telescope. The large aperture and field of view observed up to 12 objects at once, with r-band magnitudes from 22.5 to 25.1. The light curves have been photometrically calibrated and light curve periods and amplitudes have been estimated. A full analysis of correlations between light curve properties and orbital properties will be presented at EPSC.
  66. Kwiatkowski, T., Oszkiewicz, D., Kryszczynska, A., et al., (including Moskowitz, N., Thirouin, A.), 2017, EPSC, EPSC2017-874, Photometry and model of a Very Small NEA 2015 AZ43
    Studies of the near-Earth Asteroids (NEA) are important because these bodies may collide with the Earth, but may also be a source of raw materials for space industry. We present observations of one such NEA which passed the Earth in Feb 2015. Measurements of its light variations due to the rotation about the spin axis made it possible to derive its shape model, orientation of the spin axis in space and rotation period. Such parameters can help to understand the orbital evolution of these bodies as well as their internal structure.
  67. Massey, P., Neugent, K., Levesque, E., 2017, RSPTA, 375, 20160267, The evolution of massive stars: bridging the gap in the Local Group
    The nearby galaxies of the Local Group can act as our laboratories in helping to bridge the gap between theory and observations. In this review, we will describe the complications of identifying samples of OB stars, yellow and red supergiants, and Wolf-Rayet stars, and what we have so far learned from these studies.

    This article is part of the themed issue 'Bridging the gap: from massive stars to supernovae'.

  68. Henden, A., Levine, S., Welch, D., et al., 2017, EPJWC, 152, 02011, Using APASS and 2GSS for studying variable stars
    The AAVSO Photometric All-Sky Survey (APASS) provides calibrated magnitudes in the range 7 < V < 17 for the entire sky, in the BVugriZsY bandpasses. While primarily designed for 0.02 mag calibration, it provides photometry over a many-year baseline, and also has near daily cadence in the standard field regions on the equator. Likewise, the Second Generation Synoptic Survey (2GSS) is a follow-on to APASS, and will provide daily cadence in two passbands for the entire sky.
  69. Grundy, W., 2017, hst, 15233, Density of transneptunian object 229762 2007 UK126
    Densities provide unique information about bulk composition and interior structure and are key to going beyond the skin-deep view offered by remote-sensing techniques based on photometry, spectroscopy, and polarimetry. They are known for a handful of the relict planetesimals that populate our Solar System's Kuiper belt, revealing intriguing differences between small and large bodies. More and better quality data are needed to address fundamental questions about how planetesimals form from nebular solids, and how distinct materials are distributed through the nebula. Masses from binary orbits are generally quite precise, but a problem afflicting many of the known densities is that they depend on size estimates from thermal emission observations, with large model-dependent uncertainties that dominate the error bars on density estimates. Stellar occultations can provide much more accurate sizes and thus densities, but they depend on fortuitous geometry and thus can only be done for a few particularly valuable binaries. We propose observations of a system where an accurate density can be determined: 229762 2007 UK126. An accurate size is already available from multiple stellar occultation chords. This proposal will determine the mass, and thus the density.
  70. Allen, T., Prato, L., Wright-Garba, N., et al., (including Biddle, L., Skiff, B., Avilez, I., Muzzio, R.), 2017, ApJ, 845, 161, Properties of the Closest Young Binaries. I. DF Taus Unequal Circumstellar Disk Evolution
    We present high-resolution, spatially resolved, near-infrared spectroscopy and imaging of the two components of DF Tau, a young, low-mass, visual binary in the Taurus star-forming region. With these data, we provide a more precise orbital solution for the system, determine component spectral types, radial velocity, veiling and v\sin i values, and construct individual spectral energy distributions. We estimate the masses of both stars to be 0.6 {M} . We find markedly different circumstellar properties for DF Tau A and B: evidence for a disk, such as near-infrared excess and accretion signatures, is clearly present for the primary, while it is absent for the secondary. Additionally, the v\sin i and rotation period measurements show that the secondary is rotating significantly more rapidly than the primary. We interpret these results in the framework of disk-locking and argue that DF Tau A is an example of disk-modulated rotation in a young system. The DF Tau system raises fundamental questions about our assumptions of universal disk formation and evolution.
  71. Boyajian, T., von Braun, K., van Belle, G., et al., 2017, ApJ, 845, 178, Erratum: Stellar Diameters and Temperatures. II. Main-sequence K- and M-stars (2012, ApJ, 757, 112)
    No abstract found.
  72. Santos-Sanz, P., Lellouch, E., Groussin, O., et al., (including Thirouin, A.), 2017, A&A, 604, A95, "TNOs are Cool": A survey of the trans-Neptunian region. XII. Thermal light curves of Haumea, 2003 VS2 and 2003 AZ84 with Herschel/PACS
    Context. Time series observations of the dwarf planet Haumea and the Plutinos 2003 VS2 and 2003 AZ84 with Herschel/PACS are presented in this work. Thermal emission of these trans-Neptunian objects (TNOs) were acquired as part of the "TNOs are Cool" Herschel Space Observatory key programme.
    Aims: We search for the thermal light curves at 100 and 160 m of Haumea and 2003 AZ84, and at 70 and 160 m for 2003 VS2 by means of photometric analysis of the PACS data. The goal of this work is to use these thermal light curves to obtain physical and thermophysical properties of these icy Solar System bodies.
    Methods: When a thermal light curve is detected, it is possible to derive or constrain the object thermal inertia, phase integral and/or surface roughness with thermophysical modeling.
    Results: Haumea's thermal light curve is clearly detected at 100 and 160 m. The effect of the reported dark spot is apparent at 100 m. Different thermophysical models were applied to these light curves, varying the thermophysical properties of the surface within and outside the spot. Although no model gives a perfect fit to the thermal observations, results imply an extremely low thermal inertia (<0.5 J m-2 s-1/2 K-1, hereafter MKS) and a high phase integral (>0.73) for Haumea's surface. We note that the dark spot region appears to be only weakly different from the rest of the object, with modest changes in thermal inertia and/or phase integral. The thermal light curve of 2003 VS2 is not firmly detected at 70 m and at 160 m but a thermal inertia of (2 0.5) MKS can be derived from these data. The thermal light curve of 2003 AZ84 is not firmly detected at 100 m. We apply a thermophysical model to the mean thermal fluxes and to all the Herschel/PACS and Spitzer/MIPS thermal data of 2003 AZ84, obtaining a close to pole-on orientation as the most likely for this TNO.
    Conclusions: For the three TNOs, the thermal inertias derived from light curve analyses or from the thermophysical analysis of the mean thermal fluxes confirm the generally small or very small surface thermal inertias of the TNO population, which is consistent with a statistical mean value mean = 2.5 0.5 MKS.

    Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. PACS: The Photodetector Array Camera and Spectrometer is one of Herschel's instruments.

  73. Thirouin, A., Sheppard, S., Noll, K., 2017, ApJ, 844, 135, 2004 TT357: A Potential Contact Binary in the Trans-Neptunian Belt
    We report photometric observations of the trans-Neptunian object 2004 TT357 obtained in 2015 and 2017 using the 4.3 m Lowells Discovery Channel Telescope. We derive a rotational period of 7.79 0.01 hr and a peak-to-peak lightcurve amplitude of 0.76 0.03 mag. 2004 TT357 displays a large variability that can be explained by a very elongated single object or can be due to a contact/close binary. The most likely scenario is that 2004 TT357 is a contact binary. If it is in hydrostatic equilibrium, we find that the lightcurve can be explained by a system with a mass ratio q min = 0.45 0.05, and a density of min = 2 g cm-3, or less likely a system with q max = 0.8 0.05, and max = 5 g cm-3. Considering a single triaxial ellipsoid in hydrostatic equilibrium, we derive a lower limit to the density of 0.78 g cm-3, and an elongation (a/b) of 2.01 assuming an equatorial view. From Hubble Space Telescope data, we report no resolved companion orbiting 2004 TT357. Despite an expected high fraction of contact binaries in the trans-Neptunian belt, 2001 QG298 is the unique confirmed contact binary in the trans-Neptunian belt, and 2004 TT357 is only the second candidate to this class of systems, with 2003 SQ317.
  74. Simon, M., Guilloteau, S., Di Folco, E., et al., (including Prato, L.), 2017, ApJ, 844, 158, Dynamical Masses of Low-mass Stars in the Taurus and Ophiuchus Star-forming Regions
    We report new dynamical masses for five pre-main sequence (PMS) stars in the L1495 region of the Taurus star-forming region (SFR) and six in the L1688 region of the Ophiuchus SFR. Since these regions have VLBA parallaxes, these are absolute measurements of the stars masses and are independent of their effective temperatures and luminosities. Seven of the stars have masses < 0.6 {M} , thus providing data in a mass range with little data, and of these, six are measured to precision < 5 % . We find eight stars with masses in the range 0.09-1.1 {M} that agree well with the current generation of PMS evolutionary models. The ages of the stars we measured in the Taurus SFR are in the range 1-3 Myr, and < 1 Myr for those in L1688. We also measured the dynamical masses of 14 stars in the ALMA archival data for Akeson & Jensens Cycle 0 project on binaries in the Taurus SFR. We find that the masses of seven of the targets are so large that they cannot be reconciled with reported values of their luminosity and effective temperature. We suggest that these targets are themselves binaries or triples.
  75. Kellogg, K., Prato, L., Torres, G., et al., (including Avilez, I., Wasserman, L., Levine, S., Bosh, A.), 2017, ApJ, 844, 168, The TWA 3 Young Triple System: Orbits, Disks, Evolution
    We have characterized the spectroscopic orbit of the TWA 3A binary and provide preliminary families of probable solutions for the TWA 3A visual orbit, as well as for the wide TWA 3A-B orbit. TWA 3 is a hierarchical triple located at 34 pc in the 10 Myr old TW Hya association. The wide component separation is 1.55 the close pair was first identified as a possible binary almost 20 years ago. We initially identified the 35-day period orbital solution using high-resolution infrared spectroscopy that angularly resolved the A and B components. We then refined the preliminary orbit by combining the infrared data with a reanalysis of our high-resolution optical spectroscopy. The orbital period from the combined spectroscopic solution is 35 days, the eccentricity is 0.63, and the mass ratio is 0.84 although this high mass ratio would suggest that optical spectroscopy alone should be sufficient to identify the orbital solution, the presence of the tertiary B component likely introduced confusion in the blended optical spectra. Using millimeter imaging from the literature, we also estimate the inclinations of the stellar orbital planes with respect to the TWA 3A circumbinary disk inclination and find that all three planes are likely misaligned by at least 30. The TWA 3A spectroscopic binary components have spectral types of M4.0 and M4.5; TWA 3B is an M3. We speculate that the system formed as a triple, is bound, and that its properties were shaped by dynamical interactions between the inclined orbits and disk.
  76. Miles, B., Shkolnik, E., 2017, AJ, 154, 67, HAZMAT. II. Ultraviolet Variability of Low-mass Stars in the GALEX Archive
    The ultraviolet (UV) light from a host star influences a planets atmospheric photochemistry and will affect interpretations of exoplanetary spectra from future missions like the James Webb Space Telescope. These effects will be particularly critical in the study of planetary atmospheres around M dwarfs, including Earth-sized planets in the habitable zone. Given the higher activity levels of M dwarfs compared to Sun-like stars, time-resolved UV data are needed for more accurate input conditions for exoplanet atmospheric modeling. The Galaxy Evolution Explorer (GALEX) provides multi-epoch photometric observations in two UV bands: near-ultraviolet (NUV; 1771-2831 A) and far-ultraviolet (FUV; 1344-1786 A). Within 30 pc of Earth, there are 357 and 303 M dwarfs in the NUV and FUV bands, respectively, with multiple GALEX observations. Simultaneous NUV and FUV detections exist for 145 stars in both GALEX bands. Our analyses of these data show that low-mass stars are typically more variable in the FUV than the NUV. Median variability increases with later spectral types in the NUV with no clear trend in the FUV. We find evidence that flares increase the FUV flux density far more than the NUV flux density, leading to variable FUV to NUV flux density ratios in the GALEX bandpasses.The ratio of FUV to NUV flux is important for interpreting the presence of atmospheric molecules in planetary atmospheres such as oxygen and methane as a high FUV to NUV ratio may cause false-positive biosignature detections. This ratio of flux density in the GALEX bands spans three orders of magnitude in our sample, from 0.008 to 4.6, and is 1 to 2 orders of magnitude higher than for G dwarfs like the Sun. These results characterize the UV behavior for the largest set of low-mass stars to date.
  77. Knight, M., Snodgrass, C., Vincent, J., et al., (including Skiff, B., Schleicher, D.), 2017, MNRAS, 469, S661, Gemini and Lowell observations of 67P/Churyumov-Gerasimenko during the Rosetta mission
    We present observations of comet 67P/Churyumov-Gerasimenko acquired in support of the Rosetta mission. We obtained usable data on 68 nights from 2014 September until 2016 May, with data acquired regularly whenever the comet was observable. We collected an extensive set of near-IR J, H and Ks data throughout the apparition plus visible-light images in g, r, I and z when the comet was fainter. We also obtained broad-band R and narrow-band CN filter observations when the comet was brightest using telescopes at Lowell Observatory. The appearance was dominated by a central condensation and the tail until 2015 June. From 2015 August onwards, there were clear asymmetries in the coma, which enhancements revealed to be due to the presence of up to three features (I.e. jets). The features were similar in all broad-band filters; CN images did not show these features but were instead broadly enhanced in the southeastern hemisphere. Modelling using the parameters from Vincent et al. replicated the dust morphology reasonably well, indicating that the pole orientation and locations of active areas have been relatively unchanged over at least the last three apparitions. The dust production, as measured by A(0)f peaked 30 d after perihelion and was consistent with predictions from previous apparitions. A(0)f as a function of heliocentric distance was well fitted by a power law with slope -4.2 from 35 to 120 d post-perihelion. We detected photometric evidence of apparent outbursts on 2015 August 22 and 2015 September 19, although neither was discernible morphologically in this data set.
  78. Gregg, M., West, M., 2017, gcf, 4, Virgo Intergalactic Globulars from the Sloan Survey
    We have identified a new sample of Virgo intergalactic globular clusters (IGCs) and ultra compact dwarfs (UCDs) which have been serendipitously observed to date in Sloan Survey spectroscopy. There are 23 new objects with secure redshifts, all relatively red point sources with reliable velocities placing them at Virgo distances. They are spread widely across Virgo, significantly extending the spatial distribution of Virgo IGCs and UCDs to regions outside the well-studied M87 core region. The new sample are generally fainter, bluer, and probably more metal poor on average than the more centrally located, previously known objects. This systematic change carries information about the formation and continued evolution by accretion of the Virgo cluster, indicating a transition to less massive and less luminous objects being tidally disrupted in the outskirts now and in the recent past, compared to conditions in the inner cluster at early epochs.
  79. West, M., 2017, gcf, 10, Ten Billion Years of Brightest Cluster Galaxy Alignments
    Astronomers long assumed that galaxies are randomly oriented in space. However, it's now clear that some have preferred orientations with respect to their surroundings. Chief among these are the giant ellipticals found at the centers of rich galaxy clusters, whose major axes are often aligned with those of their host clusters - a remarkable coherence of structures over millions of light years. A better understanding of these alignments can yield new insights into the processes that have shaped galaxies over the history of the universe. Using Hubble Space Telescope observations of high-redshift galaxy clusters, we show for the first time that such alignments are seen at epochs when the universe was only one-third its current age. These results suggest that the brightest galaxies in clusters are the product of a special formation history, one influenced by development of the cosmic web over billions of years.
  80. Gregg, M., West, M., 2017, gcf, 13, Observing RAM Pressure Stripping and Morphological Transformation in the Coma Cluster
    The two largest spirals in the Coma cluster, NGC4911 and NGC4921, are being vigorously ram-pressure stripped by the hot intracluster medium. Our HST ACS and WFC3 images have revealed galactic scale shock fronts, giant "Pillars of Creation", rivulets of dust, and spatially coherent star formation in these grand design spirals. We have now obtained HST WFC3 imaging of five additional large Coma spirals to search for and investigate the effects of ram pressure stripping across the wider cluster environment. The results are equally spectacular as the first two examples. The geometry of the interactions in some cases allows an estimation of the various time scales involved, including gas flows out of the disk leading to creation of the ICM, and the attendant triggered star formation in the galaxy disks. The global star formation patterns yield insights into the spatial and temporal ISM-ICM interactions driving cluster galaxy evolution and ultimately transforming morphologies from spiral to S0. These processes were much more common in the early Universe when the intergalactic and intracluster components were initially created from stripping and destruction of member galaxies.
  81. Zellem, R., Swain, M., Roudier, G., et al., (including Llama, J.), 2017, ApJ, 844, 27, Forecasting the Impact of Stellar Activity on Transiting Exoplanet Spectra
    Exoplanet host star activity, in the form of unocculted starspots or faculae, alters the observed transmission and emission spectra of the exoplanet. This effect can be exacerbated when combining data from different epochs if the stellar photosphere varies between observations due to activity. Here, we present a method to characterize and correct for relative changes due to stellar activity by exploiting multi-epoch (slant 2 visits/transits) observations to place them in a consistent reference frame. Using measurements from portions of the planets orbit where negligible planet transmission or emission can be assumed, we determine changes to the stellar spectral amplitude. With the analytical methods described here, we predict the impact of stellar variability on transit observations. Supplementing these forecasts with Kepler-measured stellar variabilities for F-, G-, K-, and M-dwarfs, and predicted transit precisions by the James Webb Space Telescopes (JWST) NIRISS, NIRCam, and MIRI, we conclude that stellar activity does not impact infrared transiting exoplanet observations of most presently known or predicted TESS targets by current or near-future platforms, such as JWST, as activity-induced spectral changes are below the measurement precision.
  82. Zavala, R., Hummel, C., Boboltz, D., et al., (including Shaffer, D.), 2017, ApJL, 843, L18, Erratum: The Algol Triple System Spatially Resolved at Optical Wavelengths (2010, ApJL, 715, L44)
    No abstract found.
  83. West, M., de Propris, R., Bremer, M., et al., 2017, NatAs, 1, 0157, Ten billion years of brightest cluster galaxy alignments
    A galaxy's orientation is one of its most basic observable properties. Astronomers once assumed that galaxies are randomly oriented in space; however, it is now clear that some have preferred orientations with respect to their surroundings. Chief among these are giant elliptical galaxies found in the centres of rich galaxy clusters. Numerous studies have shown that the major axes of these galaxies often share the same orientation as the surrounding matter distribution on larger scales1,2,3,4,5,6. Using Hubble Space Telescope observations of 65 distant galaxy clusters, we show that similar alignments are seen at earlier epochs when the Universe was only one-third of its current age. These results suggest that the brightest galaxies in clusters are the product of a special formation history, one influenced by development of the cosmic web over billions of years.
  84. Dias-Oliveira, A., Sicardy, B., Ortiz, J., et al., (including Thirouin, A.), 2017, AJ, 154, 22, Study of the Plutino Object (208996) 2003 AZ84 from Stellar Occultations: Size, Shape, and Topographic Features
    We present results derived from four stellar occultations by the plutino object (208996) 2003 AZ84, detected on 2011 January 8 (single-chord event), 2012 February 3 (multi-chord), 2013 December 2 (single-chord), and 2014 November 15 (multi-chord). Our observations rule out an oblate spheroid solution for 2003 AZ84's shape. Instead, assuming hydrostatic equilibrium, we find that a Jacobi triaxial solution with semiaxes (470+/- 20) (383+/- 10) (245+/- 8) km can better account for all our occultation observations. Combining these dimensions with the rotation period of the body (6.75 hr) and the amplitude of its rotation light curve, we derive a density =0.87+/- 0.01 g cm-3, a geometric albedo {p}V=0.097+/- 0.009. A grazing chord observed during the 2014 occultation reveals a topographic feature along 2003 AZ84's limb, which can be interpreted as an abrupt chasm of width 23 km and depth > 8 km, or a smooth depression of width 80 km and depth 13 km (or an intermediate feature between those two extremes).
  85. Bida, T., Killen, R., 2017, Icar, 289, 227, Observations of the minor species Al and Fe in Mercury's exosphere
    We report here on the first observational evidence of Al and Fe in the exosphere of Mercury, based on measurements of resolved emission lines of these metals with Keck-1/HIRES. Al emission was observed on two separate runs, in 2008 and 2013, with tangent column densities of 3.1 1.0 and 4.0 1.5 107 Al atoms cm-2 at altitudes of 1185 and 1870 km (1.5 and 1.75 RM). The Al radiative intensity was seen to increase where the slit crossed the planetary penumbral shadow, and then decrease monotonically with altitude. Fe emission has been observed once, in 2009, indicating an extended source. We also present observed 3- Ca+ upper limits near Mercury's equatorial anti-solar limb, from which an abundance limit of 4.0 106 cm-2 at 1650 km altitude is derived for the Ca ion.

    A simple model for zenith column abundances of the neutral species yields 1.9-5.2 107 Al cm-2, and 8.2 108 Fe cm-2. The observations appear to be consistent with production of these species by impact vaporization, with a large fraction of the Al ejecta in molecular form, and that for Fe in mixed atomic and molecular forms. The scale height of the Al gas is consistent with a kinetic temperature of 6100-8000 K. The apparent high temperature and low density of the Al gas would suggest that it may be produced by dissociation of molecules.

  86. Adamo, A., Ryon, J., Messa, M., et al., (including Hunter, D.), 2017, ApJ, 841, 131, Legacy ExtraGalactic UV Survey with The Hubble Space Telescope: Stellar Cluster Catalogs and First Insights Into Cluster Formation and Evolution in NGC 628
    We report the large effort that is producing comprehensive high-level young star cluster (YSC) catalogs for a significant fraction of galaxies observed with the Legacy ExtraGalactic UV Survey (LEGUS) Hubble treasury program. We present the methodology developed to extract cluster positions, verify their genuine nature, produce multiband photometry (from NUV to NIR), and derive their physical properties via spectral energy distribution fitting analyses. We use the nearby spiral galaxy NGC 628 as a test case for demonstrating the impact that LEGUS will have on our understanding of the formation and evolution of YSCs and compact stellar associations within their host galaxy. Our analysis of the cluster luminosity function from the UV to the NIR finds a steepening at the bright end and at all wavelengths suggesting a dearth of luminous clusters. The cluster mass function of NGC 628 is consistent with a power-law distribution of slopes -2 and a truncation of a few times 105 {M} . After their formation, YSCs and compact associations follow different evolutionary paths. YSCs survive for a longer time frame, confirming their being potentially bound systems. Associations disappear on timescales comparable to hierarchically organized star-forming regions, suggesting that they are expanding systems. We find mass-independent cluster disruption in the inner region of NGC 628, while in the outer part of the galaxy there is little or no disruption. We observe faster disruption rates for low mass (104 {M} ) clusters, suggesting that a mass-dependent component is necessary to fully describe the YSC disruption process in NGC 628.

    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, Inc., under NASA contract NAS 5-26555.

  87. Benedict, G., Franz, O., Wasserman, L., 2017, AAS, 230, 217.01, The Multiple-component Binary Hyad, vA 351 - a Progress Report
    We extend results first announced by Franz et al. (1998) in the abstract, http://adsabs.harvard.edu/abs/1998AAS...19310207F ,that identified vA 351 = H346 in the Hyades as a multiple star system containing a white dwarf. With HST/FGS fringe tracking and scanning, spanning four years, we establish a parallax, relative orbit, and mass fraction for the A-B components, with a period, P~5.47y. With ground-based radial velocities from the McDonald Observatory Struve 2.1m telescope and Sandiford Spectrograph, spanning 14 years, we find that component B consists of BC, two M dwarf stars orbiting with a very short period (P(BC)~0.75 days), having a mass ratio C/B~0.94. We confirm that the total mass of the system can only be reconciled with the distance and component photometry by including a fainter, higher mass component, proposed to be a ~0.8Msun white dwarf. Thus, the quadruple system consists of three M dwarfs (A,B,C) and one white dwarf (D). The M dwarf masses and absolute magnitudes are consistent with the Benedict et al. (2016, http://adsabs.harvard.edu/abs/2016AJ....152..141B) lower Main Sequence Mass-Luminosity Relation. The radial velocity signal has so far yielded a signature only for the short-period BC orbital motion. Velocities from H- and He I emission lines confirm the BC period from absorption lines, with similar (He I) and higher (H-) velocity amplitudes.
  88. McKinnon, W., Stern, S., Weaver, H., et al., (including Grundy, W.), 2017, Icar, 287, 2, Origin of the Pluto-Charon system: Constraints from the New Horizons flyby
    New Horizon's accurate determination of the sizes and densities of Pluto and Charon now permit precise internal models of both bodies to be constructed. Assuming differentiated rock-ice structures, we find that Pluto is close to 2/3 solar-composition anhydrous rock by mass and Charon 3/5 solar-composition anhydrous rock by mass. Pluto and Charon are closer to each other in density than to other large (1000-km diameter) Kuiper belt bodies. Despite this, we show that neither the possible presence of an ocean under Pluto's water ice shell (and no ocean within Charon), nor enhanced porosity at depth in Charon's icy crust compared with that of Pluto, are sufficient to make Pluto and Charon's rock mass fractions match. All four small satellites (Styx, Nix, Kerberos, Hydra) appear much icier in comparison with either Pluto or Charon. In terms of a giant impact origin, both these inferences are most consistent with the relatively slow collision of partly differentiated precursor bodies (Canup, Astrophys. J. 141, 35, 2011). This is in turn consistent with dynamical conditions in the ancestral Kuiper belt, but implies that the impact precursors themselves accreted relatively late and slowly (to limit 26Al and accretional heating). The iciness of the small satellites is not consistent with direct formation of the Pluto-Charon system from a streaming instability in the solar nebula followed by prompt collapse of gravitationally bound ;pebble piles,; a proposed formation mechanism for Kuiper belt binaries (Nesvorny et al., Astron. J. 140, 785-793, 2010). Growth of Pluto-scale bodies by accretion of pebbles in the ancestral Kuiper belt is not ruled out, however, and may be needed to prevent the precursor bodies from fully differentiating, due to buried accretional heat, prior to the Charon-forming impact.
  89. Binzel, R., Earle, A., Buie, M., et al., (including Grundy, W.), 2017, Icar, 287, 30, Climate zones on Pluto and Charon
    We give an explanatory description of the unusual ;climate zones; on Pluto that arise from its high obliquity (mean 115) and high amplitude (12) of obliquity oscillation over a 2.8 million year period. The zones we describe have astronomically defined boundaries and do not incorporate atmospheric circulation. For such a high mean obliquity, the lines of tropics (greatest latitudes where the Sun can be overhead) cycle closer to each pole than does each arctic circle, which in turn cycle nearly to the equator. As a consequence in an astronomical context, Pluto is more predominantly ;tropical; than ;arctic.; Up to 97% of Pluto's surface area can experience overhead Sun when the obliquity cycle is at its minimum of 103. At this same obliquity phase (most recently occurring 0.8 Myr ago), 78% of Pluto's surface experienced prolonged intervals without sunlight or ;arctic winter; (and corresponding ;arctic summer;). The intersection of these climate zones implies that a very broad range of Pluto's latitudes (spanning 13-77 in each hemisphere; 75% of the total surface area) are both tropical and arctic. While some possible correlations to these climate zones are suggested by comparison with published maps of Pluto and Charon yielded by the New Horizons mission, in this work we present a non-physical descriptive analysis only. For example, the planet-wide dark equatorial band presented by Stern et al. (2015; Science, 350, 292-299) corresponds to Pluto's permanent ;diurnal zone.; In this zone spanning latitudes within 13 of the equator, day-night cycles occur each Pluto rotation (6.4 days) such that neither ;arctic winter; nor ;arctic summer; has been experienced in this zone for at least 20 million years. The stability of this and other climate zones may extend over several Gyr. Temperature modeling shows that the continuity of diurnal cycles in this region may be the key factor enabling a long-term stability for the high albedo contrast between Tombaugh Regio adjacent to the dark Cthulhu Regio (Earle et al. (2017) Icarus, special issue, submitted). (All names are informal.) Charon's synchronous alignment with Pluto dictates that both bodies in the binary pair have the same climate zone structure, but any effects on Charon's morphology may be limited if volatile transport there is minimal or absent. Cold-trapped methane-rich volatiles on top of its water ice surface may be responsible for forming Charon's dark red north polar cap (Grundy et al., 2016b), and we note the most concentrated area of this feature resides almost entirely within the permanent ;polar zone; (above 77 latitude) where the Sun never reaches the overhead point and arctic seasons have been most consistently experienced over at least tens of millions of years. Pluto is not alone among bodies in the Kuiper belt (and uranian satellites) in having high obliquities, overlapping tropical and arctic zones, and latitude bands that remain in a continuous diurnal cycle over long terms.
  90. Earle, A., Binzel, R., Young, L., et al., (including Grundy, W.), 2017, Icar, 287, 37, Long-term surface temperature modeling of Pluto
    NASA's New Horizons' reconnaissance of the Pluto system has revealed at high resolution the striking albedo contrasts from polar to equatorial latitudes on Pluto, as well as the sharpness of boundaries for longitudinal variations. These contrasts suggest that Pluto must undergo dynamic evolution that drives the redistribution of volatiles. Using the New Horizons results as a template, we explore the surface temperature variations driven seasonally on Pluto considering multiple timescales. These timescales include the current orbit (248 years) as well as the timescales for obliquity precession (peak-to-peak amplitude of 23 over 3 million years) and regression of the orbital longitude of perihelion (3.7 million years). These orbital variations create epochs of ;Extreme Seasons; where one pole receives a short, relatively warm summer and long winter, while the other receives a much longer, but less intense summer and short winter. We use thermal modeling to build upon the long-term insolation history model described by Earle and Binzel (2015) and investigate how these seasons couple with Pluto's albedo contrasts to create temperature effects. From this study we find that a bright region at the equator, once established, can become a site for net deposition. We see the region informally known as Sputnik Planitia as an example of this, and find it will be able to perpetuate itself as an ;always available; cold trap, thus having the potential to survive on million year or substantially longer timescales. Meanwhile darker, low-albedo, regions near the equator will remain relative warm and generally not attract volatile deposition. We argue that the equatorial region is a ;preservation zone; for whatever albedo is seeded there. This offers insight as to why the equatorial band of Pluto displays the planet's greatest albedo contrasts.
  91. Howett, C., Parker, A., Olkin, C., et al., (including Grundy, W.), 2017, Icar, 287, 140, Inflight radiometric calibration of New Horizons' Multispectral Visible Imaging Camera (MVIC)
    We discuss two semi-independent calibration techniques used to determine the inflight radiometric calibration for the New Horizons' Multi-spectral Visible Imaging Camera (MVIC). The first calibration technique compares the measured number of counts (DN) observed from a number of well calibrated stars to those predicted using the component-level calibration. The ratio of these values provides a multiplicative factor that allows a conversation between the preflight calibration to the more accurate inflight one, for each detector. The second calibration technique is a channel-wise relative radiometric calibration for MVIC's blue, near-infrared and methane color channels using Hubble and New Horizons observations of Charon and scaling from the red channel stellar calibration. Both calibration techniques produce very similar results (better than 7% agreement), providing strong validation for the techniques used. Since the stellar calibration described here can be performed without a color target in the field of view and covers all of MVIC's detectors, this calibration was used to provide the radiometric keyword values delivered by the New Horizons project to the Planetary Data System (PDS). These keyword values allow each observation to be converted from counts to physical units; a description of how these keyword values were generated is included. Finally, mitigation techniques adopted for the gain drift observed in the near-infrared detector and one of the panchromatic framing cameras are also discussed.
  92. Howett, C., Ennico, K., Olkin, C., et al., (including Grundy, W.), 2017, Icar, 287, 152, Charon's light curves, as observed by New Horizons' Ralph color camera (MVIC) on approach to the Pluto system
    Light curves produced from color observations taken during New Horizons' approach to the Pluto-system by its Multi-spectral Visible Imaging Camera (MVIC, part of the Ralph instrument) are analyzed. Fifty seven observations were analyzed, they were obtained between 9th April and 3rd July 2015, at a phase angle of 14.5 to 15.1, sub-observer latitude of 51.2 N to 51.5 N, and a sub-solar latitude of 41.2N. MVIC has four color channels; all are discussed for completeness but only two were found to produce reliable light curves: Blue (400-550 nm) and Red (540-700 nm). The other two channels, Near Infrared (780-975 nm) and Methane-Band (860-910 nm), were found to be potentially erroneous and too noisy respectively. The Blue and Red light curves show that Charon's surface is neutral in color, but slightly brighter on its Pluto-facing hemisphere. This is consistent with previous studies made with the Johnson B and V bands, which are at shorter wavelengths than that of the MVIC Blue and Red channel respectively.
  93. Robbins, S., Singer, K., Bray, V., et al., (including Grundy, W.), 2017, Icar, 287, 187, Craters of the Pluto-Charon system
    NASA's New Horizons flyby mission of the Pluto-Charon binary system and its four moons provided humanity with its first spacecraft-based look at a large Kuiper Belt Object beyond Triton. Excluding this system, multiple Kuiper Belt Objects (KBOs) have been observed for only 20 years from Earth, and the KBO size distribution is unconstrained except among the largest objects. Because small KBOs will remain beyond the capabilities of ground-based observatories for the foreseeable future, one of the best ways to constrain the small KBO population is to examine the craters they have made on the Pluto-Charon system. The first step to understanding the crater population is to map it. In this work, we describe the steps undertaken to produce a robust crater database of impact features on Pluto, Charon, and their two largest moons, Nix and Hydra. These include an examination of different types of images and image processing, and we present an analysis of variability among the crater mapping team, where crater diameters were found to average 10% uncertainty across all sizes measured (0.5-300 km). We also present a few basic analyses of the crater databases, finding that Pluto's craters' differential size-frequency distribution across the encounter hemisphere has a power-law slope of approximately -3.1 0.1 over diameters D 15-200 km, and Charon's has a slope of -3.0 0.2 over diameters D 10-120 km; it is significantly shallower on both bodies at smaller diameters. We also better quantify evidence of resurfacing evidenced by Pluto's craters in contrast with Charon's. With this work, we are also releasing our database of potential and probable impact craters: 5287 on Pluto, 2287 on Charon, 35 on Nix, and 6 on Hydra.
  94. Buratti, B., Hofgartner, J., Hicks, M., et al., (including Grundy, W.), 2017, Icar, 287, 207, Global albedos of Pluto and Charon from LORRI New Horizons observations
    The exploration of the Pluto-Charon system by the New Horizons spacecraft represents the first opportunity to understand the distribution of albedo and other photometric properties of the surfaces of objects in the Solar System's ;Third Zone; of distant ice-rich bodies. Images of the entire illuminated surface of Pluto and Charon obtained by the Long Range Reconnaissance Imager (LORRI) camera provide a global map of Pluto that reveals surface albedo variegations larger than any other Solar System world except for Saturn's moon Iapetus. Normal reflectances on Pluto range from 0.08-1.0, and the low-albedo areas of Pluto are darker than any region of Charon. Charon exhibits a much blander surface with normal reflectances ranging from 0.20-0.73. Pluto's albedo features are well-correlated with geologic features, although some exogenous low-albedo dust may be responsible for features seen to the west of the area informally named Tombaugh Regio. The albedo patterns of both Pluto and Charon are latitudinally organized, with the exception of Tombaugh Regio, with darker regions concentrated at the Pluto's equator and Charon's northern pole. The phase curve of Pluto is similar to that of Triton, the large moon of Neptune believed to be a captured Kuiper Belt Object (KBO), while Charon's is similar to that of the Moon. Preliminary Bond albedos are 0.25 0.03 for Charon and 0.72 0.07 for Pluto. Maps of an approximation to the Bond albedo for both Pluto and Charon are presented for the first time. Our work shows a connection between very high albedo (near unity) and planetary activity, a result that suggests the KBO Eris may be currently active.
  95. Protopapa, S., Grundy, W., Reuter, D., et al., 2017, Icar, 287, 218, Pluto's global surface composition through pixel-by-pixel Hapke modeling of New Horizons Ralph/LEISA data
    On July 14th 2015, NASA's New Horizons mission gave us an unprecedented detailed view of the Pluto system. The complex compositional diversity of Pluto's encounter hemisphere was revealed by the Ralph/LEISA infrared spectrometer on board of New Horizons. We present compositional maps of Pluto defining the spatial distribution of the abundance and textural properties of the volatiles methane and nitrogen ices and non-volatiles water ice and tholin. These results are obtained by applying a pixel-by-pixel Hapke radiative transfer model to the LEISA scans. Our analysis focuses mainly on the large scale latitudinal variations of methane and nitrogen ices and aims at setting observational constraints to volatile transport models. Specifically, we find three latitudinal bands: the first, enriched in methane, extends from the pole to 55N, the second dominated by nitrogen, continues south to 35N, and the third, composed again mainly of methane, reaches 20N. We demonstrate that the distribution of volatiles across these surface units can be explained by differences in insolation over the past few decades. The latitudinal pattern is broken by Sputnik Planitia, a large reservoir of volatiles, with nitrogen playing the most important role. The physical properties of methane and nitrogen in this region are suggestive of the presence of a cold trap or possible volatile stratification. Furthermore our modeling results point to a possible sublimation transport of nitrogen from the northwest edge of Sputnik Planitia toward the south.
  96. Schmitt, B., Philippe, S., Grundy, W., et al., 2017, Icar, 287, 229, Physical state and distribution of materials at the surface of Pluto from New Horizons LEISA imaging spectrometer
    From Earth based observations Pluto is known to be the host of N2, CH4 and CO ices and also a dark red material. Very limited spatial distribution information is available from rotational visible and near-infrared spectral curves obtained from hemispheric measurements. In July 2015 the New Horizons spacecraft reached Pluto and its satellite system and recorded a large set of data. The LEISA spectro-imager of the RALPH instruments are dedicated to the study of the composition and physical state of the materials composing the surface. In this paper we report a study of the distribution and physical state of the ices and non-ice materials on Pluto's illuminated surface and their mode and degree of mixing. Principal Component analysis as well as various specific spectral indicators and correlation plots are used on the first set of 2 high resolution spectro-images from the LEISA instrument covering the whole illuminated face of Pluto at the time of the New Horizons encounter. Qualitative distribution maps have been obtained for the 4 main condensed molecules, N2, CH4, CO, H2O as well as for the visible-dark red material. Based on specific spectral indicators, using either the strength or the position of absorption bands, these 4 molecules are found to indicate the presence of 3 different types of ices: N2-rich:CH4:CO ices, CH4-rich(:CO:N2?) ices and H2O ice. The mixing lines between these ices and with the dark red material are studied using scatter plots between the various spectral indicators. CH4 is mixed at the molecular level with N2, most probably also with CO, thus forming a ternary molecular mixture that follows its phase diagram with low solubility limits. The occurrence of a N2-rich - CH4-rich ices mixing line associated with a progressive decrease of the CO/CH4 ratio tells us that a fractionation sublimation sequence transforms one type of ice to the other forming either a N2-rich - CH4-rich binary mixture at the surface or an upper CH4-rich ice crust that may hide the N2-rich ice below. The strong CH4-rich - H2O mixing line witnesses the subsequent sublimation of the CH4-rich ice lag left behind by the N2:CO sublimation (N spring-summer), or a direct condensation of CH4 ice on the cold H2O ice (S autumn). The weak mixing line between CH4-containing ices and the dark red material and the very sharp spatial transitions between these ices and this non-volatile material are probably due to thermal incompatibility. Finally the occurrence of a H2O ice - red material mixing line advocates for a spatial mixing of the red material covering H2O ice, with possibly a small amount intimately mixed in water ice. From this analysis of the different materials distribution and their relative mixing lines, H2O ice appears to be the substratum on which other ices condense or non-volatile organic material is deposited from the atmosphere. N2-rich ices seem to evolve to CH4-dominated ices, possibly still containing traces of CO and N2, as N2 and CO sublimate away. The spatial distribution of these materials is very complex.

    The high spatial definition of all these composition maps, as well as those at even higher resolution that will be soon available, will allow us to compare them with Pluto's geologic features observed by LORRI panchromatic and MVIC multispectral imagers to better understand the geophysical processes in action at the surface of this astonishingly active frozen world.

  97. White, O., Moore, J., McKinnon, W., et al., (including Grundy, W.), 2017, Icar, 287, 261, Geological mapping of Sputnik Planitia on Pluto
    The geology and stratigraphy of the feature on Pluto informally named Sputnik Planitia is documented through geologic mapping at 1:2,000,000 scale. All units that have been mapped are presently being affected to some degree by the action of flowing N2 ice. The N2 ice plains of Sputnik Planitia display no impact craters, and are undergoing constant resurfacing via convection, glacial flow and sublimation. Condensation of atmospheric N2 onto the surface to form a bright mantle has occurred across broad swathes of Sputnik Planitia, and appears to be partly controlled by Pluto's obliquity cycles. The action of N2 ice has been instrumental in affecting uplands terrain surrounding Sputnik Planitia, and has played a key role in the disruption of Sputnik Planitia's western margin to form chains of blocky mountain ranges, as well in the extensive erosion by glacial flow of the uplands to the east of Sputnik Planitia.
  98. Moore, J., Howard, A., Umurhan, O., et al., (including Grundy, W.), 2017, Icar, 287, 320, Sublimation as a landform-shaping process on Pluto
    Fields of pits, both large and small, in Tombaugh Regio (Sputnik Planitia, and the Pitted Uplands to the east), and along the scarp of Piri Rupes, are examples of landscapes on Pluto where we conclude that sublimation drives their formation and evolution. Our heuristic modeling closely mimics the form, spacing, and arrangement of a variety of Tombaugh Regio's pits. Pluto's sublimation modified landforms appear to require a significant role for (diffusive) mass wasting as suggested by our modeling. In our models, the temporal evolution of pitted surfaces is such that initially lots of time passes with little happening, then eventually, very rapid development of relief and rapid sublimation. Small pits on Sputnik Planitia are consistent with their formation in N2-dominated materials. As N2-ice readily flows, some other ``stiffer'' volatile ice may play a role in supporting the relief of sublimation degraded landforms that exhibit several hundred meters of relief. A strong candidate is CH4, which is spectroscopically observed to be associated with these features, but the current state of rheological knowledge for CH4 ice at Pluto conditions is insufficient for a firm assessment.
  99. Snodgrass, C., A'Hearn, M., Aceituno, F., et al., (including Schleicher, D.), 2017, RSPTA, 375, 20160249, The 67P/Churyumov-Gerasimenko observation campaign in support of the Rosetta mission
    We present a summary of the campaign of remote observations that supported the European Space Agency's Rosetta mission. Telescopes across the globe (and in space) followed comet 67P/Churyumov-Gerasimenko from before Rosetta's arrival until nearly the end of the mission in September 2016. These provided essential data for mission planning, large-scale context information for the coma and tails beyond the spacecraft and a way to directly compare 67P with other comets. The observations revealed 67P to be a relatively `well-behaved' comet, typical of Jupiter family comets and with activity patterns that repeat from orbit to orbit. Comparison between this large collection of telescopic observations and the in situ results from Rosetta will allow us to better understand comet coma chemistry and structure. This work is just beginning as the mission ends-in this paper, we present a summary of the ground-based observations and early results, and point to many questions that will be addressed in future studies.

    This article is part of the themed issue 'Cometary science after Rosetta'.

  100. Neugent, K., Massey, P., Hillier, D., et al., 2017, ApJ, 841, 20, The Evolution and Physical Parameters of WN3/O3s: A New Type of Wolf-Rayet Star
    As part of a search for Wolf-Rayet (WR) stars in the Magellanic Clouds, we have discovered a new type of WR star in the Large Magellanic Cloud (LMC). These stars have both strong emission lines, as well as He II and Balmer absorption lines and spectroscopically resemble a WN3 and O3V binary pair. However, they are visually too faint to be WN3+O3V binary systems. We have found nine of these WN3/O3s, making up 6% of the population of LMC WRs. Using cmfgen, we have successfully modeled their spectra as single stars and have compared the physical parameters with those of more typical LMC WNs. Their temperatures are around 100,000 K, a bit hotter than the majority of WN stars (by around 10,000 K), though a few hotter WNs are known. The abundances are what you would expect for CNO equilibrium. However, most anomalous are their mass-loss rates, which are more like that of an O-type star than a WN star. While their evolutionary status is uncertain, their low mass-loss rates and wind velocities suggest that they are not products of homogeneous evolution. It is possible instead that these stars represent an intermediate stage between O stars and WNs. Since WN3/O3 stars are unknown in the Milky Way, we suspect that their formation depends upon metallicity, and we are investigating this further by a deep survey in M33, which possesses a metallicity gradient.

    This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. It is additionally based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations were associated with program GO-13780.

  101. Daemgen, S., Todorov, K., Silva, J., et al., (including Garcia, E.), 2017, A&A, 601, A65, Mid-infrared characterization of the planetary-mass companion ROXs 42B b
    We present new Keck/NIRC2 3-5 m infrared photometry of the planetary-mass companion to ROXS 42B in L', and for the first time in Brackett- (Brff) and in Ms-band. We combine our data with existing near-infrared photometry and K-band (2-2.4 m) spectroscopy and compare these data with models and other directly imaged planetary-mass objects using forward modeling and retrieval methods in order to characterize the atmosphere of ROXS 42B b. The ROXS 42B b 1.25-5 m spectral energy distribution most closely resembles that of GSC 06214 B and And b, although it has a slightly bluer Ks-Ms color than GSC 06214 B and thus currently lacks evidence of a circumplanetary disk. We cannot formally exclude the possibility that any of the tested dust-free/dusty/cloudy forward models describe the atmosphere of ROXS 42B b well. However, models with substantial atmospheric dust/clouds yield temperatures and gravities that are consistent when fit to photometry and spectra separately, whereas dust-free model fits to photometry predict temperatures/gravities inconsistent with the ROXS 42B b K-band spectrum and vice-versa. Atmospheric retrieval on the 1-5 m photometry places a limit on the fractional number density of CO2 of log (nCO2) < 2.7, but provides no other constraints so far. We conclude that ROXS 42B b has mid-IR photometric features that are systematically different from other previously observed planetary-mass and field objects of similar temperature. It remains unclear whether this is in the range of the natural diversity of targets at the very young ( 2 Myr) age of ROXS 42B b or unique to its early evolution and environment.
  102. Hanley, J., 2017, NatAs, 1, 0122, Titan: Bubbles in focus
    The seabed of Ligeia Mare, a hydrocarbon sea at the north pole of Titan, may be a favourable place for the separation of nitrogen and the creation of bubbles that then buoyantly rise to the sea's surface.
  103. Llama, J., Jardine, M., 2017, reph, 49, 200.06, 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.
  104. Pilyavsky, G., Mauskopf, P., Smith, N., et al., (including van Belle, G.), 2017, MNRAS, 467, 3048, Single-Photon Intensity Interferometry (SPIIFy): utilizing available telescopes
    One of the main scientific goals of optical interferometers is to measure the angular diameters of stars. These measurements, combined with precise distance measurements, such as those from the upcoming Gaia satellite, can provide improved constraints on stellar linear diameters and effective temperature. We describe a modular intensity interferometer system using commercially available single-photon detectors. We present our calculations on the sensitivity and uv-plane coverage using these modules mounted on existing telescopes on Kitt Peak, Arizona. Determining accurate stellar properties is important for testing models of stellar evolution as well as for deriving physical properties of transiting exoplanets. Our simulations indicate that we should be able to measure stellar diameters of bright stars with AB magnitude 6 with a precision of 5 per cent in a single night of observation.
  105. Benson, C., Scheeres, D., Moskovitz, N., 2017, spde, 117, Light-curves of Retired Geosynchronous Satellites
    Photometric light curve observations of several retired geosynchronous satellites are presented. These data were collected at Lowell Observatory in Flagstaff, Arizona during July 2016. Preliminary analysis of the light curves is conducted using Fourier series, Fourier transform, and phase folding methods to determine plausible rotation states. Satellites were found to have a variety of rotation states ranging from uniform to complex tumbling motion. For previously observed satellites, the potential for rotation state evolution is discussed. Analysis shows that two nearly identical weather satellites, GOES 8 and GOES 9, appear to be evolving quite differently. GOES 8 has progressed from uniform to increasingly complex tumbling motion since 2014 whereas the tumbling state of GOES 9 does not appear to have changed during this same span. Better understanding of the rotation state evolution of these retired geosynchronous satellites and others promises to improve estimates for attitude dependent solar radiation pressure forces, help assess potential for material shedding, and aid in on-orbit debris mitigation and recycling efforts.
  106. Noll, K., Buie, M., Grundy, W., et al., 2017, hst, 14928, Orbit of the Patroclus-Menoetius Binary, a Lucy Mission Target
    We are proposing to observe Trojan binary asteroid (617) Patroclus-Menoetius, one of the targets of the Lucy mission. Lucy was selected as the next Discovery mission on January 4, 2017, for launch in October 2021. Observations this year are needed to establish the mutual orbit of the binary, which is of critical importance for mission planning. The mutual orbit phase is essentially undetermined from the accumulation of orbit period uncertainty since last measured in 2010. Orbital phase is needed in order to be able to predict the timing of mutual events that will begin late in 2017. These mutual events are essential to planning for the Lucy mission, especially in establishing the precise orientation of the mutual orbit plane and ascending node that is critical to early planning for flyby encounter design and capabilities.
  107. Young, E., Klein, V., Hartig, K., et al., (including Wasserman, L.), 2017, EGUGA, 12164, Pluto's Haze from 2002 - 2015: Correlation with the Solar Cycle
    Occultations by Pluto were observed 2002, 2007, 2011 and 2015, with each event observed simultaneously in two or more wavelengths. Separate wavelengths allow us to discriminate between haze opacity and refractive effects due to an atmosphere's thermal profile - these two effects are notoriously hard to separate if only single-wavelength lightcurves are available. Of those four occultations, the amount of haze in Pluto's atmosphere was highest in 2002 (Elliot et al. 2003 report an optical depth of 0.11 at 0.73 m in the zenith direction), but undetectable in the 2007 and 2011 events (we find optical depth upper limits of 0.012 and 0.010 at 0.6 m). Cheng et al. (2016) report a zenith optical depth of 0.018 at 0.6 m from the haze profiles seen in New Horizons images. These four data points are correlated with the solar cycle. The 2002 haze detection occurred just after the peak of solar cycle 23, the 2007 and 2011 non-detections occurred during the solar minimum between peaks 23 and 24, and the New Horizons flyby took place just after the peak of solar cycle 24. This suggests that haze production on Pluto (a) is driven by solar UV photons or charged particles, (b) that sources and sinks on Pluto have timescales shorter than a few Earth years, and (c) the haze precursors on Pluto are not produced by Lyman-alpha radiation, because Lyman-alpha output only decreased by about one third in between the cycle 23 and 24 peaks, much less than the observed change in Pluto's haze abundances. References: Elliot, J.L. et al. (2003) Nature, Volume 424, Issue 6945, pp. 165-168.
  108. Maier, E., Elmegreen, B., Hunter, D., et al., (including Hollyday, G.), 2017, AJ, 153, 163, The Nature of Turbulence in the LITTLE THINGS Dwarf Irregular Galaxies
    We present probability density functions and higher order (skewness and kurtosis) analyses of the galaxy-wide and spatially resolved distributions of H I column density in the LITTLE THINGS sample of dwarf irregular galaxies. This analysis follows that of Burkhart et al. for the Small Magellanic Cloud (SMC). About 60% of our sample have galaxy-wide values of kurtosis that are similar to that found for the SMC, with a range up to much higher values, and kurtosis increases with integrated star formation rate. Kurtosis and skewness were calculated for radial annuli and for a grid of 32 pixel 32 pixel kernels across each galaxy. For most galaxies, kurtosis correlates with skewness. For about half of the galaxies, there is a trend of increasing kurtosis with radius. The range of kurtosis and skewness values is modeled by small variations in the Mach number close to the sonic limit and by conversion of H I to molecules at high column density. The maximum H I column densities decrease with increasing radius in a way that suggests molecules are forming in the weak-field limit, where H2 formation balances photodissociation in optically thin gas at the edges of clouds.
  109. Furlan, E., Ciardi, D., Everett, M., et al., (including Horch, E., van Belle, G.), 2017, AJ, 153, 201, Erratum: The Kepler Follow-up Observation Program. I. A Catalog of Companions to Kepler Stars from High-resolution Imaging (2017, AJ, 153, 71)
    No abstract found.
  110. Hunter, D., 2017, PASP, 129, 040201, Vera Cooper Rubin (1928-2016)
    No abstract found.
  111. Moskovitz, N., Polishook, D., DeMeo, F., et al., 2017, Icar, 284, 97, Near-infrared thermal emission from near-Earth asteroids: Aspect-dependent variability
    Here we explore a technique for constraining physical properties of near-Earth asteroids (NEAs) based on variability in thermal emission as a function of viewing aspect. We present case studies of the low albedo, near-Earth asteroids (285263) 1998 QE2 and (175706) 1996 FG3. The Near-Earth Asteroid Thermal Model (NEATM) is used to fit signatures of thermal emission in near-infrared (0.8 - 2.5 m) spectral data. This analysis represents a systematic study of thermal variability in the near-IR as a function of phase angle. The observations of QE2 imply that carefully timed observations from multiple viewing geometries can be used to constrain physical properties like retrograde versus prograde pole orientation and thermal inertia. The FG3 results are more ambiguous with detected thermal variability possibly due to systematic issues with NEATM, an unexpected prograde rotation state, or a surface that is spectrally and thermally heterogenous. This study highlights the potential diagnostic importance of high phase angle thermal measurements on both sides of opposition. We find that the NEATM thermal beaming parameters derived from our near-IR data tend to be of order10's of percent higher than parameters from ensemble analyses of longer wavelength data sets. However, a systematic comparison of NEATM applied to data in different wavelength regimes is needed to understand whether this offset is simply a reflection of small number statistics or an intrinsic limitation of NEATM when applied to near-IR data. With the small sample presented here, it remains unclear whether NEATM modeling at near-IR wavelengths can robustly determine physical properties like pole orientation and thermal inertia.
  112. Holler, B., Young, L., Buie, M., et al., (including Grundy, W., Roe, H.), 2017, Icar, 284, 394, Measuring temperature and ammonia hydrate ice on Charon in 2015 from Keck/OSIRIS spectra
    In this work we investigated the longitudinal (zonal) variability of H2O and ammonia (NH3) hydrate ices on the surface of Charon through analysis of the 1.65 m and 2.21 mabsorption features, respectively. Near-infrared spectra presented here were obtained between 2015-07-14 and 2015-08-30 UT with the OSIRIS integral field spectrograph on Keck I. Spectra centered on six different sub-observer longitudes were obtained through the Hbb (1.473-1.803 m) and Kbb (1.965-2.381 m) filters. Gaussian functions were fit to the aforementioned bands to obtain information on band center, band depth, full width at half maximum, and band area. The shift in the band center of the temperature-dependent 1.65 m feature was used to calculate the H2O ice temperature. The mean temperature of the ice on the observable portion of Charon's surface is 45 14 K and we report no statistically significant variations in temperature across the surface. We hypothesize that the crystalline and amorphous phases of water ice reached equilibrium over 3.5 Gyr ago, with thermal recrystallization balancing the effects of irradiation amorphization. We do not believe that cryovolcanism is necessary to explain the presence of crystalline water ice on the surface of Charon. Absorption from ammonia species is detected between 12 and 290, in agreement with results from New Horizons. Ongoing diffusion of ammonia through the rocky mantle and upper layer of water ice is one possible mechanism for maintaining its presence in Charon's surface ice. Reduced Charon spectra corrected for telluric and solar absorption are available as supplementary online material.
  113. Martin, E., Mace, G., McLean, I., et al., (including Prato, L.), 2017, ApJ, 838, 73, Surface Gravities for 228 M, L, and T Dwarfs in the NIRSPEC Brown Dwarf Spectroscopic Survey
    We combine 131 new medium-resolution (R 2000) J-band spectra of M, L, and T dwarfs from the Keck NIRSPEC Brown Dwarf Spectroscopic Survey (BDSS) with 97 previously published BDSS spectra to study surface-gravity-sensitive indices for 228 low-mass stars and brown dwarfs spanning spectral types M5-T9. Specifically, we use an established set of spectral indices to determine surface gravity classifications for all of the M6-L7 objects in our sample by measuring the equivalent widths (EW) of the K I lines at 1.1692, 1.1778, and 1.2529 m, and the 1.2 m FeH J absorption index. Our results are consistent with previous surface gravity measurements, showing a distinct double peakat L5 and T5in K I EW as a function of spectral type. We analyze the K I EWs of 73 objects of known ages and find a linear trend between log(Age) and EW. From this relationship, we assign age ranges to the very low gravity, intermediate gravity, and field gravity designations for spectral types M6-L0. Interestingly, the ages probed by these designations remain broad, change with spectral type, and depend on the gravity-sensitive index used. Gravity designations are useful indicators of the possibility of youth, but current data sets cannot be used to provide a precise age estimate.

    The data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation.

  114. Wang, J., Prato, L., Mawet, D., 2017, ApJ, 838, 35, Time-resolved High Spectral Resolution Observation of 2MASSW J0746425+200032AB
    Many brown dwarfs (BDs) exhibit photometric variability at levels from tenths to tens of percents. The photometric variability is related to magnetic activity or patchy cloud coverage, characteristic of BDs near the L-T transition. Time-resolved spectral monitoring of BDs provides diagnostics of cloud distribution and condensate properties. However, current time-resolved spectral studies of BDs are limited to low spectral resolution (R 100) with the exception of the study of Luhman 16 AB at a resolution of 100,000 using the VLT+CRIRES. This work yielded the first map of BD surface inhomogeneity, highlighting the importance and unique contribution of high spectral resolution observations. Here, we report on the time-resolved high spectral resolution observations of a nearby BD binary, 2MASSW J0746425+200032AB. We find no coherent spectral variability that is modulated with rotation. Based on simulations, we conclude that the coverage of a single spot on 2MASSW J0746425+200032AB is smaller than 1% or 6.25% if spot contrast is 50% or 80% of its surrounding flux, respectively. Future high spectral resolution observations aided by adaptive optics systems can put tighter constraints on the spectral variability of 2MASSW J0746425+200032AB and other nearby BDs.
  115. Rubio, M., Elmegreen, B., Hunter, D., et al., 2017, IAUS, 321, 229, Dense Cloud Cores revealed by ALMA CO observations in the low metallicity dwarf galaxy WLM
    Understanding stellar birth requires observations of the clouds in which they form. These clouds are dense and self-gravitating, and in all existing observations, they are molecular with H2 the dominant species and CO the best available. When the abundances of carbon and oxygen are low compared to hydrogen, and the opacity from dust is also low, as in primeval galaxies and local dwarf irregular galaxies CO forms slowly and is easily destroyed, so it cannot accumulate inside dense clouds. Then we lose our ability to trace the gas in regions of star formation and we lose critical information on the temperatures, densities, and velocities of the material that collapses. I will report on high resolution observations with ALMA of CO clouds in the local group dwarf irregular galaxy WLM, which has a metallicity that is 13% of the solar value and 50% lower than the previous CO detection threshold and the properties derived of very small dense CO clouds mapped..
  116. Hillwig, T., Jacoby, G., Jones, D., et al., 2017, ASPC, 509, 469, Binarity in the Central Stars of Planetary Nebulae and its Relationship to Stellar Evolution: An Observational Perspective
    The existing status of our knowledge of binary central stars of planetary nebulae will be explored. Binary modeling of known systems is providing physical parameters that can be compared amongst the sample, with nebular characteristics, and with similar binaries with no associated planetary nebula. Correlations among these areas will be discussed, especially in relation to our understanding of stellar evolution.
  117. Oszkiewicz, D., Skiff, B., Moskovitz, N., et al., (including Marciniak, A.), 2017, A&A, 599, A107, Non-Vestoid candidate asteroids in the inner main belt
    Context. Most howardite-eucrite-diogenite (HED) meteorites (analogues to V-type asteroids) are thought to originate from the asteroid (4) Vesta. However some HEDs show distinct oxygen isotope ratios and therefore are thought to originate from other asteroids. In this study we try to identify asteroids that may represent parent bodies of those mismatching HEDs.
    Aims: The main goal of this study is to test the hypothesis that there might be V-type asteroids in the inner main asteroid belt unrelated to (4) Vesta. In order to evolve outside the Vesta family and became Vesta fugitives, asteroids should produce the correct Yarkovsky drift. The direction of which is dependent on asteroid sense of rotation. Therefore we focus on determining sense of rotation for asteroids outside the Vesta family to better understand their origin.
    Methods: We performed photometric observations using the 1.1 m and 1.8 m telescopes at Lowell Observatory to determine rotational synodic periods of selected objects before, at, and after opposition. Prograde rotators show a minimum in synodic period at opposition while retrograde rotators show a maximum. This is known as the "drifting minima" method. Changes in the rotational period are on the order of seconds and fractions of seconds and depend on the rotational pole of the object and the asteroid-observer-Sun geometry at opposition.
    Results: We have determined sense of rotation for eight asteroids and retrieved spin states for three objects from literature. For one asteroid we were not able to determine the sense of rotation. In total our sample includes 11 V-type asteroids and one S-type (test object). We have revised rotation periods for three objects. Five V-types in our sample can be explained by migration from the Vesta family. Two show spin states that are inconsistent with migration from Vesta. The origin of the remaining objects is ambiguous.
    Conclusions: We found two objects with rotations inconsistent with migration from Vesta. Assuming that the YORP effect and random collisions did not substantially modify their sense of rotation, those objects are candidates for non-Vestoids in the inner asteroid belt. Finding more non-Vestoids is crucial in testing the formation and migration theory of differentiated parent bodies.
  118. Massey, P., Neugent, K., Morrell, N., 2017, ApJ, 837, 122, A Modern Search for Wolf-Rayet Stars in the Magellanic Clouds. III. A Third Year of Discoveries
    For the past three years we have been conducting a survey for Wolf-Rayet (WR) stars in the Large and Small Magellanic Clouds (LMC, SMC). Our previous work resulted in the discovery of a new type of WR star in the LMC, which we are calling WN3/O3. These stars have the emission-line properties of a WN3 star (strong N v, but no N IV), plus the absorption-line properties of an O3 star (Balmer hydrogen plus Pickering He II, but no He I). Yet, these stars are 15 times fainter than an O3 V star, ruling out the possibility that WN3/O3s are WN3+O3 binaries. Here we report the discovery of two more members of this class, bringing the total number of these objects to 10, 6.5% of the LMCs total WR population. The optical spectra of nine of these WN3/O3s are virtually indistinguishable from each other, but one of the newly found stars is significantly different, showing a lower excitation emission and absorption spectrum (WN4/O4-ish). In addition, we have newly classified three unusual Of-type stars, including one with a strong C III 4650 line, and two rapidly rotating Oef stars. We also rediscovered a low mass X-ray binary, RX J0513.9-6951, and demonstrate its spectral variability. Finally, we discuss the spectra of 10 low priority WR candidates that turned out to not have He II emission. These include both a Be star and a B[e] star.

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

  119. Furlan, E., Ciardi, D., Everett, M., et al., (including Horch, E., van Belle, G.), 2017, AJ, 153, 71, The Kepler Follow-up Observation Program. I. A Catalog of Companions to Kepler Stars from High-Resolution Imaging
    We present results from high-resolution, optical to near-IR imaging of host stars of Kepler Objects of Interest (KOIs), identified in the original Kepler field. Part of the data were obtained under the Kepler imaging follow-up observation program over six years (2009-2015). Almost 90% of stars that are hosts to planet candidates or confirmed planets were observed. We combine measurements of companions to KOI host stars from different bands to create a comprehensive catalog of projected separations, position angles, and magnitude differences for all detected companion stars (some of which may not be bound). Our compilation includes 2297 companions around 1903 primary stars. From high-resolution imaging, we find that 10% (30%) of the observed stars have at least one companion detected within 1 (4). The true fraction of systems with close (4) companions is larger than the observed one due to the limited sensitivities of the imaging data. We derive correction factors for planet radii caused by the dilution of the transit depth: assuming that planets orbit the primary stars or the brightest companion stars, the average correction factors are 1.06 and 3.09, respectively. The true effect of transit dilution lies in between these two cases and varies with each system. Applying these factors to planet radii decreases the number of KOI planets with radii smaller than 2 {R}\oplus by 2%-23% and thus affects planet occurrence rates. This effect will also be important for the yield of small planets from future transit missions such as TESS.
  120. Jacoby, G., De Marco, O., Davies, J., et al., 2017, ApJ, 836, 93, Masses of the Planetary Nebula Central Stars in the Galactic Globular Cluster System from HST Imaging and Spectroscopy
    The globular cluster (GC) system of our Galaxy contains four planetary nebulae (PNe): K 648 (or Ps 1) in M15, IRAS 18333-2357 in M22, JaFu 1 in Pal 6, and JaFu 2 in NGC 6441. Because single-star evolution at the low stellar mass of present-epoch GCs was considered incapable of producing visible PNe, their origin presented a puzzle. We imaged the PN JaFu 1 with the Hubble Space Telescope (HST) to obtain photometry of its central star (CS) and high-resolution morphological information. We imaged IRAS 18333-2357 with better depth and resolution, and we analyzed its archival HST spectra to constrain its CS temperature and luminosity. All PNe in Galactic GCs now have quality HST data, allowing us to improve CS mass estimates. We find reasonably consistent masses between 0.53 and 0.58 M for all four objects, though estimates vary when adopting different stellar evolutionary calculations. The CS mass of IRAS 18333-2357, though, depends strongly on its temperature, which remains elusive due to reddening uncertainties. For all four objects, we consider their CS and nebula masses, their morphologies, and other incongruities to assess the likelihood that these objects formed from binary stars. Although generally limited by uncertainties (0.02 M ) in post-AGB tracks and core mass versus luminosity relations, the high-mass CS in K 648 indicates a binary origin. The CS of JaFu 1 exhibits compact, bright [O III] and H emission, like EGB 6, suggesting a binary companion or disk. Evidence is weaker for a binary origin of JaFu 2.

    Based, in part, on observations made with the NASA/ESA Hubble Space Telescope, obtained [from the Data Archive] at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program GO-11558.

  121. Johnson, M., Hunter, D., Kamphuis, P., et al., 2017, MNRAS, 465, L49, A constant intrinsic thickness for dwarf irregular galaxies?
    We assess the intrinsic thickness parameter, qo, for a sample of dwarf irregular galaxies and compare to larger, more massive spiral galaxy systems. We use optical photometry to determine b/a (minor-to-major axial ratio), and we use the H I kinematic inclination angle to derive qo. We find that qo ranges from 0.1 to 0.8 for the dwarfs. We find a trend in qo with luminosity, indicating that fainter dwarfs are thicker than brighter ones, similar to previous studies. However, we also find a trend in qo with H I kinematic inclination, which indicates that either the radius at which we measure b/a may be too small, or, that the stellar and gas discs have different inclinations. Because we selected only those objects that have nearly identical morphological and kinematic position angles, we find the latter reason unlikely. We find a weak trend in qo with hz/RD (ratio of stellar scaleheight to scalelength), which points to b/a not fully representing the stellar disc distribution. We conclude that a constant qo may not be appropriate for dwarf irregulars.
  122. Vokrouhlicky, D., Pravec, P., Durech, J., et al., (including Moskovitz, N., Thirouin, A.), 2017, A&A, 598, A91, The young Datura asteroid family. Spins, shapes, and population estimate
    Context. Asteroid families are the outcomes of disruption or cratering events on a size and energy scales that are not reproducible in laboratory experiments. Overall structure, as well as properties of individual members, in the old families could have been changed since their formation. Therefore young families preserve best the characteristics of the initial event.
    Aims: We study the most suitable known asteroid family with an age of less than 1 Myr, the Datura family. We aim (I) to obtain information about rotation state and shape of the largest members in the family; and (II) to constrain its debiased population down to couple of hundreds of meters in size.
    Methods: We have analyzed the up-to-date catalog of orbital elements of main belt asteroids. We evaluated the detection efficiency of Catalina Sky Survey (CSS) in regard to detections of members in the Datura family, and we have used our photometric observations and lightcurve inversion methods to determine the rotation states and shapes of the largest members of the family.
    Results: We determined rotation periods of the seven largest members of the Datura family, and we also derived accurate mean absolute magnitudes for six of them. Except for the largest fragment (1270) Datura, the asteroids tend to have long rotation periods and large amplitude of the lightcurve, witnessing an elongated shape. For the four largest asteroids, our observations allow us to resolve rotation pole and a rough shape. All of them are prograde-rotating and have the latitude of the rotation pole >50. Our search in orbital catalogs resulted in the discovery of many small, sub-kilometer members of the Datura family. Using the CSS detection efficiency, we inverted this information into the debiased population of Datura family members. We show that the mass and angular momentum content in small fragments is negligible compared to the largest fragment (1270) Datura. These findings may help to constrain the formation mechanism of the family.
  123. Kane, S., von Braun, K., Henry, G., et al., 2017, ApJ, 835, 200, Characterization of the Wolf 1061 Planetary System
    A critical component of exoplanetary studies is an exhaustive characterization of the host star, from which the planetary properties are frequently derived. Of particular value are the radius, temperature, and luminosity, which are key stellar parameters for studies of transit and habitability science. Here we present the results of new observations of Wolf 1061, known to host three super-Earths. Our observations from the Center for High Angular Resolution Astronomy interferometric array provide a direct stellar radius measurement of 0.3207 0.0088 R, from which we calculate the effective temperature and luminosity using spectral energy distribution models. We obtained 7 yr of precise, automated photometry that reveals the correct stellar rotation period of 89.3 1.8 days, finds no evidence of photometric transits, and confirms that the radial velocity signals are not due to stellar activity. Finally, our stellar properties are used to calculate the extent of the Habitable Zone (HZ) for the Wolf 1061 system, for which the optimistic boundaries are 0.09-0.23 au. Our simulations of the planetary orbital dynamics show that the eccentricity of the HZ planet oscillates to values as high as 0.15 as it exchanges angular momentum with the other planets in the system.
  124. Yee, S., Petigura, E., von Braun, K., 2017, ApJ, 836, 77, Precision Stellar Characterization of FGKM Stars using an Empirical Spectral Library
    Classification of stars, by comparing their optical spectra to a few dozen spectral standards, has been a workhorse of observational astronomy for more than a century. Here, we extend this technique by compiling a library of optical spectra of 404 touchstone stars observed with Keck/HIRES by the California Planet Search. The spectra have high resolution (R 60,000), high signal-to-noise ratio (S/N 150/pixel), and are registered onto a common wavelength scale. The library stars have properties derived from interferometry, asteroseismology, LTE spectral synthesis, and spectrophotometry. To address a lack of well-characterized late-K dwarfs in the literature, we measure stellar radii and temperatures for 23 nearby K dwarfs, using modeling of the spectral energy distribution and Gaia parallaxes. This library represents a uniform data set spanning the spectral types M5-F1 (T eff 3000-7000 K, R 0.1-16 R ). We also present Empirical SpecMatch (SpecMatch-Emp), a tool for parameterizing unknown spectra by comparing them against our spectral library. For FGKM stars, SpecMatch-Emp achieves accuracies of 100 K in effective temperature (T eff), 15% in stellar radius (R ), and 0.09 dex in metallicity ([Fe/H]). Because the code relies on empirical spectra it performs particularly well for stars K4 and later, which are challenging to model with existing spectral synthesizers, reaching accuracies of 70 K in T eff, 10% in R , and 0.12 dex in [Fe/H]. We also validate the performance of SpecMatch-Emp, finding it to be robust at lower spectral resolution and S/N, enabling the characterization of faint late-type stars. Both the library and stellar characterization code are publicly available.
  125. Garcia, E., Currie, T., Guyon, O., et al., 2017, ApJ, 834, 162, SCExAO and GPI Y JHBand Photometry and Integral Field Spectroscopy of the Young Brown Dwarf Companion to HD 1160
    We present high signal-to-noise ratio, precise Y JH photometry and Y band (0.957-1.120 m) spectroscopy of HD 1160 B, a young substellar companion discovered from the Gemini NICI Planet Finding Campaign using the Subaru Coronagraphic Extreme Adaptive Optics instrument and the Gemini Planet Imager. HD 1160 B has typical mid-M dwarf-like infrared colors and a spectral type of M5.5{}-0.5+1.0, where the blue edge of our Y band spectrum rules out earlier spectral types. Atmospheric modeling suggests HD 1160 B has an effective temperature of 3000-3100 K, a surface gravity of log g = 4-4.5, a radius of 1.55 0.10 RJ, and a luminosity of log L/L = -2.76 0.05. Neither the primarys Hertzspring-Russell diagram position nor atmospheric modeling of HD 1160 B show evidence for a subsolar metallicity. Interpretation of the HD 1160 B spectroscopy depends on which stellar system components are used to estimate the age. Considering HD 1160 A, B and C jointly, we derive an age of 80-125 Myr, implying that HD 1160 B straddles the hydrogen-burning limit (70-90 MJ). If we consider HD 1160 A alone, younger ages (20-125 Myr) and a brown dwarf-like mass (35-90 MJ) are possible. Interferometric measurements of the primary, a precise Gaia parallax, and moderate-resolution spectroscopy can better constrain the systems age and how HD 1160 B fits within the context of (sub)stellar evolution.
  126. Egeland, R., Soon, W., Baliunas, S., et al., (including Hall, J.), 2017, ApJ, 835, 25, The Mount Wilson Observatory S-index of the Sun
    The most commonly used index of stellar magnetic activity is the instrumental flux scale of singly ionized calcium H & K line core emission, S, developed by the Mount Wilson Observatory (MWO) HK Project, or the derivative index {R}{HK}\prime . Accurately placing the Sun on the S scale is important for comparing solar activity to that of the Sun-like stars. We present previously unpublished measurements of the reflected sunlight from the Moon using the second-generation MWO HK photometer during solar cycle 23 and determine cycle minimum {S}23,\min =0.1634+/- 0.0008, amplitude {{ }}{S}23=0.0143+/- 0.0012, and mean < {S}23> =0.1701+/- 0.0005. By establishing a proxy relationship with the closely related National Solar Observatory Sacramento Peak calcium K emission index, itself well correlated with the Kodaikanal Observatory plage index, we extend the MWO S time series to cover cycles 15-24 and find on average < {S}\min > =0.1621+/- 0.0008, < {{ }}{S}{cyc}> =0.0145+/- 0.0012, < {S}{cyc}> =0.1694+/- 0.0005. Our measurements represent an improvement over previous estimates that relied on stellar measurements or solar proxies with non-overlapping time series. We find good agreement from these results with measurements by the Solar-Stellar Spectrograph at Lowell Observatory, an independently calibrated instrument, which gives us additional confidence that we have accurately placed the Sun on the S-index flux scale.
  127. Swihart, S., Garcia, E., Stassun, K., et al., (including van Belle, G.), 2017, AJ, 153, 16, A Catalog of Calibrator Stars for Next-generation Optical Interferometers
    Benchmark stars with known angular diameters are key to calibrating interferometric observations. With the advent of optical interferometry, there is a need for suitably bright, well-vetted calibrator stars over a large portion of the sky. We present a catalog of uniformly computed angular diameters for 1510 stars in the northern hemisphere, brighter than V = 6 and with declinations -15^\circ < < 82^\circ . The median angular stellar diameter is 0.529 mas. The list has been carefully cleansed of all known binary and multiple stellar systems. We derive the angular diameters for each of the stars by fitting spectral templates to the observed spectral energy distributions (SEDs) from literature fluxes. We compare these derived angular diameters against those measured by optical interferometry for 75 of the stars, as well as to 176 diameter estimates from previous calibrator catalogs, finding in general excellent agreement. The final catalog includes our goodness-of-fit metrics as well as an online atlas of our SED fits. The catalog presented here permits selection of the best calibrator stars for current and future visible-light interferometric observations.
  128. Hunter, D., Ficut-Vicas, D., Ashley, T., et al., (including Herrmann, K., Johnson, M., Zhang, H.), 2017, AJ, 153, 47, Erratum: "Little Things" (2012, AJ, 144, 134)
    No abstract found.
  129. Hunter, D., Elmegreen, B., Gehret, E., 2017, AJ, 153, 48, Erratum: Young Star Clusters in the Outer Disks of LITTLE THINGS Dwarf Irregular Galaxies (2016, AJ, 151, 136)
    No abstract found.
  130. West, M., Gregg, M., Toller, J., 2017, AAS, 229, 105.04, The Cluster Environments of Quasar Groups
    Quasars are rare astronomical objects, and quasar pairs, triplets and larger groupings are even rarer. The presence of several quasars in the same small volume of space might therefore indicate a region that is exceptionally rich in galaxies, and hence groups of quasars could serve as ueful beacons for identifying distant clusters or protoclusters of galaxies. With this motivation, we compare the cluster environments of single versus multiple quasar systems using data from the Sloan Digital Sky Survey.
  131. Hall, J., 2017, AAS, 229, 126.01, Lowell Observatory's Discovery Channel Telescope
    Lowell Observatory broke ground on its 4.3-meter Discovery Channel Telescope (DCT) in July 2005 and celebrated first light for the telescope in July 2012. In this overview to this special session, I will discuss the origin and development of the project, the telescope's general specifications and performance, its current operating status, and the initial instrument suite.
  132. Prato, L., 2017, AAS, 229, 126.06, IGRINS on the DCT
    Through an agreement with the University of Texas at Austin and the Korea Astronomy and Space Science Institute, the Immersion Grating Infrared Spectrograph (IGRINS) saw first light on the Lowell Observatory 4.3 m Discovery Channel Telescope (DCT) telescope on September 8, 2016. IGRINS, originally commissioned at the McDonald Observatory 2.7 m telescope, provides a spectral resolution of 45,000 and a simultaneous spectral grasp of 1.45 to 2.45 microns, recording all of the H and K bands with no gaps in wavelength coverage on two H2RG detectors in a single exposure. The instrument design minimizes optical surfaces, optimizing throughput, and has no moving parts, key for stability. IGRINS on the DCT attains a signal to noise of 100 per resolution element in one hour of integration time on a K=12 magnitude source, currently making it the most sensitive high-resolution spectrograph in the world at H and K. Science programs in the fourth quarter, 2016, include such diverse topics as abundance measurements in M dwarfs and population II stars, studies of ices and atmospheres in outer solar system bodies, measurement of fundamental properties of pre-main sequence stars, calibrating young star evolution, defining the substellar boundary at the youngest ages, outflow characteristics in Wolf-Rayet stars, finding the first generation of exoplanets, gas dynamics in planetary nebulae, and structure of the ISM in molecular clouds. In this talk I will report on initial results from selected programs.
  133. van Belle, G., Horch, E., 2017, AAS, 229, 126.09, Speckle Interferometry at Lowell's Discovery Channel Telescope
    The high-spatial-resolution technique of speckle interferometry has been in use at Lowell Observatory's Discovery Channel Telescope since 2014 with the Dual-channel Stellar Speckle Imager (DSSI; Horch et al. 2009) as a visiting instrument. Using its standard bandpasses of 692 and 880nm, we have used highly efficient DSSI instrument to inspect over a thousand stellar systems over the course of 2014 (Horch et al. 2015). We have also demonstrated the usefulness of the DSSI@DCT system for resolved observations of high-altitude (>1,000 miles) man-made satellites in highly non-sidereal rate orbits.
  134. Herrmann, K., Hunter, D., Zhang, H., et al., 2017, AAS, 229, 145.22, Mass-to-Light versus Color Relations for Dwarf Irregular Galaxies
    We have determined new relations between UBV colors and mass-to-light (M/L) ratios for dwarf irregular galaxies, as well as for transformed g - r. These M/L to color relations (MLCRs) are based on stellar mass density profiles determined for 34 LITTLE THINGS dwarfs from spectral energy distribution fitting to multi-wavelength surface photometry in passbands from the FUV to the NIR. These relations can be used to determine stellar masses in dwarf irregular galaxies for situations where other determinations of stellar mass are not possible. Our MLCRs are shallower than comparable MLCRs in the literature determined for spiral galaxies. We divided our dwarf data into four metallicity bins and found indications of a steepening of the MLCR with increased oxygen abundance, perhaps due to more line blanketing occurring at higher metallicity.
  135. Gallardo, S., Hunter, D., LEGUS Team, 2017, AAS, 229, 145.26, Comparison between high and low star forming sides of dwarf irregular galaxies with asymmetrical distributions of star formation.
    Dwarf irregular galaxies DDO 187 and NGC 3738, in the LITTLE THINGS sample of nearby dwarfs, share the similar characteristic of having more star formation on one side of the galaxy than the other. I compared characteristics of the galaxies, such as pressure, HI surface density, and stellar mass surface density, measured on the high star formation half with those measured on the low star formation half. Comparing the galaxies, we see that the ratios of galactic properties from the high star formation side to the low star formation side are similar in both galaxies. We also see that the high star formation halves of the galaxies have higher pressure, higher stellar mass density, and higher gas mass density. Both galaxies also have peculiar gas kinematics. Looking at the young star clusters in NGC 3738 from the LEGUS survey, we see that there are younger and more clusters in the high star formation region. The cause of having such an asymmetrical distribution of star formation in these galaxies remains unknown.SG appreciates the funding to Northern Arizona University for the Research Experiences for Undergraduates program in the form of grant AST-1461200 from NSF. DAH is grateful for grant HST-GO-13364.022-A for participation in LEGUS.
  136. Rilinger, A., Kwitter, K., Balick, B., et al., (including Jacoby, G.), 2017, AAS, 229, 148.09, Spectroscopy of Planetary Nebulae at the Bright End of the Luminosity Function
    We have obtained spectra of 8 luminous planetary nebulae (PNe) in M31 and 4 in the Large Magellanic Cloud with the goal of understanding their properties and those of their progenitor stars. These PNe are at or near the M* region (the most luminous PNe) in their respective galaxies. M31 PNe were observed at the Gran Telescopio Canarias using the OSIRIS spectrograph; LMC PNe were observed with the FORS2 spectrograph at the Very Large Telescope. Line intensities were measured in IRAF. Using our n-level atom program, ELSA (Johnson, et.al, 2006, Planetary Nebulae in our Galaxy and Beyond, 234, 439), we determined temperature, density, and elemental abundances for each nebula. We then modeled the nebulae and central stars with Cloudy (Ferland, et al. 1998, PASP, 110, 761). We plan to use these models of the central stars to estimate the masses and ages of the progenitor stars. We hope to discover whether the progenitor stars of M* PNe exhibit consistently different characteristics from those of other PNe progenitors.
  137. Evans, K., Massey, P., 2017, AAS, 229, 154.04, The Red Supergiant Content of the LMC and SMC
    We have investigated the red supergiant (RSG) population of the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) through a radial velocity survey of 309 candidate RSGs in the LMC and 356 in the SMC, confirming the presence of 304 RSG in the LMC and 316 in the SMC. Using these spectra, we have measured effective temperatures and spectral types for each confirmed RSG. These data allow us to compare our sample of stars with the Geneva model evolutionary tracks. This work has been partially supported by the National Science Foundation AST-1612874.
  138. Jacoby, G., Bida, T., Fischer, D., et al., (including Massey, P., Roe, H., Prato, L.), 2017, AAS, 229, 155.02, Instruments at the Lowell Observatory Discovery Channel Telescope (DCT)
    The Lowell Observatory Discovery Channel Telescope (DCT) has been in full science operation for 2 years (2015 and 2016). Five instruments have been commissioned during that period, and two additional instruments are planned for 2017. These include:+ Large Monolithic Imager (LMI) - a CCD imager (12.6 arcmin FoV)+ DeVeny - a general purpose optical spectrograph (2 arcmin slit length, 10 grating choices)+ NIHTS - a low resolution (R=160) YJHK spectrograph (1.3 arcmin slit)+ DSSI - a two-channel optical speckle imager (5 arcsec FoV)+ IGRINS - a high resolution (45,000) HK spectrograph, on loan from the University of Texas.In the upcoming year, instruments will be delivered from the University of Maryland (RIMAS - a YJHK imager/spectrograph) and from Yale University (EXPRES - a very high resolution stabilized optical echelle for PRV).Each of these instruments will be described, along with their primary science goals.
  139. Dupuy, T., Kraus, A., Kratter, K., et al., (including Prato, L.), 2017, AAS, 229, 219.01, Orbital Architectures of Planet-Hosting Binaries: Testing Co-alignment
    Most planetary system only offer the possibility to measure the initial conditions of planet formation (e.g., protoplanetary disks) separately from the final outcome (e.g., planet demographics of field samples). Planet-hosting binaries offer the rare opportunity to observe both simultaneously. For example, in our previous work on the hierarchical triple system Kepler-444 that hosts five Mars-sized planets, we demonstrated that the present-day stellar orbits imply that the planets must have formed from a protoplanetary disk that was truncated at 1-2 AU. Here we will present new results from our continuing Keck adaptive optics program to monitor the stellar orbits of Kepler planet hosts that have binary companions at solar-system scales of 20-100 AU. The astrometric orbital arcs that we measure enable a fundamental test: whether or not the stellar orbits are seen edge-on and thus co-aligned with the transiting planets in the system. This orbit-orbit alignment test allows us to critically examine the possible formation pathways for these systems, thereby providing key insights into planet formation models that have been proposed to explain the origins of Kepler planets. We will also discuss preliminary results for a subset of our sample for which we have obtained resolved radial velocities with NIRSPAO that allow us to measure additional orbit parameters (eccentricity and semimajor axis). Full orbit determinations will allow us to address whether special conditions (e.g., circular orbits) are preferred for forming planets in binaries, which are the most common type of stellar system in the Galaxy.
  140. van Belle, G., von Braun, K., Ciardi, D., et al., 2017, AAS, 229, 240.28, The PTI Giant Star Angular Size Survey: Effective Temperatures & Linear Radii
    We report new interferometric angular diameter observations of over 200 giant stars observed with the Palomar Testbed Interferometer (PTI). These angular diameters are combined with bolometric fluxes derived from detailed spectral energy distribution (SED) fits, to produce robust estimates of effective temperature (T_EFF). These SED fits include reddening estimates and are based upon fits of empirical spectral templates to literature photometry, and narrow-band photometry obtained at the Lowell 31" telescope. The 58 nights of 31" observing have produced over 45,000 new photometric data points on these stars, allowing for flux and reddening determination with unprecident precision. Over the range from G5III to M8III, T_EFF estimates are precise to 50K per spectral type. For the 87 objects in Gaia DR1, radius estimates are improved over the Hipparcos estimates (van Leeuwen 2007) but only by a factor of 1.7 reduction in error, and are typically ~6% per star.
  141. Prato, L., Avilez, I., Allen, T., et al., (including Zoonematkermani, S., Biddle, L., Muzzio, R., Wittal, M.), 2017, AAS, 229, 241.02, The Young Visual Binary Database
    We have obtained adaptive optics imaging and high-resolution H-band and in some cases K-band spectra of each component in close to 100 young multiple systems in the nearby star forming regions of Taurus, Ophiuchus, TW Hya, and Orion. The binary separations for the pairs in our sample range from 30 mas to 3 arcseconds. The imaging and most of our spectra were obtained with instruments behind adaptive optics systems in order to resolve even the closest companions. We are in the process of determining fundamental stellar and circumstellar properties, such as effective temperature, Vsin(i), veiling, and radial velocity, for each component in the entire sample. The beta version of our database includes systems in the Taurus region and provides plots, downloadable ascii spectra, and values of the stellar and circumstellar properties for both stars in each system. This resource is openly available to the community at http://jumar.lowell.edu/BinaryStars/. In this poster we describe initial results from our analysis of the survey data. Support for this research was provided in part by NSF award AST-1313399 and by NASA Keck KPDA funding.
  142. Muzzio, R., Avilez, I., Prato, L., et al., (including Allen, T., Wright-Garba, N.), 2017, AAS, 229, 241.03, Effective Temperatures for Young Stars in Binaries
    We have observed about 100 multi-star systems, within the star forming regions Taurus and Ophiuchus, to investigate the individual stellar and circumstellar properties of both components in young T Tauri binaries. Near-infrared spectra were collected using the Keck II telescopes NIRSPEC spectrograph and imaging data were taken with Keck IIs NIRC2 camera, both behind adaptive optics. Some properties are straightforward to measure; however, determining effective temperature is challenging as the standard method of estimating spectral type and relating spectral type to effective temperature can be subjective and unreliable. We explicitly looked for a relationship between effective temperatures empirically determined in Mann et al. (2015) and equivalent width ratios of H-band Fe and OH lines for main sequence spectral type templates common to both our infrared observations and to the sample of Mann et al. We find a fit for a wide range of temperatures and are currently testing the validity of using this method as a way to determine effective temperature robustly. Support for this research was provided by an REU supplement to NSF award AST-1313399.
  143. Avilez, I., Prato, L., Allen, T., et al., (including Wright-Garba, N., Biddle, L., Muzzio, R.), 2017, AAS, 229, 241.04, Variable Stellar and Circumstellar Properties of the Young Binary VV CrA
    VV CrA is a 2 arcsecond young binary system in the Corona Australis star forming region. The NE component, fainter in the near-infrared and invisible at optical wavelengths, dominates in the thermal infrared. The system has drawn attention because of its high degree of variability, significant cicrumstellar emission, and the mysterious nature of the infrared companion. Using high-resolution H- and K-band spectroscopy taken with the NIRSPEC spectrometer at the 10 m Keck II telescope, we have for the first time determined the spectral types of both components: the optically dominant primary is an M0 and the infrared compaion is an earlier K7 type star. Both components show significant and variable levels of H-band veiling, observed over 4 to 5 epochs during a period of 4 years; at times the veiling almost completely obscures the photospheric absorption lines. Hydrogen emission lines are observed at both H (Brackett 16) and K (Brackett gamma), consistent with the high rates of mass accretion described in previous studies. We determine values of Vsin(i), effective temperature, veiling, and radial velocity for both components and describe these results in the context of models of the nature and orientation of the system proposed by Smith et al. (2009) and Scicluna et al. (2016). The geometry of the VV CrA system may present a unique opportunity to study not only young star evolution in the binary environment but also to explore cirumstellar disk structure in high detail.Support for this research was provided by an REU supplement to NSF award AST-1313399.
  144. Wittal, M., Prato, L., Schaefer, G., et al., (including Thomas, A., Biddle, L., Avilez, I., Muzzio, R.), 2017, AAS, 229, 241.06, Is the Young UY Auriga System a Triple?
    In an effort to understand the nature of the young binary, UY Aur, we examined the variable behavior of the entire, unresolved 0.9 arcsecond system, as well as the behavior of the angularly resolved, individual A and B components. UY Aur is an approximately 2 Myr old, classical T Tauri in the Taurus-Auriga star forming region and is one of a handful of young systems to host a primordial circumbinary disk, as well as individual circumstellar disks. Using the the facility infrared, high-resolution NIRSPEC spectrograph behind the adaptive optics system at the 10-meter Keck II telescope, we observed a dramatic change in the spectra of UY Aur B between 2003 and 2010. We also identified flux variability in the individual components of 12 magnitudes, particularly in the secondary star, on the basis of historical photometry. Thermal dust and line emission observed with millimeter interferometry indicates complex dynamical behavior of the circumbinary and circumstellar dust and led Tang et al. (2014) to speculate that UY Aur B may itself be a binary. Our adaptive optics imaging with the Keck II telescope showed no evidence for a close companion to the B component, although the marked change in our spectra of this star suggest that it could be a spectroscopic binary. We are currently limited by the paucity of angularly resolved observations, both photometric and spectroscopic, hampering the interpretation of the data. High-cadence, angularly resolved spectroscopy and photometry will be required to confirm the potential higher-order multiplicity of this system. This research was supported in part by NSF grants AST-1461200 and AST-1313399.
  145. Plavchan, P., Gao, P., Gagne, J., et al., (including von Braun, K.), 2017, AAS, 229, 320.04, Discovery of Two Jovian Planet Candidates Around AU Mic
    We present a pair of candidate Jovian exoplanets discovered with the radial velocity (RV) technique in the near-infrared (NIR) orbiting the young M dwarf star AU Mic (a ~ 0.3 and 3.5 AU; M_p ~ 1.5 and 6 M_J). Data were obtained at 2.3 microns from 2010-2016 with the R=46,000 CSHELL spectrograph at the NASA Infrared Telescope Facility, and from 2005-2007 with the R=25,000 NIRSPEC spectrograph at the Keck Observatory. AU Mic possesses long-lived BY Draconis type polar starspots with a known rotation period of 4.865 days. No signal in the NIR RVs is identified that is consistent with the rotation period of the star, but stellar activity remains a possible explanation for the observed NIR RV variability. The outer Jovian planet candidate offers a plausible dynamical explanation for the observed debris disk dynamics of moving "clumps" on several year time-scales. It may be possible to directly image the outer planet candidate with the current generation of high contrast imaging instruments. If confirmed, this discovery would demonstrate the utility of RV precursor observations for informing direct imaging surveys and the utility of NIR RV searches for planets around young and/or active stars. These results also point to the promise of future NIR precise RVs, including iSHELL, SPIRou, HPF and CARMENES, which will operate at higher precision and with larger spectral grasp than CSHELL.
  146. Prato, L., 2017, AAS, 229, 338.04, The Lowell Observatory Predoctoral Scholar Program
    Lowell Observatory is pleased to solicit applications for our Predoctoral Scholar Fellowship Program. Now beginning its ninth 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. The Observatory's new 4.3 meter Discovery Channel Telescope is now operating at full science capacity. 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 2017 are due by May 1, 2017; alternate application dates will be considered on an individual basis.
  147. Paust, N., Wilson, D., van Belle, G., 2017, AAS, 229, 343.19, Star Cluster Mass Functions and Hierarchical Clustering: Learning from Koposov 1 and 2
    We present photometry of two halo star clusters, Koposov 1 and 2. Found as over-densities in the Sloan Digital Sky Survey, these clusters were intially believed to be heavily stripped globular clusters, given the small number of stars per cluster. In this work, we have used isochrone fitting to determine the age, distance, and metallicity of the clusters. These results confirm tha tthe clusters are in the halo but also reveal surprisingly young ages and high metallicities. Investigation of the cluster mass functions reveals a steep negatively-sloped present day mass function in contrast to the flatish positively-sloped mass functions seen in heavily stripped Galactic globular clusters. The mass function slope, proximity to the Sagittarius stream, and common metallicity with M54, which is related to the Sagittarius dwarf, leads to a very interesting conclusion: Koposov 1 and 2 are open clusters removed from the Sagittarius dwarf through tidal stripping.
  148. Cale, B., Plavchan, P., Nishimoto, A., et al., (including von Braun, K.), 2017, AAS, 229, 403.06, Precise Radial Velocity First Light Observations With iSHELL
    We present our first light observations with the new iSHELL spectrograph at the NASA Infrared Telescope facility. iShell replaces the 25 year old CSHELL with improvements in spectral grasp (~40x), resolution (70,000 versus 46,000), throughput, optics, and detector characteristics. With CSHELL, we obtained a radial velocity precision of 3 m/s on a bright red giant and we identified several radial velocity variable M dwarfs for future follow up. Our goal with iSHELL is to characterize the precise radial velocity performance of the methane isotopologue absorption gas cell in the calibration unit. We observe bright nearby radial velocity standards to better understand the instrument and data reduction techniques. We have updated our CSHELL analysis code to handle multiple orders and the increased number of pixels. It is feasible that we will obtain a radial velocity precision of < 3 m/s, sufficient to detect terrestrial planets in the habitable zone of nearby M dwarfs. We will also follow up radial velocity variables we have discovered, along with transiting exoplanets orbiting M dwarfs identified with the K2 and TESS missions.
  149. Gregg, M., West, M., 2017, AAS, 229, 427.07, Ram Pressure Stripping and Morphological Transformation in the Coma Cluster
    The two largest spiral galaxies in the Coma cluster, NGC4911 and NGC4921, exhibit signs of being vigorously ram-pressure stripped by the hot intracluster medium. HST ACS and WFC3 images have revealed galactic scale shock fronts, giant "Pillars of Creation", rivulets of dust, and spatially coherent star formation in these grand design spirals. All evidence points to these galaxies being stressed by a global external source which can only be the hot intracluster medium (ICM). Inspired by these examples, we have obtained HST WFC3 imaging of five additional large spirals to search for and investigate the effects of ram pressure stripping across the wider Coma cluster. The results are equally spectacular as the first two examples. The geometry of the interactions in some cases allows us to estimate the various time scales involved, including gas flows out of the disk leading to creation of the ICM, and the attendant triggered star formation in the galaxy disks. The global star formation patterns and wholesale tidal stripping of matter yield insights into the spatial and temporal ISM-ICM interactions driving the evolution of galaxies in clusters and ultimately transforming their morphologies from spiral to S0. These processes, much more common in the early Universe, led to the wholesale morphological transformation of Hubble types during the assembly of rich clusters, when the intergalactic populations and hot ICM were first being created and laid down from such stripping and destruction of their member galaxies.We also report on two instrumental aspects of WFC3: 1) using the filter pair F350LP and F600LP to create an extremely broad pseudo Blue-Red color to achieve the greatest observing efficiency with HST, and 2) a WFC3 CCD effect which leads to apparent quantization of background counts, making automatic sky determination challenging when using drizzlepac routines.
  150. Beck, M., Massey, P., 2017, AAS, 229, 433.04, The Red Supergiants of M33: Determining Physical Properties
    We investigate a sample of red supergiants in the nearby unbarred spiral galaxy M33 with the goals of (1) determining the physical properties of these stars, (2) understanding the effects of metallicity on massive star evolution, and (3) comparing results to current models proposed by the Geneva group. M33 provides an ideal environment in which to conduct this examination because of a gradient of metallicity within its disk as well as its proximity to the Milky Way, which allows us to observe a complete sample of red supergiants. We employ MARCS atmosphere models and fit spectral features of our stars to determine effective temperatures and spectral types, then we use this information in combination with photometry to calculate bolometric luminosities. After placing these objects on the H-R diagram, we notice some discrepancies with what the Geneva solar-metallicity evolutionary tracks (Ekstrom et al. 2012) predict, namely that the tracks may not extend to cool enough temperatures and high enough luminosities and masses to comply with what we see observationally. We propose this may be the result of a mismatch between M33s metallicity and the solar-metallicity Geneva models; we hope to make comparisons in the future as these new evolutionary tracks become available. This work was supported by the NSF through grant numbers AST-1461200 and AST-1612874.
  151. Massey, P., 2017, adap, 17-ADAP17-10, The Fundamental Physical Properties of Wolf-Rayet Stars
    Massive stars are the cosmic engines that power the far-infrared luminosities of distant galaxies, and dominate the ionization of nearby HII regions. They are the primary source of carbon and oxygen in the Universe, and their core collapses manufacture all of the elements heavier than Fe. The re-ionization of the early Universe was thanks to Population III massive stars, and the super-massive black holes we find in the cores of galaxies today were seeded as a result of the black holes that formed from the first generations of massive stars. Understanding massive star evolution is the key to unlocking many astrophysical problems. The largest uncertainty in massive star evolution is the question of how Wolf-Rayet (WR) stars form. Our proposal will determine the fundamental physical properties of WRs using four archival NASA data sets for a critical comparison with present day evolution models. It is generally assumed that massive stars spend most of their post-main-sequence lives WRs. For decades we have believed that WRs form as a result of stellar winds stripping off the H-rich outer layers of a star, leaving behind a bare stellar core. In this picture, WRs are a normal stage in the evolution of the most massive stars. Recently, this scenario has been called into question. Stellar wind mass- loss rates are now known to be significantly lower than previously thought, although whether this is a factor of 3 or 10 remains unclear. If the latter is correct, then this poses a serious problem for the formation of WRs. This has created a paradigm shift, with increased importance attached to the role of binary evolution, with Roche-lobe overflow performing the stripping. Attempts to distinguish which scenario is more prevalent is complicated by the possibility of past mergers; i.e., just because a WR is not a binary today does not prove it was not one in the past. We will tackle this question from a fresh perspective, determining reliable fundamental physical properties of WRs and seeing whether they better match the single or binary star evolutionary models. If they agree with the single-star models, that is compelling evidence that WRs are a normal part of the evolution of massive stars. If they disagree, perhaps either binary evolution plays an important role in the formation of WRs or the single star models could be improved. For instance, we know that the mass-loss rates during the Luminous Blue Variable and red supergiant phases are poorly constrained by observations. If higher mass loss rates during these phases were included, could we account for all of the WR physical properties (including chemical abundances) that we find? Either result will help us learn more about the origin of WRs while also testing and helping improve the evolutionary models. For this test to be meaningful, we must have accurate measurements of the fundamental physical properties of WRs (such as effective temperatures, bolometric luminosities, and chemical abundances), as well as having a good understanding of the uncertainties on these quantities. To achieve this, we have a selected a statistically large sample of 27 WRs in the Small and Large Magellanic Clouds which possess excellent UV spectra in the MAST IUE archive. This wavelength is crucial, as it contains key diagnostic resonance lines, such as CIV 1550. To these, we add our own high quality Magellan optical (and, when needed, near-IR) spectrophotometry. Forty percent of our sample has also been observed in the far-UV with FUSE, providing additional diagnostics. Finally, we will incorporate NASA 2MASS and Spitzer IPAC photometry, which extend the spectral energy distribution into the IR. We will model each of these combined data sets using CMFGEN, a stellar atmosphere code that includes the many complications needed to model the spectra of these stars. The use of this combined data set achieves what one could not hope to do from any one of them, consistent with the aims of the ADAP.
  152. Elmegreen, B., Hunter, D., 2017, ASSL, 434, 115, Outskirts of Nearby Disk Galaxies: Star Formation and Stellar Populations
    The properties and star formation processes in the far-outer disks of nearby spiral and dwarf irregular galaxies are reviewed. The origin and structure of the generally exponential profiles in stellar disks is considered to result from cosmological infall combined with a non-linear star formation law and a history of stellar migration and scattering from spirals, bars and random collisions with interstellar clouds. In both spirals and dwarfs, the far-outer disks tend to be older, redder and thicker than the inner disks, with the overall radial profiles suggesting inside-out star formation plus stellar scattering in spirals and outside-in star formation with a possible contribution from scattering in dwarfs. Dwarf irregulars and the far-outer parts of spirals both tend to be gas dominated, and the gas radial profile is often non-exponential although still decreasing with radius. The ratio of H to far-UV flux tends to decrease with lower surface brightness in these regions, suggesting either a change in the initial stellar mass function or the sampling of that function or a possible loss of H photons.

    153. 152 publications and 2524 citations in 2017.

152 publications and 2524 citations total.

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