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Research involving Lowell Observatory staff 2017
(Articles and chapters)

This is a work ever in progress.

(Pulled from ADS* by sel on 2023-05-29)

*We are grateful for all the effort that went into making The SAO/NASA Astrophysics Data System (ADS) possible. The ADS is operated by the Smithsonian Astrophysical Observatory under NASA Cooperative Agreement NNX16AC86A and can be found at: https://ui.adsabs.harvard.edu/

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Years: 2017 Bottom


  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., Lopez, E., Howard, A., Isaacson, H., Sinukoff, E., Vanderburg, A., Nofi, L., Yu, J., North, T., Chaplin, W., Foreman-Mackey, D., Petigura, E., Ansdell, M., Weiss, L., Fulton, B., Lin, D., 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., Parker, A., Beyer, R., Schenk, P., Howett, C., Stern, S., Reuter, D., Weaver, H., Young, L., Ennico, K., Binzel, R., Buie, M., Cook, J., Cruikshank, D., Ore, C., Earle, A., Jennings, D., Singer, K., Linscott, I., Lunsford, A., Protopapa, S., Schmitt, B., Weigle, E., the New Horizons Science Team, 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., Batalha, N., Henze, C., Ciardi, D., Barclay, T., Borucki, W., Buchhave, L., Crepp, J., Everett, M., Horch, E., Howard, A., Howell, S., Isaacson, H., Jenkins, J., Latham, D., Petigura, E., Quintana, 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. Raiteri, C., Villata, M., Acosta-Pulido, J., Agudo, I., Arkharov, A., Bachev, R., Baida, G., Benitez, E., Borman, G., Boschin, W., Bozhilov, V., Butuzova, M., Calcidese, P., Carnerero, M., Carosati, D., Casadio, C., Castro-Segura, N., Chen, W., Damljanovic, G., D'Ammando, F., di Paola, A., Echevarria, J., Efimova, N., Ehgamberdiev, S., Espinosa, C., Fuentes, A., Giunta, A., Gomez, J., Grishina, T., Gurwell, M., Hiriart, D., Jermak, H., Jordan, B., Jorstad, S., Joshi, M., Kopatskaya, E., Kuratov, K., Kurtanidze, O., Kurtanidze, S., Lahteenmaki, A., Larionov, V., Larionova, E., Larionova, L., Lazaro, C., Lin, C., Malmrose, M., Marscher, A., Matsumoto, K., McBreen, B., Michel, R., Mihov, B., Minev, M., Mirzaqulov, D., Mokrushina, A., Molina, S., Moody, J., Morozova, D., Nazarov, S., Nikolashvili, M., Ohlert, J., Okhmat, D., Ovcharov, E., Pinna, F., Polakis, T., Protasio, C., Pursimo, T., Redondo-Lorenzo, F., Rizzi, N., Rodriguez-Coira, G., Sadakane, K., Sadun, A., Samal, M., Savchenko, S., Semkov, E., Skiff, B., Slavcheva-Mihova, L., Smith, P., Steele, I., Strigachev, A., Tammi, J., Thum, C., Tornikoski, M., Troitskaya, Y., Troitsky, I., Vasilyev, A., Vince, O., 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.
  6. Angerhausen, D., Dreyer, C., Placek, B., Csizmadia, S., Eigmuller, P., Godolt, M., Kitzmann, D., Mallonn, M., Becklin, E., Collins, P., Dunham, E., Grenfell, J., Hamilton, R., Kabath, P., Logsdon, S., Mandell, A., Mandushev, G., McElwain, M., McLean, I., Pfueller, E., Rauer, H., Savage, M., Shenoy, S., Vacca, W., Van Cleve, J., Wiedemann, M., Wolf, J., 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 ( or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/608/A120

  7. 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.
  8. Polishook, D., Moskovitz, N., Thirouin, A., Bosh, A., Levine, S., Zuluaga, C., Tegler, S., Aharonson, O., 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.
  9. Pasachoff, J., Babcock, B., Durst, R., Seeger, C., Levine, S., Bosh, A., Person, M., Sickafoose, A., Zuluaga, C., Kosiarek, M., Abe, F., Nagakane, M., Suzuki, D., Tristram, P., Arredondo, 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.
  10. Massey, P., Levesque, E., Neugent, K., Evans, K., Drout, M., Beck, M., 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.
  11. Neugent, K., Massey, P., Hillier, D., Morrell, N., 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.
  12. Leith, T., Moskovitz, N., Mayne, R., DeMeo, F., Takir, D., Burt, B., Binzel, R., Pefkou, D., 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.
  13. De Marco, O., Reichardt, T., Iaconi, R., Hillwig, T., Jacoby, G., Keller, D., Izzard, R., Nordhaus, J., Blackman, E., 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.
  14. Nicholl, M., Berger, E., Kasen, D., Metzger, B., Elias, J., Briceno, C., Alexander, K., Blanchard, P., Chornock, R., Cowperthwaite, P., Eftekhari, T., Fong, W., Margutti, R., Villar, V., Williams, P., Brown, W., Annis, J., Bahramian, A., Brout, D., Brown, D., Chen, H., Clemens, J., Dennihy, E., Dunlap, B., Holz, D., Marchesini, E., Massaro, F., Moskowitz, N., Pelisoli, I., Rest, A., Ricci, F., Sako, M., Soares-Santos, M., Strader, J., 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.
  15. Dahn, C., Harris, H., Subasavage, J., Ables, H., Canzian, B., Guetter, H., Harris, F., Henden, A., Leggett, S., Levine, S., Luginbuhl, C., Monet, A., Monet, D., Munn, J., Pier, J., Stone, R., Vrba, F., Walker, R., Tilleman, T., 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.
  16. Egeland, R., Soon, W., Baliunas, S., Hall, J., Henry, G., 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.
  17. 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.
  18. Fares, R., Bourrier, V., Vidotto, A., Moutou, C., Jardine, M., Zarka, P., Helling, C., Lecavelier des Etangs, A., Llama, J., Louden, T., Wheatley, P., Ehrenreich, D., 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.
  19. Howard, A., Moore, J., White, O., Umurhan, O., Schenk, P., Grundy, W., Schmitt, B., Philippe, S., McKinnon, W., Spencer, J., Beyer, R., Stern, S., Ennico, K., Olkin, C., Weaver, H., Young, L., New Horizons Science Team, 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.
  20. 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'.

  21. Henden, A., Levine, S., Welch, D., Terrell, D., Munari, U., Smith, T., 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.
  22. Allen, T., Prato, L., Wright-Garba, N., Schaefer, G., Biddle, L., Skiff, B., Avilez, I., Muzzio, R., Simon, M., 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.
  23. Boyajian, T., von Braun, K., van Belle, G., McAlister, H., ten Brummelaar, T., Kane, S., Muirhead, P., Jones, J., White, R., Schaefer, G., Ciardi, D., Henry, T., Lopez-Morales, M., Ridgway, S., Gies, D., Jao, W., Rojas-Ayala, B., Parks, J., Sturmann, L., Sturmann, J., Turner, N., Farrington, C., Goldfinger, P., Berger, D., 2017, ApJ, 845, 178, Erratum: Stellar Diameters and Temperatures. II. Main-sequence K- and M-stars (2012, ApJ, 757, 112)
  24. Santos-Sanz, P., Lellouch, E., Groussin, O., Lacerda, P., Muller, T., Ortiz, J., Kiss, C., Vilenius, E., Stansberry, J., Duffard, R., Fornasier, S., Jorda, L., 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.

  25. 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.
  26. Simon, M., Guilloteau, S., Di Folco, E., Dutrey, A., Grosso, N., Pietu, V., Chapillon, E., Prato, L., Schaefer, G., Rice, E., Boehler, Y., 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.
  27. Kellogg, K., Prato, L., Torres, G., Schaefer, G., Avilez, I., Ruiz-Rodriguez, D., Wasserman, L., Bonanos, A., Guenther, E., Neuhauser, R., Levine, S., Bosh, A., Morzinski, K., Close, L., Bailey, V., Hinz, P., Males, J., 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.
  28. 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.
  29. Knight, M., Snodgrass, C., Vincent, J., Conn, B., Skiff, B., Schleicher, D., Lister, T., 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.
  30. 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.
  31. 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.
  32. 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.
  33. Zellem, R., Swain, M., Roudier, G., Shkolnik, E., Creech-Eakman, M., Ciardi, D., Line, M., Iyer, A., Bryden, G., Llama, J., Fahy, K., 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.
  34. Zavala, R., Hummel, C., Boboltz, D., Ojha, R., Shaffer, D., Tycner, C., Richards, M., Hutter, D., 2017, ApJL, 843, L18, Erratum: The Algol Triple System Spatially Resolved at Optical Wavelengths (2010, ApJL, 715, L44)
  35. West, M., de Propris, R., Bremer, M., Phillipps, S., 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.
  36. Dias-Oliveira, A., Sicardy, B., Ortiz, J., Braga-Ribas, F., Leiva, R., Vieira-Martins, R., Benedetti-Rossi, G., Camargo, J., Assafin, M., Gomes-Junior, A., Baug, T., Chandrasekhar, T., Desmars, J., Duffard, R., Santos-Sanz, P., Ergang, Z., Ganesh, S., Ikari, Y., Irawati, P., Jain, J., Liying, Z., Richichi, A., Shengbang, Q., Behrend, R., Benkhaldoun, Z., Brosch, N., Daassou, A., Frappa, E., Gal-Yam, A., Garcia-Lozano, R., Gillon, M., Jehin, E., Kaspi, S., Klotz, A., Lecacheux, J., Mahasena, P., Manfroid, J., Manulis, I., Maury, A., Mohan, V., Morales, N., Ofek, E., Rinner, C., Sharma, A., Sposetti, S., Tanga, P., Thirouin, A., Vachier, F., Widemann, T., Asai, A., Hayato, W., Hiroyuki, W., Owada, M., Yamamura, H., Hayamizu, T., Bradshaw, J., Kerr, S., Tomioka, H., Andersson, S., Dangl, G., Haymes, T., Naves, R., Wortmann, G., 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).
  37. 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.

  38. Adamo, A., Ryon, J., Messa, M., Kim, H., Grasha, K., Cook, D., Calzetti, D., Lee, J., Whitmore, B., Elmegreen, B., Ubeda, L., Smith, L., Bright, S., Runnholm, A., Andrews, J., Fumagalli, M., Gouliermis, D., Kahre, L., Nair, P., Thilker, D., Walterbos, R., Wofford, A., Aloisi, A., Ashworth, G., Brown, T., Chandar, R., Christian, C., Cignoni, M., Clayton, G., Dale, D., de Mink, S., Dobbs, C., Elmegreen, D., Evans, A., Gallagher, J., Grebel, E., Herrero, A., Hunter, D., Johnson, K., Kennicutt, R., Krumholz, M., Lennon, D., Levay, K., Martin, C., Nota, A., Ostlin, G., Pellerin, A., Prieto, J., Regan, M., Sabbi, E., Sacchi, E., Schaerer, D., Schiminovich, D., Shabani, F., Tosi, M., Van Dyk, S., Zackrisson, E., 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.

  39. McKinnon, W., Stern, S., Weaver, H., Nimmo, F., Bierson, C., Grundy, W., Cook, J., Cruikshank, D., Parker, A., Moore, J., Spencer, J., Young, L., Olkin, C., Ennico Smith, K., New Horizons Geology, G., Imaging, Composition Theme Teams, 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.
  40. Binzel, R., Earle, A., Buie, M., Young, L., Stern, S., Olkin, C., Ennico, K., Moore, J., Grundy, W., Weaver, H., Lisse, C., Lauer, T., New Horizons Geology, Geophysics Imaging Team, 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.
  41. Earle, A., Binzel, R., Young, L., Stern, S., Ennico, K., Grundy, W., Olkin, C., Weaver, H., New Horizons Geology and Geophysics Imaging Team, 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.
  42. Howett, C., Parker, A., Olkin, C., Reuter, D., Ennico, K., Grundy, W., Graps, A., Harrison, K., Throop, H., Buie, M., Lovering, J., Porter, S., Weaver, H., Young, L., Stern, S., Beyer, R., Binzel, R., Buratti, B., Cheng, A., Cook, J., Cruikshank, D., Dalle Ore, C., Earle, A., Jennings, D., Linscott, I., Lunsford, A., Parker, J., Phillippe, S., Protopapa, S., Quirico, E., Schenk, P., Schmitt, B., Singer, K., Spencer, J., Stansberry, J., Tsang, C., Weigle, G., Verbiscer, A., 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.
  43. Howett, C., Ennico, K., Olkin, C., Buie, M., Verbiscer, A., Zangari, A., Parker, A., Reuter, D., Grundy, W., Weaver, H., Young, L., Stern, S., 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.
  44. Robbins, S., Singer, K., Bray, V., Schenk, P., Lauer, T., Weaver, H., Runyon, K., McKinnon, W., Beyer, R., Porter, S., White, O., Hofgartner, J., Zangari, A., Moore, J., Young, L., Spencer, J., Binzel, R., Buie, M., Buratti, B., Cheng, A., Grundy, W., Linscott, I., Reitsema, H., Reuter, D., Showalter, M., Tyler, G., Olkin, C., Ennico, K., Stern, S., New Horizons Lorri, M., 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.
  45. Buratti, B., Hofgartner, J., Hicks, M., Weaver, H., Stern, S., Momary, T., Mosher, J., Beyer, R., Verbiscer, A., Zangari, A., Young, L., Lisse, C., Singer, K., Cheng, A., Grundy, W., Ennico, K., Olkin, C., 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.
  46. Protopapa, S., Grundy, W., Reuter, D., Hamilton, D., Dalle Ore, C., Cook, J., Cruikshank, D., Schmitt, B., Philippe, S., Quirico, E., Binzel, R., Earle, A., Ennico, K., Howett, C., Lunsford, A., Olkin, C., Parker, A., Singer, K., Stern, A., Verbiscer, A., Weaver, H., Young, L., New Horizons Science Team, 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.
  47. Schmitt, B., Philippe, S., Grundy, W., Reuter, D., Cote, R., Quirico, E., Protopapa, S., Young, L., Binzel, R., Cook, J., Cruikshank, D., Dalle Ore, C., Earle, A., Ennico, K., Howett, C., Jennings, D., Linscott, I., Lunsford, A., Olkin, C., Parker, A., Parker, J., Singer, K., Spencer, J., Stansberry, J., Stern, S., Tsang, C., Verbiscer, A., Weaver, H., New Horizons Science Team, 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.

  48. White, O., Moore, J., McKinnon, W., Spencer, J., Howard, A., Schenk, P., Beyer, R., Nimmo, F., Singer, K., Umurhan, O., Stern, S., Ennico, K., Olkin, C., Weaver, H., Young, L., Cheng, A., Bertrand, T., Binzel, R., Earle, A., Grundy, W., Lauer, T., Protopapa, S., Robbins, S., Schmitt, B., New Horizons Science Team, 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.
  49. Moore, J., Howard, A., Umurhan, O., White, O., Schenk, P., Beyer, R., McKinnon, W., Spencer, J., Grundy, W., Lauer, T., Nimmo, F., Young, L., Stern, S., Weaver, H., Olkin, C., Ennico, K., New Horizons Science Team, 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.
  50. Snodgrass, C., A'Hearn, M., Aceituno, F., Afanasiev, V., Bagnulo, S., Bauer, J., Bergond, G., Besse, S., Biver, N., Bodewits, D., Boehnhardt, H., Bonev, B., Borisov, G., Carry, B., Casanova, V., Cochran, A., Conn, B., Davidsson, B., Davies, J., de Leon, J., de Mooij, E., de Val-Borro, M., Delacruz, M., DiSanti, M., Drew, J., Duffard, R., Edberg, N., Faggi, S., Feaga, L., Fitzsimmons, A., Fujiwara, H., Gibb, E., Gillon, M., Green, S., Guijarro, A., Guilbert-Lepoutre, A., Gutierrez, P., Hadamcik, E., Hainaut, O., Haque, S., Hedrosa, R., Hines, D., Hopp, U., Hoyo, F., Hutsemekers, D., Hyland, M., Ivanova, O., Jehin, E., Jones, G., Keane, J., Kelley, M., Kiselev, N., Kleyna, J., Kluge, M., Knight, M., Kokotanekova, R., Koschny, D., Kramer, E., Lopez-Moreno, J., Lacerda, P., Lara, L., Lasue, J., Lehto, H., Levasseur-Regourd, A., Licandro, J., Lin, Z., Lister, T., Lowry, S., Mainzer, A., Manfroid, J., Marchant, J., McKay, A., McNeill, A., Meech, K., Micheli, M., Mohammed, I., Monguio, M., Moreno, F., Munoz, O., Mumma, M., Nikolov, P., Opitom, C., Ortiz, J., Paganini, L., Pajuelo, M., Pozuelos, F., Protopapa, S., Pursimo, T., Rajkumar, B., Ramanjooloo, Y., Ramos, E., Ries, C., Riffeser, A., Rosenbush, V., Rousselot, P., Ryan, E., Santos-Sanz, P., Schleicher, D., Schmidt, M., Schulz, R., Sen, A., Somero, A., Sota, A., Stinson, A., Sunshine, J., Thompson, A., Tozzi, G., Tubiana, C., Villanueva, G., Wang, X., Wooden, D., Yagi, M., Yang, B., Zaprudin, B., Zegmott, T., 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'.

  51. Neugent, K., Massey, P., Hillier, D., Morrell, N., 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.

  52. Daemgen, S., Todorov, K., Silva, J., Hand, D., Garcia, E., Currie, T., Burrows, A., Stassun, K., Ratzka, T., Debes, J., Lafreniere, D., Jayawardhana, R., Correia, S., 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.
  53. 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.
  54. 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.
  55. Pilyavsky, G., Mauskopf, P., Smith, N., Schroeder, E., Sinclair, A., van Belle, G., Hinkel, N., Scowen, P., 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.
  56. Maier, E., Elmegreen, B., Hunter, D., Chien, L., Hollyday, G., Simpson, C., 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.
  57. Furlan, E., Ciardi, D., Everett, M., Saylors, M., Teske, J., Horch, E., Howell, S., van Belle, G., Hirsch, L., Gautier, T., Adams, E., Barrado, D., Cartier, K., Dressing, C., Dupree, A., Gilliland, R., Lillo-Box, J., Lucas, P., Wang, J., 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)
  58. Hunter, D., 2017, PASP, 129, 040201, Vera Cooper Rubin (1928-2016)
  59. Moskovitz, N., Polishook, D., DeMeo, F., Binzel, R., Endicott, T., Yang, B., Howell, E., Vervack, R., Fernandez, Y., 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.
  60. Holler, B., Young, L., Buie, M., Grundy, W., Lyke, J., Young, E., 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.
  61. Martin, E., Mace, G., McLean, I., Logsdon, S., Rice, E., Kirkpatrick, J., Burgasser, A., McGovern, M., 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.

  62. 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.
  63. Rubio, M., Elmegreen, B., Hunter, D., Cortes, J., Brinks, E., Cigan, P., 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..
  64. Hillwig, T., Jacoby, G., Jones, D., De Marco, O., 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.
  65. Oszkiewicz, D., Skiff, B., Moskovitz, N., Kankiewicz, P., Marciniak, A., Licandro, J., Galiazzo, M., Zeilinger, W., 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.
  66. 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.

  67. Furlan, E., Ciardi, D., Everett, M., Saylors, M., Teske, J., Horch, E., Howell, S., van Belle, G., Hirsch, L., Gautier, T., Adams, E., Barrado, D., Cartier, K., Dressing, C., Dupree, A., Gilliland, R., Lillo-Box, J., Lucas, P., Wang, J., 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.
  68. Jacoby, G., De Marco, O., Davies, J., Lotarevich, I., Bond, H., Harrington, J., Lanz, T., 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.

  69. Johnson, M., Hunter, D., Kamphuis, P., Wang, J., 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.
  70. Vokrouhlicky, D., Pravec, P., Durech, J., Bolin, B., Jedicke, R., Kusnirak, P., Galad, A., Hornoch, K., Kryszczynska, A., Colas, F., Moskovitz, N., Thirouin, A., Nesvorny, D., 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.
  71. Kane, S., von Braun, K., Henry, G., Waters, M., Boyajian, T., Mann, A., 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.
  72. 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.
  73. Garcia, E., Currie, T., Guyon, O., Stassun, K., Jovanovic, N., Lozi, J., Kudo, T., Doughty, D., Schlieder, J., Kwon, J., Uyama, T., Kuzuhara, M., Carson, J., Nakagawa, T., Hashimoto, J., Kusakabe, N., Abe, L., Brandner, W., Brandt, T., Feldt, M., Goto, M., Grady, C., Hayano, Y., Hayashi, M., Hayashi, S., Henning, T., Hodapp, K., Ishii, M., Iye, M., Janson, M., Kandori, R., Knapp, G., Matsuo, T., McElwain, M., Miyama, S., Morino, J., Moro-Martin, A., Nishimura, T., Pyo, T., Serabyn, E., Suenaga, T., Suto, H., Suzuki, R., Takahashi, Y., Takami, H., Takami, M., Takato, N., Terada, H., Thalmann, C., Turner, E., Watanabe, M., Wisniewski, J., Yamada, T., Usuda, T., Tamura, M., 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.
  74. Egeland, R., Soon, W., Baliunas, S., Hall, J., Pevtsov, A., Bertello, L., 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.
  75. Swihart, S., Garcia, E., Stassun, K., van Belle, G., Mutterspaugh, M., Elias, N., 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.
  76. Hunter, D., Ficut-Vicas, D., Ashley, T., Brinks, E., Cigan, P., Elmegreen, B., Heesen, V., Herrmann, K., Johnson, M., Oh, S., Rupen, M., Schruba, A., Simpson, C., Walter, F., Westpfahl, D., Young, L., Zhang, H., 2017, AJ, 153, 47, Erratum: "Little Things" (2012, AJ, 144, 134)
  77. 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)
  78. 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.
  79. 78 publications and 2215 citations in 2017.

78 publications and 2215 citations total.