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Research involving Lowell Observatory staff 2019
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  1. Steckloff, J., Soto, A., Soderblom, J., et al., (including Hanley, J., Grundy, W.), 2019, AGUFM, 2019, P21C-02, Titan's Bistable Climate and the Origin of its Atmospheric Methane
    Saturn's largest moon, Titan, hosts a methane-driven hydrological cycle [1-2]. This methane has been in the atmosphere for less than 470 Myr [3]. However, the reservoir that released this methane is poorly understood. Here we show that Titan presently has a bistable climate, and that the atmospheric methane is released during a transition between climatic regimes: from the colder "Slushball Titan" regime (in which all surface methane is sequestered in the depths of a nearly global nitrogen-dominated ocean) to the present warm climatic regime in which nearly all surface methane is atmospheric.

    In the Slushball Titan regime, the lack of atmospheric methane results in frigid surface temperatures, well below 84 K [4-5], the tipping point between regimes. Under these conditions, Titan's atmosphere partially collapses into a nearly global ~70 m deep nitrogen ocean. Thermodynamics drive nearly all surface methane (whether atmospheric or geologically released) into this ocean.

    We propose that Titan was in a slushball climate until a few hundred Myr ago, until an energetic event (such as a large impact and/or changes in insolation) warmed Titan sufficiently to trigger a transition to the warm Titan climate. This transition would evaporate the nitrogen ocean and release its oceanic methane to the atmosphere. This atmospheric methane would further warm the moon and begin to experience photochemical processing. This scenario is consistent with Titan's surface cratering age (200-1000 Myr; [6]), the ~50-630 Myr required to form Titan's dune materials from atmospheric methane [7], and the ~300-1200 Myr required to explain Titan's global shape via ethane substitution in methane clathrates [8]. This is also consistent with the presence of fluvial features in Titan's low latitudes [9], the lower crater abundance at lower elevations [10], and the overabundance of small craters, which indicate that Titan's atmosphere was thinner in the past [6].

    [1] Tomasko et al. 2005. Nature 44, 61

    [2] Tokano et al. 2006. Nature 442, 432

    [3] Mandt et al. 2012. ApJ 749, 160

    [4] Lorenz, 1997. Science 275, 642

    [5] Charnay et al. 2014. Icarus 241, 269

    [6] Neish & Lorenz. 2012. P&SS 60, 26

    [7] Sotin et al. 2012. Icarus 221, 768

    [8] Chokrun & Sotin, 2012. GRL 39, L04201

    [9] Larsson & McKay. 2013. P&SS 78, 22

    [10] Neish & Lorenz. 2014. Icarus 228, 27

  2. Cartwright, R., Emery, J., Pinilla-Alonso, N., et al., (including Grundy, W.), 2019, AGUFM, 2019, P32A-08, Probing the regoliths of the classical Uranian satellites using near-infrared telescope observations: CO2 ice deposits mantled by a veneer of tiny H2O ice grains?
    In the late 1970s and early 1980s, near-infrared (NIR) ground-based observations (~1 - 2.5 m) determined that the surfaces of the large and tidally-locked "classical" moons of Uranus are composed of H2O ice, mixed with a dark, C-rich constituent. In the late 1990s and early 2000s, CO2 ice was detected in NIR spectra of these moons, with spectral properties remarkably similar to the second and third order combination and overtone bands of CO2 ice (between 1.9 to 2.1 m and 1.57 to 1.61 m, respectively). The presence of these relatively weak CO2 bands indicates that the detected CO2 ice is retained in thick deposits (~1 - 100 mm) on the surfaces of these moons. However, over longer NIR wavelengths (~3 - 5 m), the spectral signature of CO2 ice is mostly absent from these moons. Photon penetration depths into H2O-rich particulate surfaces are a steep function of wavelength, with NIR photons between 1 and 2.5 m penetrating deeper (~0.15 - 10 mm depths) than NIR photons between 3 and 5 m (~0.001 - 0.05 mm depths). Thus, we hypothesize that the regoliths of the classical Uranian satellites are compositionally stratified, with thick deposits of CO2 ice retained beneath a veneer of tiny H2O ice grains.

    To test this hypothesis, we have collected data using the Infrared Array Camera (IRAC) onboard the Spitzer Space Telescope (spanning ~3 to 5 m). We compared these new IRAC data to an IRAC dataset collected previously, as well as longer NIR spectra, spanning 3 to 4 m. Analysis of these longer NIR datasets indicates that the Uranian moons are relatively bright over the 3 to 5 m range, with enhanced 3.6-m H2O ice peaks. Best fit spectral models of the IRAC datasets are primarily composed of tiny H2O ice grains ( 2 m diameters), with no trace of CO2 ice. Thus, our analyses support compositional stratification of these moons' regoliths. We explore some of the processes that could generate layered media on the Uranian moons and discuss why the surfaces of icy Jovian and Saturnian moons lack similar veneers of tiny H2O ice grains. Additionally, we discuss how next generation telescopes and future spacecraft missions would revolutionize our understanding of the classical Uranian moons and ice giant planetary systems.

  3. Weaver, H., Porter, S., Spencer, J., et al., (including Grundy, W.), 2019, AGUFM, 2019, P33I-3531, Update on High Resolution Searches for KBO Binaries using New Horizons LORRI
    The New Horizons (NH) spacecraft has been traversing the Kuiper belt for the past four years, enabling observations of known Kuiper belt objects (KBOs) at unique geometries, including at large phase angles not possible from the inner solar system and at ranges that provide higher spatial resolution than available from Earth, or Earth-orbiting, facilities. New Horizons carries a large aperture (20.8 cm) visible light imaging system, the LOng Range Reconnaissance Imager (LORRI), whose resolution (IFOV=1,4 arcsec for 1x1 and 4x4 modes, respectively) permits searches for binaries at finer spatial scales than available from the Hubble Space Telescope (HST). We have already observed 13 KBOs (1 Plutino, 1 Hot Classical, 1 Scattered Disk, and 10 Cold Classicals) that passed within 1 AU of the NH spacecraft, and two more KBOs are scheduled for observations in early September 2019. We are actively searching for additional candidates using ground-based telescopes. Five of the observed KBOs passed within 0.2 AU of the NH spacecraft, including two with ranges of ~0.11 AU (82 km/pix for 1x1 mode). LORRI's photometric sensitivity for these satellite searches (V~16.3 in 1x1 mode after co-adding ~125 0.5s exposures; V~21 in 4x4 mode after co-adding ~50 30s exposures, and even deeper after implementing 64s exposures in fall 2019) is comparable to, or exceeds, that available from HST. Five of the six highest resolution (1x1 mode) NH KBO satellite searches were performed during the latter half of 2018, and some of those data are scheduled for downlink in Oct-Nov 2019. Here we report on the binary search limits achieved for the 1x1 data that were downlinked by the end of Nov 2019.
  4. Showalter, M., Benecchi, S., Buie, M., et al., (including Grundy, W.), 2019, AGUFM, 2019, P33I-3532, A Statistical Test for the Population of Contact Binaries in the Kuiper Belt
    New Horizons images of Kuiper Belt object (486958) 2014 MU69 dramatically revealed that it is a contact binary, comprising two flattened lobes attached by a very narrow neck. In spite of its highly elongated shape, MU69 has a rotational light curve with an amplitude that was too small to be measured from Earth or during the approach of the spacecraft in December 2018. This surprising result is, in part, a consequence of MU69's bilobate shape; in general, contact binaries have light curve amplitudes that are systematically lower than those of equivalent-area ellipsoids.

    The prevalence of contact binaries among the cold classical KBOs (CCKBOs) has been a topic of investigation on several fronts. We find that an important constraint on the answer to this question can be inferred from the statistical distribution of light curve amplitudes among CCKBOs. We have modeled these distributions based on a variety of assumptions, including rough or irregular shapes, albedo variations, degree of flattening, the size of the neck, and the size ratio of the two lobes. We have also explored the dependence on the statistical distribution of KBO orientations, assuming that the rotation poles are either completely random or are preferentially oriented normal to the orbit plane. In all cases, the distribution of light curve amplitudes is predicted to be lower if contact binaries are prevalent among the CCKBOs.

    At this time, the limited available data on CCKBO light curve amplitudes does not permit a definitive answer to the question of how many CCKBOs are contact binaries. However, the statistical test holds promise as more CCKBOs are observed. It would complement the shape determinations based on the direct modeling of KBOs with high-amplitude light curves, combined with further occultation studies of KBO shapes. Needed is a large and an unbiased sample of light curve amplitudes, one which does not focus on the high-amplitude light curves that are often of greatest interest.

  5. Singer, K., Spencer, J., McKinnon, W., et al., (including Grundy, W.), 2019, AGUFM, 2019, P33I-3535, Impact craters on 2014 MU69: Implications for Kuiper belt object size-frequency distributions and planetesimal formation
    Impact craters in the Pluto system as observed by New Horizons in July of 2015 revealed a previously-unknown deficit of small Kuiper belt objects (KBOs) less than ~1-2 km in diameter (Singer et al., 2019, Science) . New Horizons was poised to test this observation 3.5 years later with its next KBO close flyby of the cold classical KBO (486958) 2014 MU69 (nicknamed Ultima Thule). The images returned by New Horizons in early 2019 show MU69 is only modestly cratered, and potential craters on the surface show a shallow size-frequency distribution (SFD) similar to that of craters on Pluto and Charon (Stern et al. 2019, Science; Singer et al., 2019, EPSC-DPS; Spencer et al. 2019, Science).

    Some features on MU69 do have multiple morphologic indicators suggesting they are impact craters. There are regions on MU69 with few-to-no craters, even where the lighting is favorable for recognizing topographic features. The ~7-km-diameter depression (informally called Maryland) on the small lobe of MU69 is the largest easily observed feature that is likely to be an impact crater. There are also craters under 1 km in diameter, but no obvious craters between 1 and 7 km in diameter.

    The possible impact craters < ~1 km in diameter were divided into subgroups based on morphology, likelihood of being a crater , lighting geometry, and also into one possible geologic unit. Measurements/ratings were provided by several team members. All subgroups produced shallow-sloped SFDs (differential power-law slope -2) similar to those seen on Pluto and Charon for the same size craters (when scaled for gravity and impact velocity). Whole-sale resurfacing through geologic processes is not expected for MU69. Thus many more craters and at least some heavily cratered terrains would be predicted if the impactor SFD slope were steeper (an average differential slope closer to -3; Greenstreet et al. 2019, ApJ). Both the apparent lack of craters overall, and the shallow SFD slopes, are consistent with a relatively benign collisional environment for MU69 (McKinnon et al., 2019, Science).

  6. Lisse, C., Young, L., Cruikshank, D., et al., (including Grundy, W.), 2019, AGUFM, 2019, P33I-3540, On the Stability & Origin of MU69's and Pluto's Ices
    In this paper we discuss in a model-independent way the nature of the stable, refractory ices that could be present in Kuiper Belt object (KBO) 2014 MU69 ("Ultima Thule") after its 4.6 Gyr residence in the Edgeworth-Kuiper belt (EKB) as a cold classical object, and the processes that could affect them, such as short-lived radioactive decay, x-ray/ultraviolet photon (XUV) and galactic cosmic ray (GCR) irradiation, and micrometeorite bombardment. We compare the upper bounds for the gas production rate (~1024molecules/sec) measured by the New Horizons spacecraft flyby on 01 Jan 2019 to estimates for the outgassing flux rates from a suite of common cometary and KBO ices at the average ~40K sunlit surface temperature of UT, but do not find the upper limit very constraining except for the most volatile of species (eg CO, N2, CH4). More constraining is the stability versus sublimation into vacuum requirement over Myr to Gyr, and from this we find only 3 common ices that are truly refractory: HCN, CH3OH, and H2O (in order of increasing stability), while NH3and H2CO ices are marginally stable and may be removed by any positive temperature excursions in the EKB, as produced every 108- 109yrs by nearby supernovae (SN) and passing O/B stars. To date the New Horizons (NH) team has reported the presence of abundant CH3OH and H2O on MU69's surface (Stern+ 2019, Grundy+ 2019). NH3has been searched for, but not found. We predict that future absorption feature detections, if any are ever derived from higher SNR spectra, will be due to an HCN or poly-H2CO based species.

    Consideration of the conditions present in the EKB region during the formation era of MU69 lead us to state that it is highly likely that it "formed in the dark", unable to see the nascent, variable, highly luminous YSO/TTauri Sun, in an optically thick proto-planetary disk (PPD) mid-plane. Also, that KBOs contain pure CH3OH (and likely HCN) ice phases in addition to the H2O ice and H2O ice clathrates found in their short period (SP) comet descendants. Finally, when we apply our ice thermal stability analysis to bodies/populations related to MU69, we find that that Pluto must have gained its hypervolatiles from PPD sources in the first few Myr of the solar system's existence, that comet C/2016 R2 was placed onto an Oort Cloud orbit on a similar timescale, and that the O2in comet 67P is not primordial.

  7. Linscott, I., Asmar, S., Bird, M., et al., (including Grundy, W.), 2019, AGUFM, 2019, P34A-01, Pluto's Surface Properties from the New Horizons Uplink Bistatic Radar Experiment
    Exploration of planetary surface properties by scattering radio signals has been carried out via Solar System spacecraft for nearly six decades. During the New Horizons flyby of Pluto on July 14, 2015, an innovative approach reversed the radio path using a high-power uplink transmitted from the Deep Space Network. The uplink illuminated the surface of Pluto, and the scattered signals were recorded onboard the spacecraft by REX the Radioscience instrument, setting a record at 7.6 Bkm for bistatic radar. The high SNR advantage, needed to characterize such a distant object, was nearly three orders of magnitude greater than traditional downlink experiments could have provided.

    The bistatic experiment was performed using a radar transmission at 7.18 GHz, from the NASA's Deep Space Network 34-m diameter antenna (designated DSS-26) at Goldstone, California. The transmission was CW at 80 kilowatts in right-hand circular polarization (RCP) and was adjusted in frequency to compensate for predicted Doppler shifts to ensure it would fall within REX's 1.25 kHz bandpass. The received signal's SNR was 30x, (15 dB), and digitized by REX in both polarizations, and in-phase and quadrature, revealing a polarization ratio of ~1/2, and a surface reflectivity of ~0.3. The radar illumination at Pluto's specular point subtended an angle of incidence between 40 degrees and 60 degrees, a near-optimal geometry for modelling surface properties. Characterization of Pluto's surface in the vicinity of the specular point has incorporated Fresnel reflection, as well as electromagnetic scattering models for randomly oriented surface facets as well as subsurface propagation and multidimensional optimization over the distribution of surface slopes and roughness, to obtain both the composition and structure of Pluto's surface and subsurface.

    These results demonstrate the efficacy of bistatic scattering for planetary surface characterization and suggest that bistatic experiments, if incorporated in future missions to the solar system's planets, moons, dwarf planets and bodies, will substantially increase and enrich their science return.

  8. White, O., Moore, J., McKinnon, W., et al., (including Grundy, W.), 2019, AGUFM, 2019, P42C-01, The Geology and Formation of the Kuiper Belt Object 2014 MU69
    The New Horizons flyby of the small Kuiper Belt Object 2014 MU69 provided the first look at the geology of a member of the Cold Classical Kuiper Belt, the most primitive known population of objects in the solar system. MU69 is a contact binary, composed of two sharply distinct components (nicknamed "Ultima" and "Thule") that make contact at a bright, narrow, "neck". Both are flattened, with their smallest axes aligned, and their contact point is close to the longest axis of both bodies. This configuration strongly suggests that the two components formed independently, and orbited each other in a tidally locked configuration before coming gently together. The current rotation period of 15.92 hours is slow enough that, for reasonable densities, the two bodies must have lost significant angular momentum after contacting each other. On both components, the surface is generally smooth, though pits are seen near the terminator, and bright spots away from the terminator may also be bright-floored pits. If impact-generated, these features indicate a surface age dating to the era of planetary accretion.

    Ultima, the larger component, is highly flattened, with approximate dimensions 20.6 19.9 9.4 km. Thule is closer to spherical than Ultima, with approximate dimensions 15.4 13.8 9.8 km. In both cases, the shortest dimension is the least certain. Ultima appears to be divided into several sub-units, distinguished by surface texture and/or separated by linear scarps or bright linear albedo features. Dark features that appear to be low hills and ridges are unevenly distributed across the surface. The sub-units may provide evidence for assembly of Ultima from smaller bodies, though the continuity of some surface texture units across some of the bounding linear features argues for some of the unit boundaries being relatively young rather than primordial.

    Thule is markedly different in appearance. It is dominated by a large depression (nicknamed "Maryland") that is 7 km across and 0.5-1 km deep, and which is likely to be an impact feature. The rest of the surface is characterized by bright and dark albedo markings that often have strikingly sinuous boundaries, possibly due to sublimation erosion of thin, discrete surface layers.

    This work was supported by the NASA New Horizons project.

  9. Protopapa, S., Grundy, W., Cruikshank, D., et al., 2019, AGUFM, 2019, P42C-04, Surface compositions and colors of Pluto, its system of moons, and 2014 MU69
    The trans-neptunian population is extremely diverse, with bodies ranging from geologically-active, atmosphere-bearing, volatile-dominated dwarf planets to small primitive planetesimals lacking abundant surface volatile ices (e.g., methane, nitrogen, carbon monoxide)---what we think of as the building blocks of planets. Our understanding of the Kuiper Belt has been limited by the challenges of acquiring high-quality spectroscopy for midsize and small trans-neptunian objects and composition maps of large dwarf planets. NASA's New Horizons mission represents a breakthrough in our understanding of the trans-neptunian population providing a detailed portrait of objects with very different size scales: the 2400-km-diameter dwarf planet Pluto, the midsize ~1200-km-diameter body Charon, and the much smaller Pluto's satellites (e.g., Nix and Hydra) and (486958) 2014 MU69 (hereafter MU69), the latter with an 18 km equivalent spherical diameter. This is the result of two successful flybys: that of Pluto and its moons on July 14th, 2015 (Stern, S. A., Bagenal, F., Ennico, K., et al. 2015, Science, 350, aad1815), and that of MU69 on January 1st, 2019 (Stern, S. A., Weaver, H. A., Spencer, J. R., et al. 2019, Science, 364, aaw9771). We will present an overview of the color and composition of these very diverse bodies in terms of size, evolutionary stage, and dynamical class in the broad context of the physical and chemical properties of other trans-neptunian objects. Comparing and contrasting these objects will shed light on the mechanisms at play during the epoch of planet formation in the Third Zone of the Solar System.
  10. McKinnon, W., Grundy, W., Hamilton, D., et al., 2019, AGUFM, 2019, P42C-05, On the solar nebula origin of (486958) 2014 MU69, a primordial contact binary in the Kuiper belt
    MU69 is a contact binary, and all the data returned from New Horizons are consistent with it being a planetesimal. It is not a product of heliocentric, high-speed collisional evolution. There is no evidence of it having suffered a catastrophic or even a subcatastrophic impact during its lifetime. Nor is there evidence of hierarchical accretion of independent, heliocentric planetesimals, as slow as those collisions may have been in the beginning. Rather, there is strong evidence that its two lobes ("Ultima" and "Thule") came together at an extremely low velocity, on the order of no more than a couple of m/s and possibly much more slowly. Binary formation is a theoretically predicted common outcome in protoplanetary disks when swarms of locally concentrated solids ("pebble clouds") collapse under their own gravity, and plausibly explains the high fraction of binaries among cold classical Kuiper belt objects (KBOs). Cold classical KBO binaries exhibit a range of binary orbital separations, down to the observable limit, so there is no physical reason that tight or even contact binaries could not form in a collapsing pebble cloud. The prominence of bilobate shapes among the short-period comets, which are derived from the scattered disk component of the Kuiper belt, suggests (but does not require) that there is a process that collapses or hardens Kuiper belt binaries. The alignment of the principal axes of the Ultima and Thule lobes is also consistent with tidal coupling between two co-orbiting bodies, prior to a final merger. Our examination of various mechanisms to drive binary mergers in the cold classical Kuiper belt (Kozai-Lidov, BYORP, tides, collisions, gas drag) highlights the potential importance of gas drag while the protosolar nebula is still present. We find the process to be surprisingly effective, because in a gas nebula with a radial pressure gradient the velocity of the gas deviates from the heliocentric Keplerian velocity of the binary. The headwind that the binary feels couples to the motion of the binary pair about its own center of mass. The resulting viscous, Stokes-regime gas drag can collapse MU69-scale co-orbiting binariesas well as smaller, cometary-scale binarieswithin the few-Myr lifetime of the protosolar gas nebula.
  11. Schindler, K., Bosh, A., Levine, S., et al., 2019, AGUFM, 2019, P42C-08, Results from a stellar occultation by KBO Varda
    We present results obtained from a stellar occultation by the classical Kuiper belt object (174567) Varda on 10 September 2018. Varda is a known binary system and among the largest TNOs known today, but has not been studied during an occultation before. Among our collaborators, 24 stations were able to acquire data at the time of the event, of which 15 obtained a clear detection, making this the best-sampled occultation of a TNO to date. As potential stellar duplicity could cause a significant shift of the ground path, we studied the target star in advance through speckle imaging with 'Alopeke at Gemini North. The reconstructed shape is an ellipsoid, which supports Varda's status as a dwarf planet candidate. Albeit slightly smaller, the calculated size is in agreement with the radiometric diameter based on Herschel/PACS FIR measurements. Post-event analysis of the dataset obtained at DCT revealed a faint, unresolved companion or background star very close to the target, which was well under the detection limit of our speckle imager data, but had practically no effect on the predicted path. No atmosphere has been detected. The occultation helped to constrain size and albedo, which in turn helps to better constrain Varda's density.
  12. Dalle Ore, C., Cruikshank, D., Grundy, W., et al., 2019, AGUFM, 2019, P43C-3486, Pluto Refractory Material
    One of Pluto's unexpected discoveries has been the variety of terrains that characterize its surface. This bounty of data has given us the opportunity to investigate the composition of the different regions to compare and contrast the non-icy refractory component(s) of Pluto's surface. The colored materials that are the target of our investigation are thought to originate either from haze deposition, or from ejection from a liquid water sub-crustal reservoir, or from surface irradiation of the hydrocarbon ices. Considering the dynamic nature of Pluto's surface, continually refreshed and/or renewed, the possibility of a primordial component is remote. We compare the refractory material of different regions of Pluto's surface and attempt at identifying their origin.
  13. Schenk, P., Grundy, W., Hansen, C., et al., 2019, AGUFM, 2019, P53D-3492, Triton's Surface Composition: Reevaluation of Voyager colors from the perspective of New Horizons at Pluto
    New Horizons mapping of Pluto the best known Kuiper Belt Object (KBO), revealed the presence of surface ices (including CO, CH4, N2, and H2O) and their geologic distribution. Triton, the largest moon of Neptune, is very similar in size and bulk density to Pluto and was likely a KBO before capture. Both bodies orbit at comparable distances from the Sun (though Pluto goes further out) and have similar rotation periods. Both have complex obliquity cycles and both may have been or are ocean worlds. Triton is also a priority target for future exploration. Voyager (VGR) color mapping lacked the infrared capabilities of New Horizons (NH), rendering compositional mapping very difficult, but also revealed complex geologic and atmospheric color patterns on the surface of Triton. These include color changes at unit boundaries and equatorial bright and dark regional patterns uncorrelated to geology with very strong UV signatures. Small dark spots that appear wind-blown also have distinct spectral signatures. We have remapped the color data for Triton using updated cartography. VGR did extend into the UV which allows comparisons to Cassini icy moons color mapping. Color filter bandpasses for VGR & NH overlap in the 0.4 and 0.6 micron bands, which allows for a comparison of the brightness and spectral slopes of color units on the two bodies. The presence of CO2 on Triton will produce a distinct spectral signature compared to Pluto. Principle component analysis will be updated using all 6 filters to identify distinctive surface components. Disk integrated color rotational coverage from Earth-based spectra may also permit correlation of specific color units with identified longitudinal concentrations of ice phases.
  14. Singer, K., Stern, A., Moore, J., et al., (including Grundy, W.), 2019, AGUFM, 2019, P54B-09, The New Horizons Mission: Pluto and the Kuiper Belt Up-Close
    In July of 2015 the New Horizons spacecraft flew through the Pluto system, initiating humanity's close-up exploration of Kuiper belt objects (Stern et al., 2015, Science). Pluto turned out to be a world of remarkable geologic diversity whose terrains display a range of ages and varied compositions, suggesting geologic activity of various forms (both endogenic and exogenic) has persisted for much of Pluto's history (e.g., Moore et al., 2016, Science). This was a surprise given Pluto's size and lack of recent tidal energy inputs. Many discoveries were also made about Pluto's complex atmosphere, including the existence of many haze layers. Pluto's large moon Charon appears to have had an early large cyrovolcanic resurfacing episode along with large-scale extensional tectonism.

    On January 1 of 2019 New Horizons encountered its second target, a cold classical Kuiper belt object approximately 35 km across at 43 AU (Stern et al., 2019, Science). This is the farthest and most primordial planetary body ever explored in detail. Its flattened, snowperson-like shape and unique surface features are helping us learn about the earliest times in the solar system and how planetary bodies formed (Spencer et al., 2019, Science; McKinnon et al., 2019, Science). No satellites or rings were found. MU69's surface has the signature of H2O and CH3OH (methanol) and a very red color, indicative of other organics.

    This presentation will highlight some of the unique aspects of the Pluto-system, and give an update on the ongoing work to further unveil its secrets. We will also present an overview of what New Horizons is learning about the Kuiper belt as a whole (from Pluto to MU69 to distant KBO observations) and what new information this gives us about planetesimal and planet formation.

  15. Morbidelli, A., Grundy, W., 2019, Icar, 334, 1, Introduction to Icarus special papers on trans-neptunian solar system
    In March 2018, the international community working on the trans-neptunian small body population met in Coimbra for a one-week scientific meeting. It was the sixth of such meetings, starting with the one in Garching in 1998, just six years after the discovery of the first trans-neptunian object besides Pluto: 1992 QB1 by Jewitt and Luu (1993). This special issue of Icarus contains ten papers which report original research results presented at the meeting. A book of review papers associated to the meeting is under finalization and will be published soon by Elsevier.
  16. Kiss, C., Marton, G., Parker, A., et al., (including Grundy, W.), 2019, Icar, 334, 3, The mass and density of the dwarf planet (225088) 2007 OR10
    The satellite of (225088) 2007 OR10 was discovered on archival Hubble Space Telescope images and along with new observations with the WFC3 camera in late 2017 we have been able to determine the orbit. The orbit's notable eccentricity, e 0.3, may be a consequence of an intrinsically eccentric orbit and slow tidal evolution, but may also be caused by the Kozai mechanism. Dynamical considerations also suggest that the moon is small, Deff < 100 km. Based on the newly determined system mass of 1.75 1021 kg, 2007 OR10 is the fifth most massive dwarf planet after Eris, Pluto, Haumea and Makemake. The newly determined orbit has also been considered as an additional option in our radiometric analysis, provided that the moon orbits in the equatorial plane of the primary. Assuming a spherical shape for the primary this approach provides a size of 1230 50 km, with a slight dependence on the satellite orbit orientation and primary rotation rate chosen, and a bulk density of 1.75 0.07 g cm-3 for the primary. A previous size estimate that assumed an equator-on configuration (1535-225+75 km) would provide a density of 0.92-0.14+0.46 g cm-3, unexpectedly low for a 1000 km-sized dwarf planet.
  17. Grundy, W., Noll, K., Buie, M., et al., 2019, Icar, 334, 30, The mutual orbit, mass, and density of transneptunian binary Gkun'homdima (229762 2007 UK126)
    We present high spatial resolution images of the binary transneptunian object Gkun'homdima (229762 2007 UK126) obtained with the Hubble Space Telescope and with the Keck observatory on Mauna Kea to determine the orbit of Go'e huGo'e hu, the much smaller and redder satellite. Go'e hu orbits in a prograde sense, on a circular or near-circular orbit with a period of 11.3 days and a semimajor axis of 6000 km. Tidal evolution is expected to be slow, so it is likely that the system formed already in a low-eccentricity configuration, and possibly also with the orbit plane of the satellite in or close to the plane of Gkun'homdima's equator. From the orbital parameters we can compute the system mass to be 1.4 1020 kg. Combined with estimates of the size of Gkun'homdima from thermal observations and stellar occultations, we can estimate the bulk density as about 1 g cm-3. This low density is indicative of an ice-rich composition, unless there is substantial internal porosity. We consider the hypothesis that the composition is not unusually ice-rich compared with larger TNOs and comet nuclei, and instead the porosity is high, suggesting that mid-sized objects in the 400 to 1000 km diameter range mark the transition between small, porous objects and larger objects that have collapsed their internal void space as a result of their much higher internal pressures and temperatures.
  18. Muller, T., Kiss, C., Ali-Lagoa, V., et al., (including Mommert, M., Thirouin, A.), 2019, Icar, 334, 39, Haumea's thermal emission revisited in the light of the occultation results
    A recent multi-chord occultation measurement of the dwarf planet (136108) Haumea (Ortiz et al., 2017) revealed an elongated shape with the longest axis comparable to Pluto's mean diameter. The chords also indicate a ring around Haumea's equatorial plane, where its largest moon, Hi'iaka, is also located. The Haumea occultation size estimate (size of an equal-volume sphere1 Dequ = 1595 km) is larger than previous radiometric solutions (equivalent sizes in the range between 1150 and 1350 km), which lowers the object's density to about 1.8 g/cm3, a value closer to the densities of other large TNOs. We present unpublished and also reprocessed Herschel and Spitzer mid- and far-infrared measurements. We compare 100 and 160 Am thermal lightcurve amplitudes - originating from Haumea itself - with models of the total measured system fluxes (ring, satellite, Haumea) from 24-350 m. The combination with results derived from the occultation measurements allows us to reinterpret the object's thermal emission. Our radiometric studies show that Haumea's crystalline water ice surface must have a thermal inertia of about 5 J K-1 m-2s-1/2 (combined with a root mean square of the surface slopes of 0.2). We also have indications that the satellites (at least Hi'iaka) must have high geometric albedos 0.5, otherwise the derived thermal amplitude would be inconsistent with the total measured system fluxes at 24, 70, 100, 160, 250, and 350 Am. The high albedos imply sizes of about 300 and 150 km for Hi'iaka and Namaka, respectively, indicating unexpectedly high densities > 1.0 g cm-3 for TNOs this small, and the assumed collisional formation from Haumea's icy crust. We also estimated the thermal emission of the ring for the time period 1980-2030, showing that the contribution during the Spitzer and Herschel epochs was small, but not negligible. Due to the progressive opening of the ring plane, the ring emission will be increasing in the next decade when JWST is operational. In the MIRI 25.5 m band it will also be possible to obtain a very high-quality thermal lightcurve to test the derived Haumea properties.
  19. Grundy, W., Noll, K., Roe, H., et al., 2019, Icar, 334, 62, Mutual orbit orientations of transneptunian binaries
    We present Keplerian orbit solutions for the mutual orbits of 17 transneptunian binary systems (TNBs). For ten of them, the orbit had not previously been known: 60458 2000 CM114, 119979 2002 WC19, 160091 2000 OL67, 160256 2002 PD149, 469514 2003 QA91, 469705 Kagara, 508788 2000 CQ114, 508869 2002 VT130, 1999 RT214, and 2002 XH91. Seven more are systems where the size, shape, and period of the orbit had been published, but new observations have now eliminated the sky plane mirror ambiguity in its orientation: 90482 Orcus, 120347 Salacia-Actaea, 1998 WW31, 1999 OJ4, 2000 QL251, 2001 XR254, and 2003 TJ58. The dynamical masses we obtain from TNB mutual orbits can be combined with estimates of the objects' sizes from thermal observations or stellar occultations to estimate their bulk densities. The Kagara system is currently undergoing mutual events in which one component casts its shadow upon the other and/or obstructs the view of the other. Such events provide valuable opportunities for further characterization of the system. Combining our new orbits with previously published orbits yields a sample of 35 binary orbits with known orientations that can provide important clues about the environment in which outer solar system planetesimals formed, as well as their subsequent evolutionary history. Among the relatively tight binaries, with semimajor axes less than about 5% of their Hill radii, prograde mutual orbits vastly outnumber retrograde orbits. This imbalance is not attributable to any known observational bias. We suggest that this distribution could be the signature of planetesimal formation through gravitational collapse of local density enhancements such as caused by the streaming instability. Wider binaries, with semimajor axes >5% of their Hill radii, are somewhat more evenly distributed between prograde and retrograde orbits, but with mutual orbits that are aligned or anti-aligned with their heliocentric orbits. This pattern could perhaps result from Kozai-Lidov cycles coupled with tidal evolution eliminating high inclination wide binaries.
  20. McNeill, A., Mommert, M., Trilling, D., et al., (including Llama, J., Skiff, B.), 2019, ApJS, 245, 29, Asteroid Photometry from the Transiting Exoplanet Survey Satellite: A Pilot Study
    The Transiting Exoplanet Survey Satellite (TESS) searches for planets transiting bright and nearby stars using high-cadence, large-scale photometric observations. Full frame images provided by the TESS mission include a large number of serendipitously observed main-belt asteroids (MBAs). Due to the cadence of the published full frame images, we are sensitive to periods as long as of order tens of days, a region of phase space that is generally not accessible through traditional observing. This work represents a much less biased measurement of the period distribution in this period range. We have derived rotation periods for 300 MBAs and have partial lightcurves for a further 7277 asteroids, including 43 with periods of P > 100 hr; this large number of slow rotators is predicted by theory. Of these slow rotators we find none requiring significant internal strength to resist rotational reshaping. We find our derived rotation periods to be in excellent agreement with results in the Lightcurve Database for the 55 targets that overlap. Over the nominal two-year lifetime of the mission, we expect the detection of around 85,000 unique asteroids with rotation period solutions for around 6000 asteroids. We project that the systematic analysis of the entire TESS data set will increase the number of known slow-rotating asteroids (period > 100 hr) by a factor of 10. Comparing our new period determinations with previous measurements in the literature, we find that the rotation period of asteroid (2320) Blarney has decreased by at least 20% over the past decade, potentially due to surface activity or subcatastrophic collisions.
  21. Simon, M., Prato, L., 2019, RNAAS, 3, 186, Disk Evolution and Dissipation in the Taurus Star-forming Region
    No abstract found.
  22. D'Ammando, F., Raiteri, C., Villata, M., et al., (including Skiff, B.), 2019, MNRAS, 490, 5300, Investigating the multiwavelength behaviour of the flat spectrum radio quasar CTA 102 during 2013-2017
    We present a multiwavelength study of the flat-spectrum radio quasar CTA 102 during 2013-2017. We use radio-to-optical data obtained by the Whole Earth Blazar Telescope, 15 GHz data from the Owens Valley Radio Observatory, 91 and 103 GHz data from the Atacama Large Millimeter Array, near-infrared data from the Rapid Eye Monitor telescope, as well as data from the Swift (optical-UV and X-rays) and Fermi (-rays) satellites to study flux and spectral variability and the correlation between flux changes at different wavelengths. Unprecedented -ray flaring activity was observed during 2016 November-2017 February, with four major outbursts. A peak flux of (2158 63) 10-8 ph cm-2 s-1, corresponding to a luminosity of (2.2 0.1) 1050 erg s-1, was reached on 2016 December 28. These four -ray outbursts have corresponding events in the near-infrared, optical, and UV bands, with the peaks observed at the same time. A general agreement between X-ray and -ray activity is found. The -ray flux variations show a general, strong correlation with the optical ones with no time lag between the two bands and a comparable variability amplitude. This -ray/optical relationship is in agreement with the geometrical model that has successfully explained the low-energy flux and spectral behaviour, suggesting that the long-term flux variations are mainly due to changes in the Doppler factor produced by variations of the viewing angle of the emitting regions. The difference in behaviour between radio and higher energy emission would be ascribed to different viewing angles of the jet regions producing their emission.
  23. Hannon, S., Lee, J., Whitmore, B., et al., (including Hunter, D.), 2019, MNRAS, 490, 4648, H morphologies of star clusters: a LEGUS study of H II region evolution time-scales and stochasticity in low-mass clusters
    The morphology of H II regions around young star clusters provides insight into the time-scales and physical processes that clear a cluster's natal gas. We study 700 young clusters (10 Myr) in three nearby spiral galaxies (NGC 7793, NGC 4395, and NGC 1313) using Hubble Space Telescope (HST) imaging from LEGUS (Legacy ExtraGalactic Ultraviolet Survey). Clusters are classified by their H morphology (concentrated, partially exposed, no-emission) and whether they have neighbouring clusters (which could affect the clearing time-scales). Through visual inspection of the HST images, and analysis of ages, reddenings, and stellar masses from spectral energy distributions fitting, together with the (U- B), (V - I) colours, we find (1) the median ages indicate a progression from concentrated (3 Myr), to partially exposed (4 Myr), to no H emission (>5 Myr), consistent with the expected temporal evolution of H II regions and previous results. However, (2) similarities in the age distributions for clusters with concentrated and partially exposed H morphologies imply a short time-scale for gas clearing (1 Myr). Also, (3) our cluster sample's median mass is 1000 M, and a significant fraction ( 20{{ per cent}}) contain one or more bright red sources (presumably supergiants), which can mimic reddening effects. Finally, (4) the median E(B - V) values for clusters with concentrated H and those without H emission appear to be more similar than expected (0.18 versus 0.14, respectively), but when accounting for stochastic effects, clusters without H emission are less reddened. To mitigate stochastic effects, we experiment with synthesizing more massive clusters by stacking fluxes of clusters within each H morphological class. Composite isolated clusters also reveal a colour and age progression for H morphological classes, consistent with analysis of the individual clusters.
  24. Li, T., Koposov, S., Zucker, D., et al., (including Kuehn, K.), 2019, MNRAS, 490, 3508, The southern stellar stream spectroscopic survey (S5): Overview, target selection, data reduction, validation, and early science
    We introduce the southern stellar stream spectroscopy survey (S5), an on-going program to map the kinematics and chemistry of stellar streams in the southern hemisphere. The initial focus of S5 has been spectroscopic observations of recently identified streams within the footprint of the dark energy survey (DES), with the eventual goal of surveying streams across the entire southern sky. Stellar streams are composed of material that has been tidally striped from dwarf galaxies and globular clusters and hence are excellent dynamical probes of the gravitational potential of the Milky Way, as well as providing a detailed snapshot of its accretion history. Observing with the 3.9 m Anglo-Australian Telescope's 2-degree-Field fibre positioner and AAOmega spectrograph, and combining the precise photometry of DES DR1 with the superb proper motions from Gaia DR2, allows us to conduct an efficient spectroscopic survey to map these stellar streams. So far S5 has mapped nine DES streams and three streams outside of DES; the former are the first spectroscopic observations of these recently discovered streams. In addition to the stream survey, we use spare fibres to undertake a Milky Way halo survey and a low-redshift galaxy survey. This paper presents an overview of the S5 program, describing the scientific motivation for the survey, target selection, observation strategy, data reduction, and survey validation. Finally, we describe early science results on stellar streams and Milky Way halo stars drawn from the survey. Updates on S5, including future public data releases, can be found at http://s5collab.github.io.
  25. Martinez-Vazquez, C., Vivas, A., Gurevich, M., et al., (including Kuehn, K.), 2019, MNRAS, 490, 2183, Search for RR Lyrae stars in DES ultrafaint systems: Grus I, Kim 2, Phoenix II, and Grus II
    This work presents the first search for RR Lyrae stars (RRLs) in four of the ultrafaint systems imaged by the Dark Energy Survey using SOAR/Goodman and Blanco/DECam imagers. We have detected two RRLs in the field of Grus I, none in Kim 2, one in Phoenix II, and four in Grus II. With the detection of these stars, we accurately determine the distance moduli for these ultrafaint dwarf satellite galaxies; 0 = 20.51 0.10 mag (D = 127 6 kpc) for Grus I and 0 = 20.01 0.10 mag (D = 100 5 kpc) for Phoenix II. These measurements are larger than previous estimations by Koposov et al. and Bechtol et al., implying larger physical sizes; 5 per cent for Grus I and 33 per cent for Phoenix II. For Grus II, of the four RRLs detected, one is consistent with being a member of the galactic halo (D = 24 1 kpc, 0 = 16.86 0.10 mag), another is at D = 55 2 kpc (0 = 18.71 0.10 mag), which we associate with Grus II, and the two remaining at D = 43 2 kpc (0 = 18.17 0.10 mag). Moreover, the appearance of a subtle red horizontal branch in the colour-magnitude diagram of Grus II at the same brightness level of the latter two RRLs, which are at the same distance and in the same region, suggests that a more metal-rich system may be located in front of Grus II. The most plausible scenario is the association of these stars with the Chenab/Orphan Stream. Finally, we performed a comprehensive and updated analysis of the number of RRLs in dwarf galaxies. This allows us to predict that the method of finding new ultrafaint dwarf galaxies using two or more clumped RRLs will work only for systems brighter than MV -6 mag.
  26. Noll, K., Brown, M., Buie, M., et al., (including Grundy, W.), 2019, hst, 16056, Recovery and Orbit of a Satellite of the Trojan Asteroid Eurybates - a Lucy Mission Target
    A deep search for satellites around Jupiter Trojan asteroids that are targets of NASA's Lucy mission has yielded the detection of a small satellite with d<~1km orbiting Eurybates. Observations on 12 and 14 September 2018 show a V~26.77 mag object at a projected distance of 1928 km from Eurybates that is moving at a rate consistent with that of a bound satellite. The Lucy spacecraft is planned to fly within this distance to a close approach of 1000+/-75 km. Thus, it is of critical importance to the mission to recover the satellite and constrain the orbit in order to evaluate the impact on the design of targeting, flyby, and science sequences, data volume, and other potential effects. We are requesting immediate observations prior to 11 January 2020 for recovery and initial orbit characterization with more detailed orbit determination observations during the next very favorable opposition starting in September 2020.
  27. Moskovitz, N., Fatka, P., Farnocchia, D., et al., (including Devogele, M., Mommert, M., Burt, B., Skiff, B., Thirouin, A., Wasserman, L.), 2019, Icar, 333, 165, A common origin for dynamically associated near-Earth asteroid pairs
    Though pairs of dynamically associated asteroids in the Main Belt have been identified and studied for over a decade, very few pair systems have been identified in the near-Earth asteroid population. We present data and analysis that supports the existence of two genetically related pairs in near-Earth space. The members of the individual systems, 2015 EE7 - 2015 FP124 and 2017 SN16 - 2018 RY7, are found to be of the same spectral taxonomic class, and both pairs are interpreted to have volatile-poor compositions. In conjunction with dynamical arguments, this suggests that these two systems formed via YORP spin-up and/or dissociation of a binary precursor. Backwards orbital integrations suggest a separation age of <10 kyr for the pair 2017 SN16 - 2018 RY7, making these objects amongst the youngest multiple asteroid systems known to date. A unique separation age was not realized for 2015 EE7 - 2015 FP124 due to large uncertainties associated with these objects' orbits. Determining the ages of such young pairs is of great value for testing models of space weathering and asteroid spin-state evolution. As the NEO catalog continues to grow with current and future discovery surveys, it is expected that more NEO pairs will be found, thus providing an ideal laboratory for studying time dependent evolutionary processes that are relevant to asteroids throughout the Solar System.
  28. Pravec, P., Fatka, P., Vokrouhlicky, D., et al., (including Moskovitz, N., Thirouin, A., Skiff, B.), 2019, Icar, 333, 429, Asteroid pairs: A complex picture
    We studied a sample of 93 asteroid pairs, i.e., pairs of genetically related asteroids that are on highly similar heliocentric orbits. We estimated times elapsed since separation of pair members (i.e., pair age) that are between 7 103 yr and a few 106 yr. With photometric observations, we derived the rotation periods P1 for all the primaries (i.e., the larger members of asteroid pairs) and a sample of secondaries (the smaller pair members). We derived the absolute magnitude differences of the studied asteroid pairs that provide their mass ratios q. For a part of the studied pairs, we refined their WISE geometric albedos and collected or estimated their taxonomic classifications. For 17 asteroid pairs, we also determined their pole positions. In two pairs where we obtained the spin poles for both pair components, we saw the same sense of rotation for both components and constrained the angles between their original spin vectors at the time of their separation. We found that the primaries of 13 asteroid pairs in our sample are actually binary or triple systems, i.e., they have one or two bound, orbiting secondaries (satellites). As a by-product, we found also 3 new young asteroid clusters (each of them consisting of three known asteroids on highly similar heliocentric orbits). We compared the obtained asteroid pair data with theoretical predictions and discussed their implications. We found that 86 of the 93 studied asteroid pairs follow the trend of primary rotation period vs mass ratio that was found by Pravec et al. (2010). Of the 7 outliers, 3 appear insignificant (may be due to our uncertain or incomplete knowledge of the three pairs), but 4 are high mass ratio pairs that were unpredicted by the theory of asteroid pair formation by rotational fission. We discuss a (remotely) possible way that they could be created by rotational fission of flattened parent bodies followed by re-shaping of the formed components. The 13 asteroid pairs with binary primaries are particularly interesting systems that place important constraints on formation and evolution of asteroid pairs. We present two hypotheses for their formation: The asteroid pairs having both bound and unbound secondaries could be "failed asteroid clusters", or they could be formed by a cascade primary spin fission process. Further studies are needed to reveal which of these two hypotheses for formation of the paired binary systems is real.
  29. Devogele, M., Moskovitz, N., Thirouin, A., et al., (including Mommert, M., Burt, B., Skiff, B.), 2019, AJ, 158, 196, Visible Spectroscopy from the Mission Accessible Near-Earth Object Survey (MANOS): Taxonomic Dependence on Asteroid Size
    The Mission Accessible Near-Earth Object Survey (MANOS) aims to observe and characterize small (mean absolute magnitude H 25 mag) Near-Earth Objects (NEOs) that are accessible by spacecraft (mean v 5.7 km s-1) and that make close approaches with the Earth (mean Minimum Orbital Intersection Distance MOID 0.03 au). We present here the first results of the MANOS visible spectroscopic survey. The spectra were obtained from August 2013 to March 2018 at Lowell Observatorys Discovery Channel 4.3 m telescope, and both Gemini North and South facilities. In total, 210 NEOs have been observed and taxonomically classified. Our taxonomic distribution shows significant variations with respect to surveys of larger objects. We suspect these to be due to a dependence of Main Belt source regions on object size. Compared to previous surveys of larger objects, we report a lower fraction of S+Q-complex asteroids of 43.8 4.6%. We associate this decrease with a lack of Phocaea family members at very small size. We also report higher fractions of X-complex and A-type asteroids of 23.8 3.3% and 3.8 1.3% respectively due to an increase of Hungaria family objects at small size. We find a strong correlation between the Q/S ratio and perihelion distance. We suggest this correlation is due to planetary close encounters with Venus playing a major role in turning asteroids from S to Q-type. This hypothesis is supported by a similar correlation between the Q/S ratio and Venus MOID.
  30. Shipp, N., Li, T., Pace, A., et al., (including Kuehn, K.), 2019, ApJ, 885, 3, Proper Motions of Stellar Streams Discovered in the Dark Energy Survey
    We cross-match high-precision astrometric data from Gaia DR2 with accurate multiband photometry from the Dark Energy Survey (DES) DR1 to confidently measure proper motions for nine stellar streams in the DES footprint: Aliqa Uma, ATLAS, Chenab, Elqui, Indus, Jhelum, Phoenix, Tucana III, and Turranburra. We determine low-confidence proper-motion measurements for four additional stellar streams: Ravi, Wambelong, Willka Yaku, and Turbio. We find evidence for a misalignment between stream tracks and the systemic proper motion of streams that may suggest a systematic gravitational influence from the Large Magellanic Cloud (LMC). These proper motions, when combined with radial velocity measurements, will allow for detailed orbit modeling that can be used to constrain properties of the LMC and its effect on nearby streams, as well as global properties of the Milky Ways gravitational potential.
  31. Cale, B., Plavchan, P., LeBrun, D., et al., (including von Braun, K.), 2019, AJ, 158, 170, Precise Radial Velocities of Cool Low-mass Stars with iSHELL
    The coolest dwarf stars are intrinsically faint at visible wavelengths and exhibit rotationally modulated stellar activity from spots and plages. It is advantageous to observe these stars at near-infrared (NIR) wavelengths (1-2.5 m) where they emit the bulk of their bolometric luminosity and are most quiescent. In this work, we describe our methodology and results in obtaining precise radial velocity (RV) measurements of low-mass stars using K-band spectra taken with the R 80,000 iSHELL spectrograph and the NASA Infrared Telescope Facility using a methane isotopologue gas cell in the calibration unit. Our novel analysis pipeline extracts RVs by minimizing the rms of the residuals between the observed spectrum and a forward model. The model accounts for the gas cell, tellurics, blaze function, multiple sources of quasi-sinusoidal fringing, and line spread function of the spectrograph. The stellar template is derived iteratively using the target observations themselves through averaging barycenter-shifted residuals. We have demonstrated 5 m s-1 precision over one-year timescales for the M4 dwarf Barnards Star and K dwarf 61 Cygni A, and 3 m s-1 over a month for the M2 dwarf GJ 15 A. This work demonstrates the potential for iSHELL to determine dynamical masses for candidate exoplanets discovered with the NASA Transiting Exoplanet Survey Satellite mission, and to search for exoplanets orbiting moderately active and/or young K & M dwarfs.
  32. Gregg, M., West, M., 2019, hst, 16025, Snapshot Survey of the Globular Cluster Populations of Isolated Early Type Galaxies
    We propose WFC3/UVIS snapshot observations of a sample of 75 isolated early type galaxies residing in cosmic voids or extremely low density regions. The primary aim is to use their globular cluster populations to reconstruct their evolutionary history, revealing if, how, and why void ellipticals differ from cluster ellipticals. The galaxies span a range of luminosities, providing a varied sample for comparison with the well-documented globular cluster populations in denser environments. This proposed WFC3 study of isolated early type galaxies breaks new ground by targeting a sample which has thus far received little attention, and, significantly, this will be the first such study with HST. Characterizing early type galaxies in voids and their GC systems promises to increase our understanding of galaxy formation and evolution of galaxies in general because isolated objects are the best approximation to a control sample that we have for understanding the influence of environment on formation and evolution. Whether these isolated objects turn out to be identical to or distinct from counterparts in other regions of the Universe, they will supply insight into the formation and evolution of all galaxies. Parallel ACS imaging will help to characterize the near field environments of the sample.
  33. Davis, B., Bond, H., Ciardullo, R., et al., (including Jacoby, G.), 2019, ApJ, 884, 115, Hubble Space Telescope Spectroscopy of a Planetary Nebula in an M31 Open Cluster: Hot-bottom Burning at 3.4 M
    We use imaging and spectroscopy from the Hubble Space Telescope (HST) to examine the properties of a bright planetary nebula (PN) projected within M31's young open cluster B477-D075. We show that the probability of a chance superposition of the PN on the cluster is small, 2%. Moreover, the radial velocity of the PN is the same as that of the cluster within the measurement error of 10 km s-1. Given the expected 70 km s-1 velocity dispersion in this region, 8 kpc from M31's nucleus, the velocity data again make it extremely likely that the PN belongs to the cluster. Applying isochrone fitting to archival color-magnitude photometric data from the HST Advanced Camera for Surveys, we determine the cluster age and metallicity to be 290 Myr and Z = 0.0071, respectively, implying an initial mass of {3.38}-0.02+0.03 {M} for any PN produced by the cluster. From HSTs Space Telescope Imaging Spectrograph observations and CLOUDY photoionization modeling, we find that the PN is likely a Type I planetary, with a nitrogen abundance that is enhanced by 5-6 times over the solar value scaled to the cluster metallicity. If the PN is indeed a cluster member, these data present strong empirical evidence that hot-bottom burning occurs in asymptotic giant branch stars with initial masses as low as 3.4 M .

    Based on observations with the NASA/ESA Hubble Space Telescope obtained at Space Telescope Science Institute, operated by Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

  34. Sullivan, K., Prato, L., Edwards, S., et al., (including Avilez, I.), 2019, ApJ, 884, 28, S and VV Corona Australis: Spectroscopic Variability in Two Young Binary Star Systems
    We used high-resolution near-infrared spectroscopy from the NIRSPEC instrument on the Keck II telescope, taken over multiple epochs spanning five years, to examine two young binary T Tauri star systems, S Corona Australis and VV Corona Australis. The stars in these 1-2 separation systems have optically thick circumstellar disks and high extinctions at optical and near-infrared wavelengths. Using a combination of new and archival data, we have determined the spectral types of all of the stars in these two systems for the first time, examined the variable NIR veiling, measured the emission line equivalent widths, and created spectral energy distributions. They have similar spectral types (K7-M1) and are at approximately the same evolutionary stage, allowing for comparison of the four stars in the two systems. We conclude that S CrA and VV CrA are young binary systems of stars bridging the Class I and Class II evolutionary stages, characterized by high accretion luminosities and variable emission lines.
  35. Simon, M., Guilloteau, S., Beck, T., et al., (including Prato, L.), 2019, ApJ, 884, 42, Masses and Implications for Ages of Low-mass Pre-main-sequence Stars in Taurus and Ophiuchus
    The accuracy of masses of pre-main-sequence stars derived from their locations on the Hertzsprung-Russell diagram (HRD) can be tested by comparison with accurate and precise masses determined independently. We present 29 single stars in the Taurus star-forming region (SFR) and 3 in the Ophiuchus SFR with masses measured dynamically to a precision of at least 10%. Our results include 9 updated mass determinations and 3 that have not had their dynamical masses published before. This list of stars with fundamental, dynamical masses, M dyn, is drawn from a larger list of 39 targets in the Taurus SFR and 6 in the Ophiuchus SFR. Placing the stars with accurate and precise dynamical masses on HRDs that do not include internal magnetic fields underestimates the mass compared to M dyn by about 30%. Placing them on an HRD that does include magnetic fields yields mass estimates in much better agreement with M dyn, with an average difference between M dyn and the estimated track mass of 0.01 0.02 M . The ages of the stars, 3-10 MY on tracks that include magnetic fields, is older than the 1-3 MY indicated by the nonmagnetic models. The older ages of T Tauri stars predicted by the magnetic models increase the time available for evolution of their disks and formation of the giant gas exoplanets. The agreement between our M dyn values and the masses on the magnetic field tracks provides indirect support for these older ages.
  36. Kammer, J., Becker, T., Retherford, K., et al., (including Wasserman, L.), 2019, AJ, 158, 168, Probing the Hill Sphere of (486958) 2014 MU69. II. Hubble Space Telescope Fine Guidance Sensors Observations during the 2018 August 4 Stellar Occultation
    We observed the 2018 August 4 stellar occultation by the Kuiper Belt object (486958) 2014 MU69, the first close flyby target of the extended New Horizons mission. Rather than capture a solid-body occultation by the KBO itself, our program aimed to constrain the opacity of rings, moons, or other debris in the nearby environment. We used the Hubble Space Telescope Fine Guidance Sensors (HST FGS) instrument in TRANS F583W mode to collect 40 Hz time resolution photometry of the stellar occultation star for one HST orbit during this observation. We present the results of reduction and calibration of the HST FGS photometry, and set upper limits on of 0.02-0.08 for rings or other dust opacity within the Hill sphere of (486958) 2014 MU69 at distances ranging from 1660 to 57,700 km from the main body.
  37. Cook, J., Dalle Ore, C., Protopapa, S., et al., (including Grundy, W., Hanley, J.), 2019, Icar, 331, 148, The distribution of H2O, CH3OH, and hydrocarbon-ices on Pluto: Analysis of New Horizons spectral images
    On July 14, 2015, the New Horizons spacecraft made its closest approach to Pluto at about 12,000 km from its surface (Stern et al., 2015). Using the LEISA (Linear Etalon Imaging Spectral Array) near-IR imaging spectrometer we obtained two scans across the encounter hemisphere of Pluto at 6-7 km/pixel resolution. By correlating each spectrum with a crystalline H2O-ice model, we find several sites on Pluto's surface that exhibit the 1.5, 1.65 and 2.0 m absorption bands characteristic of H2O-ice in the crystalline phase. These sites tend to be isolated and small ( 5000 km2 per site). We note a distinct near-IR blue slope over the LEISA wavelength range and asymmetries in the shape of the 2.0 m H2O-ice band in spectra with weak CH4-ice bands and strong H2O-ice bands. These characteristics are indicative of fine-grain (grain diameters < wavelength or 1 m) H2O-ice, like that seen in the spectra of Saturnian rings and satellites. However, the best-fit Hapke models require small mass fractions (10-3) of fine-grained H2O-ice that we can exchange for other refractory materials in the models with little change in 2, which may mean that the observed blue slope is possibly not due to a fine-grained material but an unidentified material with a similar spectral characteristic. We use these spectra to test for the presence of amorphous H2O-ice and estimate crystalline-to-amorphous H2O-ice fractions between 30 and 100%, depending on the location. We also see evidence for heavy hydrocarbons via strong absorption at > 2.3 m. Such heavy hydrocarbons are much less volatile than N2, CH4, and CO at Pluto temperatures. We test for CH3OH, C2H6, C2H4, and C3H8-ices because they have known optical constants and these ices are likely to arise from UV and energetic particle bombardment of the N2, CH4, CO-rich surface and atmosphere. Finally, we attempt to estimate the surface temperature using optical constants of pure CH4, and H2O-ice and best-fit Hapke models. Our standard model gives temperature estimates between 40 and 90 K, while our models including amorphous H2O-ice give lower temperature estimates between 30 and 65 K.
  38. Moore, J., McKinnon, W., Spencer, J., et al., (including Grundy, W.), 2019, EPSC, 2019, EPSC-DPS2019-50, Scarp Retreat on MU69: Evidence and Implications for Composition and Structure
    Crenulated scarps and other unit boundary patterns are consistent with scarp retreat. If indeed scarps have retreated on MU69 the most likely process is sublimation degradation. This explanation has implications for both original volatile composition and structure (layering) of MU69.
  39. Erasmus, N., McNeill, A., Mommert, M., et al., 2019, EPSC, 2019, EPSC-DPS2019-147, Investigating Taxonomic Diversity of the Main Belt through KMTNET-SAAO and ATLAS Multi-band Photometry
    We present multi-band photometry from the South Africa node of the Korea Microlensing Telescope Network (KMTNet-SAAO) and the Asteroid Terrestrial-impact Last Alert System (ATLAS) which we use to classify several thousand main-belt asteroids with the Bus-DeMeo taxonomic scheme. We use our determined taxonomies to investigating the taxonomic diversity of the Main Belt and in particular the diversity observed in the Flora family.
  40. Dalle Ore, C., Cruikshank, D., Protopapa, S., et al., (including Grundy, W.), 2019, EPSC, 2019, EPSC-DPS2019-207, Pluto dark refractory material: a close look at composition and origin
    We examine a few regions of interest (ROIs) from the high spatial resolution scan obtained with the Linear Etalon Imaging Spectral Array (LEISA) during the July 2015 New Horizons Pluto flyby. We focus on the dark material that distinguishes the equatorial region known as Cthulhu and compare and contrast its signature as the H2O component varies in either abundance or grain size. Our goal is to trace the origin of the material and constrain its mechanisms of formation.
  41. Porter, S., Beyer, R., Keane, J., et al., (including Grundy, W.), 2019, EPSC, 2019, EPSC-DPS2019-311, The Shape and Pole of (486958) 2014 MU69
    NASA's New Horizons spacecraft flew past the cold classical Kuiper Belt Object (KBO) 2014 MU69, providing the first opportunity to see a KBO up close. We will present our initial results on the shape and pole fitting of MU69, showing its contact-binary shape, highly-inclined pole, and the implications for KBO formation.
  42. McNeill, A., Mommert, M., Trilling, D., et al., (including Llama, J.), 2019, EPSC, 2019, EPSC-DPS2019-318, Asteroid Photometry from the Transiting Exoplanet Survey Satellite
    We present photometric measurements for main belt asteroids (MBAs) measured by the Transiting Exoplanet Survey Satellite (TESS). TESS data provides a unique opportunity to measure the how the brightness of thousands of asteroids change continuously for twenty-seven days and is the first data set to allow a probe of long asteroid rotation periods. We present a sample of the 300 constrained rotation periods and 6600 partial light curves obtained from Sectors 1+2 of the TESS Public Data Release, allowing us to learn about the shapes and rotational properties of these objects. We aim to continue this project through the mission lifetime of TESS and expect to obtain 4000 rotation periods and partial data for a further 48000 asteroids.
  43. Sanchez, J., Reddy, V., Thirouin, A., et al., 2019, EPSC, 2019, EPSC-DPS2019-344, Characterization of Active Asteroid (6478) Gault
    Here we report the results from our rotational and spectral characterization of main belt active asteroid (6478) Gault. Based on three nights of observations, we could not confirm the rotation period of 2 h for Gault reported in previous work, as no obvious variability in the lightcurves was found. NIR spectroscopic data obtained with the IRTF showed a spectrum similar to that of S-type asteroids, and a composition consistent with H chondrite meteorites. These results favor a compositional affinity between Gault and the Phocaea family.
  44. Trilling, D., Gerdes, D., Trujillo, C., et al., (including Mommert, M.), 2019, EPSC, 2019, EPSC-DPS2019-395, The Deep Ecliptic Exploration Project (DEEP): A new NOAO survey of the faint outer Solar System
    We have begun a new survey progam to carry out a deep search of the faint outer Solar System with the Dark Energy Camera and the 4-meter Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile. We will measure the size distribution and physical properties of 5000 very faint Kuiper Belt Objects (KBOs). We will measure the size distribution, colors, and shape distribution of KBOs as a function of their orbital properties. Our data set will also allow us to measure the colors, size distribution, and shape distribution of main belt asteroids, and enable a rich array of other science investigations. Our results will help elucidate the composition and structure of the outer Solar System and the origin of our planetary system.
  45. Bird, M., Linscott, I., Hinson, D., et al., (including Grundy, W.), 2019, EPSC, 2019, EPSC-DPS2019-413, New Horizons REX Radiometry at Pluto and Charon
    The thermal radio emission at 4.2 cm from Pluto and Charon was measured by radiometry observations as part of the REX investigation on New Horizons. As expected from its higher optical albedo, Charon was determined to be distinctly warmer than Pluto. The thermal emission from the dayside of both bodies was found to be stronger than on the nightside.
  46. Olkin, C., Stern, S., Spencer, J., et al., (including Grundy, W.), 2019, EPSC, 2019, EPSC-DPS2019-639, The Color of 2014 MU69 from New Horizons
    This paper presents the color of MU69.
  47. Moskovitz, N., Schottland, R., Burt, B., et al., (including Wasserman, L., Mommert, M.), 2019, EPSC, 2019, EPSC-DPS2019-644, Modernizing Lowell Observatory's astorb Database
    The astorb database is an actively currated catalog of orbits for all known asteroids in the Solar System. The full catalog is downloadable from Lowell Observatory and VizieR. The data in astorb are used to support a number of observational planning tools hosted at astetoid.lowell.edu. Since 2016 we have been funded by NASA to modernize both the underlying database infrastructure and the front-end web applications. We will present an overview of the current astorb ecosystem and plans for future development.
  48. Moskovitz, N., Fatka, P., Farnocchia, D., et al., (including Devogele, M., Mommert, M., Thirouin, A.), 2019, EPSC, 2019, EPSC-DPS2019-650, A common origin for dynamically associated near-Earth asteroid pairs
    We present analysis that supports the existence of two genetically related asteroid pairs in near-Earth space. This work suggests that these systems formed via radiative spin-up and fission, and/or dissociation of a binary asteroid. Backwards orbital integrations suggest a separation age of <10 kyr for one of these pairs, making it one of the youngest multiple asteroid systems known to date. As the NEO catalog grows with current and future discovery surveys, the known population of NEO pairs will also increase.
  49. Thirouin, A., Sheppard, S., 2019, EPSC, 2019, EPSC-DPS2019-657, Contact binaries in the trans-Neptunian population: location, physical and rotational properties.
    We are searching for and characterizing contact binaries in the trans-Neptunian populations through an extensive survey with the 4.3 m Lowell's Discovery Channel Telescope and the 6.5 m Magellan-Baade telescope. We aim to derive their rotational and physical properties, to constrain their fractions in several sub-populations of trans-Neptunian objects, understand their formation and evolution as well as improve our knowledge of the binary population and by extension the entire trans-Neptunian belt
  50. Devogele, M., Moskovitz, N., Thomas, C., et al., 2019, EPSC, 2019, EPSC-DPS2019-694, The Mission Accessible Near-Earth Objects Survey (MANOS): taxonomic distribution of sub-kilometer NEOs
    The Mission Accessible Near-Earth Objects Survey (MANOS) is a new generation of surveys aiming to observe and characterize sub-kilometer newly discovered Near-Earth Objects (NEOs). This survey began in August 2013 and has been collecting astrometry, photometry, and reflectance spectra of this under-studied category of the NEO population. We have determined the taxonomic type of 210 asteroids with a mean size around 60 meters and as small as a few meters. This is the first comprehensive dataset for spectroscopically classified NEOs smaller than 100 meters. In the MANOS dataset, we find the population of small NEOs differ in composition from the population of larger ones. We believed this variation is due to the fact that NEOs originate from different source regions in the Main Belt. Each of these source regions have a different delivery rate efficiency as a function of object size.
  51. Schleicher, D., Knight, M., Farnham, T., et al., 2019, EPSC, 2019, EPSC-DPS2019-740, Narrowband Observations of Comet 46P/Wirtanen During its Exceptional Apparition of 2018/19: Photometry, Jet Morphology, and Modeling Results
    An extensive observing campaign was successfully conducted for Comet 46P/Wirtanen during its excellent recent apparition of 2018/19 using several telescopes at Lowell Observatory. Gas and dust production rates were determined throughout the apparition, while narrowband imaging was obtained over a three-month interval. Two CN gas jets were detected, and modeling of these jets is on-going.
  52. Umurhan, O., Keane, J., Porter, S., et al., (including Grundy, W.), 2019, EPSC, 2019, EPSC-DPS2019-749, Near surface temperature modelling of 2014 MU_69
    New Horizons REX radiometer observed of the small Kuiper Belt Object 2014 MU69 at relatively high phase angle and measured a disk averaged brightness temperature of about 23 K. In this study, we perform a thermophysical analysis of the body to better understand this radio observation. We find for assumed thermophysical parameters, the REX radiometer may have been observing about 0.5 meters beneath MU69's surface.
  53. Parker, A., Porter, S., Kavelaars, J., et al., (including Grundy, W.), 2019, EPSC, 2019, EPSC-DPS2019-768, The Solar System Origins Legacy Survey: Motivation, Design, and Initial Results
    The Solar System Origins Legacy Survey (SSOLS) is a very large Hubble Space Telescope program designed to test predictions about the formation and evolution of primordial planetesimals. It will do this by conducting a carefully calibrated search for binary systems in the Cold Classical Kuiper Belt, with over 200 objects to be observed.
  54. Devogele, M., Moskovitz, N., 2019, EPSC, 2019, EPSC-DPS2019-841, SPECTROSCOPYPIPELINE: multi-instrument python-based pipeline for long-slit asteroid visible spectroscopy reduction
    SPECTROSCOPYPIPELINE (SP) is a pipeline dedicated to the reduction of long-slit visible spectroscopic data. The pipeline can perform reduction of any spectroscopic data, but has been primarily developed and optimized for complete reduction of asteroid spectroscopic observation. It is a python-based open source pipeline intended to be easily portable to any long-slit spectrometer. It currently supports both Gemini North and South GMOS instruments, Lowell Observatory's 4.3m Discovery Channel Telescope DeVeny spectrograph and the SOAR 4.1m Goodman spectrograph.
  55. Beyer, R., Porter, S., Schenk, P., et al., (including Grundy, W.), 2019, EPSC, 2019, EPSC-DPS2019-849, Stereo Topography of KBO (486958) 2014 MU69
    We describe stereo topography of KBO MU69. We detail the New Horizons observations that were used to produce the topography, characteristics of the resulting model, and its relation to the whole body shape model derived by other means.
  56. Fayolle, M., Quirico, E., Schmitt, B., et al., (including Grundy, W.), 2019, EPSC, 2019, EPSC-DPS2019-876, Testing tholins as analogs of the dark reddish material covering the cthulhu region.
    We report on the determination of the optical properties of dusty tholins, which have been used in Hapke models to fit MVIC/LEISA data collected by the New Horizons spacecraft. We show a mismatch between models and observations, which is best explained by the presence of a highly porous organic material.
  57. Delbo, M., Walsh, K., Avdellidou, C., et al., (including Van Belle, G.), 2019, EPSC, 2019, EPSC-DPS2019-877, The search for the most ancient asteroid collisions reveals the original planetesimals of our solar system
    Hundred years of asteroid family research and new asteroid family identification methods have shed new light on the collisions among asteroids that shaped the main belt. In particular, in the inner portion of the belt - bracketed by the nu6 secular resonance at 2.1 au and by the J:3/1 mean motion resonance at 2.5 au - it is now possible to distinguish those asteroids that formed as collisional fragments from the break up of larger and older parents, and those other that are not fragments. This second population, which constitutes those asteroids that formed as planetsiamals by the accretion of dust in the protoplanetary disk, has a size distribution skewed towards bodies with diameters larger than 50 km. This indicates that planetesimals formed big, as previously suggested.
  58. Spencer, J., Grundy, W., Schmidt, C., 2019, EPSC, 2019, EPSC-DPS2019-935, Rapid Temporal Variability of Condensed Oxygen on Europa?
    New visible-wavelength spectroscopy of Europa provides the best view so far of the enigmatic 0.3% deep 5770 A absorption feature due to condensed O2. The band depth is inconsistent in observations of the same longitude on Europa taken a week apart, which if real implies surprisingly rapid temporal variability. Additional observations are being obtained to further test the reality of these rapid changes.
  59. Gabasova, L., Blanchard, N., Schmitt, B., et al., (including Grundy, W.), 2019, EPSC, 2019, EPSC-DPS2019-968, Pluto surface composition from spectral model inversion with metaheuristics
    We present first quantitative results for the composition of Pluto's surface from New Horizons LEISA data, achieved using radiative transfer model inversion via progressive metaheuristic methods. We discuss the implications of these results as regards other New Horizons datasets for Pluto's surface, and introduce new methods for pixel-by-pixel mapping and segmentation in order to create a global quantitative compositional map.
  60. Young, L., Tan, S., Trafton, L., et al., (including Grundy, W.), 2019, EPSC, 2019, EPSC-DPS2019-1015, Atmosphere/Surface/Subsurface Interaction at Pluto
    Methane is critical to Pluto's evolution. The methane in Pluto's atmosphere, surface, and subsurface is not in equilibrium. If we understand how and why now, we can extrapolate behavior to other epochs.
  61. Protopapa, S., Olkin, C., Grundy, W., et al., 2019, EPSC, 2019, EPSC-DPS2019-1026, Photometric properties of Pluto's main surface units
    We present a multi-wavelength, regionally dependent photometric analysis of Pluto's surface. We will perform a comparative analysis and use these properties to quantitively infer the composition of Pluto's different terrains and investigate the different coloring agents across Pluto's surface.
  62. Knight, M., Farnham, T., Schleicher, D., et al., (including Schindler, J., Skiff, B.), 2019, EPSC, 2019, EPSC-DPS2019-1035, Narrowband Observations of Comet 46P/Wirtanen During its Exceptional Apparition of 2018/19: Gas Jet Morphology and Rotation Period
    An extensive observing campaign was successfully conducted for Comet 46P/Wirtanen during its excellent recent apparition of 2018/19 using several telescopes at Lowell Observatory. Narrowband imaging was obtained over a three-month interval, revealing two CN gas jets throughout the apparition. Their motion and repetition allowed us to determine a rotation period near 9 hr in early November. We continued to obtain sufficient data to constrain the rotation period through early February and detect little to no change. We see no rotational variation in dust images. C3 exhibits a similar morphology to CN, while OH shows a different spatial distribution. Analyses are ongoing and new results will be presented.
  63. Prato, L., Johns-Krull, C., Llama, J., et al., (including Nofi, L., Biddle, L., Skiff, B.), 2019, EPSC, 2019, EPSC-DPS2019-1078, Finding the Youngest Exoplanets
    In spite of the diverse wealth of data provided by the identification of thousands of planets spanning a broad parameter space, we know little about young (less than a few Myr old) planets. To advance our understanding of the processes governing planet formation and evolution, we need to find and characterize young planets themselves. Given the extreme activity inherent in young stars, particularly those with active, primordial accretion disks, this is a challenging undertaking. We describe our search for young exoplanets and recent results.
  64. Hanley, J., Engle, A., Dustrud, S., et al., (including Grundy, W.), 2019, EPSC, 2019, EPSC-DPS2019-1146, Understanding the Hydrocarbon Lakes and Seas on Titan
    We have performed laboratory experiments and chemical modeling to understand methane and ethane stability in the presence of a nitrogen atmosphere with respect to surface condition on Titan.
  65. Gustafsson, A., Moskovitz, N., Protopapa, S., et al., (including Schleicher, D.), 2019, EPSC, 2019, EPSC-DPS2019-1179, Water-Ice Distribution in the Coma of 46P/Wirtanen
    Comet 46P/Wirtanen made a close approach to the Earth in December 2018 (geocentric distance=0.077 au ; heliocentric distance=1.056 au), providing a unique opportunity to collect spatially resolved spectral observations. We created a near-infrared spectral data cube near close approach to better understand the water-ice grain properties of the comet coma.
  66. Gustafsson, A., Moskovitz, N., Roe, H., et al., (including Bida, T.), 2019, EPSC, 2019, EPSC-DPS2019-1190, The Near-Infrared High Throughput Spectrograph
    NIHTS is a low resolution near-infrared spectrograph on the Discovery Channel Telescope in Happy Jack, AZ, USA. NIHTS has been fully operational since March of 2018. The instrument will enable many science use cases, including investigations into water-ice in Kuiper Belt Objects and comets, and classification of Near-Earth asteroids and ultracool brown dwarfs.
  67. Throop, H., Lauer, T., Spencer, J., et al., (including Grundy, W.), 2019, EPSC, 2019, EPSC-DPS2019-1196, Limits on Rings and Debris Around 2014 MU69 from New Horizons
    We searched for rings around 2014MU69 ('Ultima Thule'). We looked extensively, but we found nothing.
  68. Fraser, W., Schwamb, M., Bannister, M., et al., (including Thirouin, A.), 2019, EPSC, 2019, EPSC-DPS2019-1206, Col-OSSOS: A Compositional Interpretation of Kuiper Belt Spectra
    We propose a new compositional model for Kuiper Belt Objects that can account for many of the observed properties of those bodies, including their colour, and spectral behaviour. This model successfully accounts for the links to other related bodies, including the satellite Phoebe. The model asserts that the majority of KBOs consist of reddened carbonaceous material. If true, this implies that neutral class KBOs share a primordial link with the carbonaceous asteroids, the same bodies that scattered in to become the C-types in the asteroid belt.
  69. Schwamb, M., Fraser, W., Bannister, M., et al., (including Thirouin, A.), 2019, EPSC, 2019, EPSC-DPS2019-1271, A Potential New Surface Type in the Kuiper Belt
    Colours of the Outer Solar System Origins Survey (Col-OSSOS) is probing Kuiper belt object (KBO) surface properties via near simultaneous g,r and J photometry from Gemini North with additional u-band imaging from CFHT. We will present the latest results from the survey including the surface properties of two outlier objects from the Col-OSSOS color distribution that may represent a new surface type present within the small KBO population.
  70. Sickafoose, A., Bosh, A., Emery, J., et al., 2019, EPSC, 2019, EPSC-DPS2019-1306, Characterization of material around (2060) Chiron from a 2011 stellar occultation
    We present results from a stellar occultation by the centaur Chiron from observations in 2011. This work places a constraint on the size of Chiron's nucleus and expands on previous work by analyzing the surrounding material in detail. We find (i) two distinct, thin features that are symmetric around the nucleus and 300 km away; (ii) multiple asymmetric arcs or less-optically-thick material between 200-450 km; and (iii) what is likely a diffuse shell of material extending from 900-1500 km. These results are particularly interesting in the context of the ring system that was discovered around the similarly-sized centaur Chariklo.
  71. Young, L., Porter, S., Keeny, B., et al., (including Thirouin, A., Wasserman, L.), 2019, EPSC, 2019, EPSC-DPS2019-1321, The Gaia-based prediction of the 2019 May 1 occultation of elongated KBO (33128) 1998 BU48
    Gaia should enable the Golden Age of stellar occultations. We planned for an occultation by elongated KBO 1998 BU48, with no positive reported events yet. We will study this example to improve future Gaia-enabled occultations.
  72. Marciniak, A., Oszkiewicz, D., Troianskyi, V., et al., (including Skiff, B., Moskowitz, N.), 2019, EPSC, 2019, EPSC-DPS2019-1379, Investigating V-type asteroids outside Vesta family
    We are conducting a photometric, spectroscopic, and dynamical study of V-type asteroids outside the Vesta family in the inner main belt. The aim is to find traces of once existing differentiated planetesimals other than Vesta, to provide the missing observational evidence for theories predicting an abundance of such planetesimals in the early solar system.
  73. McKinnon, W., Keane, J., Nesvorny, D., et al., (including Grundy, W.), 2019, EPSC, 2019, EPSC-DPS2019-1387, On the Origin of the Remarkable Contact Binary (486958) 2014 MU69 ("Ultima Thule")
    We discuss the remarkable world 2014 MU69, or "Ultima Thule," as revealed by the recent New Horizons flyby. This body reveals hitherto unimagined details of how the building blocks of planets -planetesimals -were actually assembled.
  74. Jehin, E., Moreno, F., Ferrais, M., et al., (including Devogele, M.), 2019, EPSC, 2019, EPSC-DPS2019-1826, A photometric and spectroscopic study of the multi-tailed asteroid (6478) Gault
    In this presentation, we describe several months of monitoring of Gault since January 2019 using various telescopes and instrumentation. The goal is to characterize and to model the asteroids and the tails to impose constraints on the physical properties of the ejected dust, and to shed light on the activity timeline and the causes for the ejection events.
  75. Trujillo, C., Trilling, D., Gerdes, D., et al., (including Mommert, M.), 2019, EPSC, 2019, EPSC-DPS2019-2070, Deep Ecliptic Exploration Project (DEEP) Observing Strategy
    We present the Deep Ecliptic Exploration Project (DEEP) survey strategy including observing cadence for orbit determination, exposure times, field pointings and filter choices. The overall goal of the survey is to discover and characterize the orbits of several thou- sand Trans-Neptunian Objects (TNOs) using the Dark Energy Camera (DECam) on the Cerro Tololo Inter- American Observatory Blanco 4 meter telescope. When complete, DEEP will be the largest survey of the outer solar sys- tem ever undertaken in terms of object numbers and will also be among the deepest.
  76. Levesque, E., Prato, L., Sneden, C., et al., 2019, BAAS, 51, 26, Key Challenges for AAS Journals in the Next Decade
    The AAS Journals are a vital asset to astronomy, but the page charge model for funding their publication could prove challenging in the open access (OA) era. Discussing alternative models for funding publishing costs must be part of Astro2020. We recommend that the NAS form a task force to address the concerns highlighted in this white paper.
  77. Hall, J., Allen, L., Arion, D., et al., 2019, BAAS, 51, 97, Light Pollution, Radio Interference, and Space Debris: Threats and Opportunities in the 2020s
    In this white paper, we will outline threats to astronomy in the areas of light pollution, radio interference, and space debris, and we will specify key principles and policy points that the AAS and other advocates can use in mitigating these threats.
  78. van Belle, G., Armstrong, J., Baines, E., et al., (including Llama, J.), 2019, BAAS, 51, 104, The Navy Precision Optical Interferometer
    We outline a plan for NPOI for 2020-2030 that will provide the highest resolution visible-light system on the planet, with multi-km baselines and sub-mas imaging. This capability will resolve the sizes and shapes of stars, resolve AGNs, image protoplanetary disks, and observe the passage of exoplanets across their stellar disks.
  79. Soderblom, D., Wilkes, B., Saha, A., et al., (including Hall, J.), 2019, BAAS, 51, 116, Research scientists in support of facilities and missions: Facility support and research as an interlocked pair
    Scientists who themselves depend on the facilities that they support have a much deeper knowledge of the facilities, leading to better user support, new modes, more efficient telescope use, and overall more and better scientific output. This white paper supports the value of research scientists at facilities and missions.
  80. Monnier, J., Aarnio, A., Absil, O., et al., (including van Belle, G.), 2019, BAAS, 51, 133, Setting the Stage for the Planet Formation Imager
    The Planet Formation Imager (PFI) is a next-generation infrared interferometer designed to image the active phases of planet formation and to take planetary snapshots of young systems. We outline a technology plan to make PFI a reality, identifying a potential breakthrough opportunity for making inexpensive large telescopes available.
  81. Mawet, D., Fitzgerald, M., Konopacky, Q., et al., (including Prato, L.), 2019, BAAS, 51, 134, High-resolution Infrared Spectrograph for Exoplanet Characterization with the Keck and Thirty Meter Telescopes
    HISPEC (High-resolution Infrared Spectrograph for Exoplanet Characterization) is a proposed diffraction-limited spectrograph for the W.M. Keck Observatory, and a pathfinder for the MODHIS facility project (Multi-Object Diffraction-limited High-resolution Infrared Spectrograph) on the Thirty Meter Telescope.
  82. Monnier, J., Aarnio, A., Absil, O., et al., (including van Belle, G.), 2019, BAAS, 51, 153, A Realistic Roadmap to Formation Flying Space Interferometry
    The ultimate astronomical observatory would be a formation flying space interferometer, combining sensitivity and stability with high angular resolution. The smallSat revolution offers a new and maturing prototyping platform for space interferometry and we put forward a realistic plan for achieving first stellar fringes in space by 2030.
  83. Ridgway, S., Armstrong, J., Baines, E., et al., (including van Belle, G.), 2019, BAAS, 51, 157, Revitalizing the Optical/Infrared Interferometry Community in the U.S.
    Long baseline optical/infrared interferometry (LBOI) has produced groundbreaking results in stellar astrophysics and is essential for the future of high-resolution observations. We describe capabilities and recent results, discuss the development of LBOI in the U.S., and make recommendations for the support and growth of U.S. interferometry.
  84. Rinehart, S., Arenberg, J., Baines, E., et al., (including van Belle, G.), 2019, BAAS, 51, 222, A Long-Term Vision for Space-Based Interferometry
    A number of important astrophysical questions require observations with angular resolution beyond the capabilities of either existing or proposed facilities. We discuss some of these key science questions and present a potential path to obtaining high angular resolution through the development of space-based interferometers.
  85. Harrington, J., Gommers, R., Gentemann, C., et al., (including Llama, J., Hamilton, R.), 2019, BAAS, 51, 265, Support the Python Numerical Core
    Open-source software (OSS) promotes reproducibility and efficiency in science. The most popular OSS framework in astrophysics is the Python Numerical Core (PNC), including the NumPy, SciPy, Matplotlib, Pandas, and Scikit-learn packages. With over 5,000,000 users, these projects have grown beyond the volunteer scale and require financial support.
  86. Alexandersen, M., Benecchi, S., Chen, Y., et al., (including Thirouin, A.), 2019, ApJS, 244, 19, OSSOS. XII. Variability Studies of 65 Trans-Neptunian Objects Using the Hyper Suprime-Cam
    We present variability measurements and partial light curves of trans-Neptunian objects (TNOs) from a two-night pilot study using Hyper Suprime-Cam (HSC) on the Subaru Telescope (Maunakea, Hawaii, USA). Subarus large aperture (8 m) and HSCs large field of view (1.77 deg2) allow us to obtain measurements of multiple objects with a range of magnitudes in each telescope pointing. We observed 65 objects with m r = 22.6-25.5 mag in just six pointings, allowing 20-24 visits of each pointing over the two nights. Our sample, all discovered in the recent Outer Solar System Origins Survey (OSSOS), spans absolute magnitudes of H r = 6.2-10.8 mag and thus investigates smaller objects than previous light curve projects have typically studied. Our data supports the existence of a correlation between the light curve amplitude and absolute magnitude seen in other works but does not support a correlation between the amplitude and orbital inclination. Our sample includes a number of objects from different dynamical populations within the trans-Neptunian region, but we do not find any relationship between variability and the dynamical class. We were only able to estimate periods for 12 objects in the sample and found that a longer baseline of observations is required for a reliable period analysis. We find that 31 objects (just under half of our sample) have variability of {{{ }}}mag} greater than 0.4 mag during all of the observations; in smaller 1.25 hr, 1.85 hr, and 2.45 hr windows, the median {{{ }}}mag} is 0.13, 0.16, and 0.19 mag, respectively. The fact that variability on this scale is common for small TNOs has important implications for discovery surveys (such as OSSOS or the Large Synoptic Survey Telescope) and color measurements.

    Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

  87. Santos, F., Chuss, D., Dowell, C., et al., (including Hamilton, R.), 2019, ApJ, 882, 113, The Far-infrared Polarization Spectrum of Ophiuchi A from HAWC+/SOFIA Observations
    We report on polarimetric maps made with HAWC+/SOFIA toward Oph A, the densest portion of the Ophiuchi molecular complex. We employed HAWC+ bands C (89 m) and D (154 m). The slope of the polarization spectrum was investigated by defining the quantity {{ \mathcal R }}{DC}={p}D/{p}C, where p C and p D represent polarization degrees in bands C and D, respectively. We find a clear correlation between {{ \mathcal R }}{DC} and the molecular hydrogen column density across the cloud. A positive slope ({{ \mathcal R }}{DC} > 1) dominates the lower-density and well-illuminated portions of the cloud, which are heated by the high-mass star Oph S1, whereas a transition to a negative slope ({{ \mathcal R }}{DC} < 1) is observed toward the denser and less evenly illuminated cloud core. We interpret the trends as due to a combination of (1) warm grains at the cloud outskirts, which are efficiently aligned by the abundant exposure to radiation from Oph S1, as proposed in the radiative torques theory; and (2) cold grains deep in the cloud core, which are poorly aligned owing to shielding from external radiation. To assess this interpretation, we developed a very simple toy model using a spherically symmetric cloud core based on Herschel data and verified that the predicted variation of {{ \mathcal R }}{DC} is consistent with the observations. This result introduces a new method that can be used to probe the grain alignment efficiency in molecular clouds, based on the analysis of trends in the far-infrared polarization spectrum.
  88. Marsset, M., DeMeo, F., Sonka, A., et al., (including Burt, B.), 2019, ApJL, 882, L2, Active Asteroid (6478) Gault: A Blue Q-type Surface below the Dust?
    We present near-infrared spectroscopy of the sporadically active asteroid (6478) Gault collected on the 3 m NASA/Infrared Telescope Facility observatory in late 2019 March/early April. Long-exposure imaging with the 0.5 m Near Earth Environment Monitoring T05 telescope and previously published data simultaneously monitored the asteroid activity, providing context for our measurements. We confirm that Gault is a silicate-rich (Q- or S-type) object likely linked to the (25) Phocaea collisional family. The asteroid exhibits substantial spectral variability over the 0.75-2.45 m wavelength range, from unusual blue (s = -13.5 1.1% m-1) to typical red (s = +9.1 1.2% m-1) spectral slope, that does not seem to correlate with activity. Spectral comparisons with samples of ordinary chondrite meteorites suggest that the blue color relates to the partial loss of the asteroid dust regolith, exposing a fresh, dust-free material at its surface. The existence of asteroids rotating close to rotational break-up limit and having similar spectral properties as Gault further supports this interpretation. Future spectroscopic observations of Gault, when the tails dissipate, will help further testing of our proposed hypothesis.
  89. Cruikshank, D., Umurhan, O., Beyer, R., et al., (including Grundy, W.), 2019, Icar, 330, 155, Recent cryovolcanism in Virgil Fossae on Pluto
    The Virgil Fossae region on Pluto exhibits three spatially coincident properties that are suggestive of recent cryovolcanic activity over an area approximately 300 by 200 km. Situated in the fossae troughs or channels and in the surrounding terrain are exposures of H2O ice in which there is entrained opaque red-colored matter of unknown composition. The H2O ice is also seen to carry spectral signatures at 1.65 and 2.2 m of NH3 in some form, possibly as a hydrate, an ammoniated salt, or some other compound. Model calculations of NH3 destruction in H2O ice by galactic cosmic rays suggest that the maximum lifetime of NH3 in the uppermost meter of the exposed surface is 109 years, while considerations of Lyman- ultraviolet and solar wind charged particles suggest shorter timescales by a factor of 10 or 10000. Thus, 109 y is taken as an upper limit to the age of the emplacement event, and it could be substantially younger.

    The red colorant in the ammoniated H2O in Virgil Fossae and surroundings may be a macromolecular organic material (tholin) thought to give color to much of Pluto's surface, but probably different in composition and age. Owing to the limited spectral range of the New Horizons imaging spectrometer and the signal precision of the data, apart from the H2O and NH3 signatures there are no direct spectroscopic clues to the chemistry of the strongly colored deposit on Pluto. We suggest that the colored material was a component of the fluid reservoir from which the material now on the surface in this region was erupted. Although other compositions are possible, if it is indeed a complex organic material it may incorporate organics inherited from the solar nebula, further processed in a warm aqueous environment inside Pluto.

    A planet-scale stress pattern in Pluto's lithosphere induced by true polar wander, freezing of a putative interior ocean, and surface loading has caused fracturing in a broad arc west of Sputnik Planitia, consistent with the structure of Virgil Fossae and similar extensional features. This faulting may have facilitated the ascent of fluid in subsurface reservoirs to reach the surface as flows and as fountains of cryoclastic materials, consistent with the appearance of colored, ammoniated H2O ice deposits in and around Virgil Fossae. Models of a cryoflow emerging from sources in Virgil Fossae indicate that the lateral extent of the flow can be several km (Umurhan et al., 2019). The deposit over the full length (>200 km) of the main trough in the Virgil Fossae complex and extending through the north rim of Elliot crater and varying in elevation over a range of 2.5 km, suggests that it debouched from multiple sources, probably along the length of the strike direction of the normal faults defining the graben. The source or sources of the ammoniated H2O are one or more subsurface reservoirs that may or may not connect to the global ocean postulated for Pluto's interior. Alternatives to cryovolcanism in producing the observed characteristics of the region around Virgil Fossae are explored in the discussion section of the paper.

  90. Bertrand, T., Forget, F., Umurhan, O., et al., (including Grundy, W.), 2019, Icar, 329, 148, The CH4 cycles on Pluto over seasonal and astronomical timescales
    Pluto's surface is covered in numerous CH4 ice deposits, that vary in texture and brightness, as revealed by the New Horizons spacecraft as it flew by Pluto in July 2015. These observations suggest that CH4 on Pluto has a complex history, involving reservoirs of different composition, thickness and stability controlled by volatile processes occurring on different timescales. In order to interpret these observations, we use a Pluto volatile transport model able to simulate the cycles of N2 and CH4 ices over millions of years. By assuming fixed solid mixing ratios, we explore how changes in surface albedos, emissivities and thermal inertias impact volatile transport. This work is therefore a direct and natural continuation of the work by Bertrand et al. (2018), which only explored the N2 cycles. Results show that bright CH4 deposits can create cold traps for N2 ice outside Sputnik Planitia, leading to a strong coupling between the N2 and CH4 cycles. Depending on the assumed albedo for CH4 ice, the model predicts CH4 ice accumulation (1) at the same equatorial latitudes where the Bladed Terrain Deposits are observed, supporting the idea that these CH4-rich deposits are massive and perennial, or (2) at mid-latitudes (25- 70), forming a thick mantle which is consistent with New Horizons observations. In our simulations, both CH4 ice reservoirs are not in an equilibrium state and either one can dominate the other over long timescales, depending on the assumptions made for the CH4 albedo. This suggests that long-term volatile transport exists between the observed reservoirs. The model also reproduces the formation of N2 deposits at mid-latitudes and in the equatorial depressions surrounding the Bladed Terrain Deposits, as observed by New Horizons. At the poles, only seasonal CH4 and N2 deposits are obtained in Pluto's current orbital configuration. Finally, we show that Pluto's atmosphere always contained, over the last astronomical cycles, enough gaseous CH4 to absorb most of the incoming Lyman- flux.
  91. Neugent, K., Massey, P., 2019, Galax, 7, 74, The WolfRayet Content of the Galaxies of the Local Group and Beyond
    WolfRayet stars (WRs) represent the end of a massive star's life as it is about to turn into a supernova. Obtaining complete samples of such stars across a large range of metallicities poses observational challenges, but presents us with an exacting way to test current stellar evolutionary theories. A technique we have developed and refined involves interference filter imaging combined with image subtraction and crowded-field photometry. This helps us address one of the most controversial topics in current massive star research: the relative importance of binarity in the evolution of massive stars and formation of WRs. Here, we discuss the current state of the field, including how the observed WR populations match with the predictions of both single and binary star evolutionary models. We end with what we believe are the most important next steps in WR research.
  92. Clark, C., van Belle, G., Horch, E., et al., (including von Braun, K.), 2019, ESS, 51, 316.03, Understanding the Multiplicity of TESS Exoplanet Host Candidates
    While at first glance multi-star systems seem quite extreme, they are in fact the most common type of star system in our galaxy, throughout the stellar mass distribution. In particular, 40 to 50% of exoplanet host stars reside within multiple star systems. Given the degree to which initially undetected multiplicity has skewed Kepler results, high-resolution imaging of our nearby low-mass neighbors is necessary for both accurate characterization of transiting exoplanets, as well as a better understanding of stellar astrophysics. To address this frequent gap in our knowledge of exoplanet hosts, we will utilize speckle interferometry to directly image TESS exoplanet host candidates to complete our knowledge of individual star multiplicity. Our investigation will expand upon the speckle observations taken as a part of the POKEMON speckle survey of nearby M-dwarfs to better constrain the multiplicity of low-mass TESS exoplanet host candidates, and to constrain M-dwarf multiplicity by subtype across the entire M-dwarf sequence.
  93. Cauley, P., Shkolnik, E., Llama, J., et al., 2019, ESS, 51, 319.09, Magnetic fields of hot Jupiters calculated from star-planet interactions
    Planetary magnetic fields have a critical impact on atmospheric physics, damping winds on hot, short-period planets and potentially creating the necessary conditions for habitability on temperate terrestrial worlds by deflecting stellar wind particles. Despite their importance, exoplanet magnetic field detections remain elusive. For the first time, we report the derivation of the magnetic fields of a sample of hot Jupiters using flux-calibrated signals of magnetic star-planet interactions (SPI). We find that the surface magnetic field values for the hot Jupiters in our sample range from 20 G to 120 G, 10 - 50 times larger than the values predicted by pure dynamo theories for planets with rotation periods of 2 to 4 days. Such large field strengths should have severe consequences for velocity flows in the planets' atmospheres and exhibit peak frequencies of electron-cyclotron emission in the range of facilities such as LOFAR.
  94. Llama, J., Johns-Krull, C., Prato, L., et al., (including Nofi, L., Biddle, L.), 2019, ESS, 51, 322.02, Formation and atmospheric constraints of the youngest hot Jupiter.
    The last three years have ushered in the era of young exoplanets. Despite young stars exhibiting extreme levels of variability, a handful of newly formed exoplanets have been detected through transits and radial velocity. We will present the latest results from our young planet survey. For the first time, using high-resolution infrared spectra, we have a direct detection of CO in the atmosphere of the youngest exoplanet CI Tau b, confirming the planet, and providing evidence for a hot start mechanism. Our discovery shows that hot Jupiters either form incredibly close to their parent star, or, that migration occurs within the first 2 Myr.
  95. van Belle, G., Clark, C., Horch, E., et al., 2019, ESS, 51, 330.17, Exoplanet Host Star Characterization with QWSSI
    QWSSI, the Quad-camera Wavefront-Sensing Speckle Imager, is a next-generation speckle imager that is being developed for Lowell Observatory's 4.3-meter Discovery Channel Telescopes. The principle behind QWSSI is to extend the capabilities of the speckle camera currently resident at Lowell, the Differential Speckle Survey Instrument (DSSI), in two ways. First, while DSSI currently observes in two visible channels, QWSSI will simultaneously observe in six narrow-band channels: four in the visible (0.5-0.9um), and one each in J- and H-band (1.2 and 1.6um). Second, the visible light unused for speckle imaging is carefully preserved and feeds a wavefront sensor (WFS), which is also run simultaneously with the speckle imaging. Simulations by Lobb (2016) indicate WFS data will provide significant gains in exploring stellar multiplicity, with marked improvements in primary-secondary contrast ratios and inner working angle (Horch et al. 2018). QWSSI will also be mountable on one of the three 1-meter telescopes being installed on the NPOI Array for engineering tests and preliminary science observations. QWSSI will expand on the already considerable exoplanetary work of the speckle imagers DSSI, NESSI (@ WIYN), Alopeke (Gemini-N), and Zorro (Gemini-S), improving the discovery space for existing targets, as well opening up new regions of that discovery space with its NIR channels.
  96. Mommert, M., Kelley, M., de Val-Borro, M., et al., (including Grundy, W., Moskovitz, N.), 2019, JOSS, 4, 1426, sbpy: A Python module for small-body planetary astronomy
    No abstract found.
  97. Hutter, D., Tycner, C., Zavala, R., et al., (including Sanborn, J.), 2019, ApJS, 243, 32, Surveying the Bright Stars by Optical Interferometry. II. A Volume-limited Multiplicity Survey of Main-sequence F Stars
    We present the results of a multiplicity survey for a volume-limited sample of 29 main-sequence F0-G0 stars within 17 pc conducted with the Navy Precision Optical Interferometer (NPOI). Four companions were detected in previously known binary systems. The results for these stars show good agreement with previously published orbits. For one of these sources, Peg, the modeling of our data, which includes closure phase information, confirms the quadrant of the orbit. No new companions were detected in the sample (within separations of 3-860 mas and contrasts down to 3.5 mag at 700 nm). Combined with an extensive literature search, we provide a detailed listing of companions known around each star in the sample from prior spectroscopic and imaging/speckle observations, and we discuss the multiplicity frequency in the sample. We also discuss the prospects for future stellar multiplicity studies with the NPOI.
  98. Sanchez, J., Reddy, V., Thirouin, A., et al., 2019, ApJL, 881, L6, Physical Characterization of Active Asteroid (6478) Gault
    Main belt asteroid (6478) Gault has been dynamically linked with two overlapping asteroid families: Phocaea, dominated by S-type asteroids, and Tamara, dominated by low-albedo C-types. This object has recently become an interesting case for study after images obtained in late 2018 revealed that it was active and displaying a comet-like tail. Previous authors have proposed that the most likely scenarios to explain the observed activity on Gault were rotational excitation or merger of near-contact binaries. Here we use new photometric and spectroscopic data of Gault to determine its physical and compositional properties. Lightcurves derived from the photometric data showed little variation over three nights of observations, which prevented us from determining the rotation period of the asteroid. Using WISE observations of Gault and the near-Earth Asteroid Thermal Model (NEATM) we determined that this asteroid has a diameter <6 km. Near-infrared spectroscopic data obtained with the Infrared Telescope Facility showed a spectrum similar to that of S-complex asteroids, and a surface composition consistent with H chondrite meteorites. These results favor a compositional affinity between Gault and asteroid (25) Phocaea, and rules out a compositional link with the Tamara family. From the spectroscopic data we found no evidence of fresh material that could have been exposed during the outburst episodes.
  99. Healy, B., Han, E., Muirhead, P., et al., (including Skiff, B.), 2019, AJ, 158, 89, Magnetic Inflation and Stellar Mass. III. Revised Parameters for the Component Stars of NSVS 07394765
    We perform a new analysis of the M-dwarf-M-dwarf eclipsing binary system NSVS 07394765 in order to investigate the reported hyper-inflated radius of one of the component stars. Our analysis is based on archival photometry from the Wide Angle Search for Planets, new photometry from the 32 cm Command Module Observatory telescope in Arizona and the 70 cm telescope at Thacher Observatory in California, and new high-resolution infrared spectra obtained with the Immersion Grating Infrared Spectrograph on the Discovery Channel Telescope. The masses and radii we measure for each component star disagree with previously reported measurements. We show that both stars are early M-type main-sequence stars without evidence for youth or hyper-inflation ({M}1={0.661}-0.036+0.008 {M} , {M}2={0.608}-0.028+0.003 {M} , {R}1={0.599}-0.019+0.032 {R} , {R}2={0.625}-0.027+0.012 {R} ), and we update the orbital period and eclipse ephemerides for the system. We suggest that the likely cause of the initial hyper-inflated result is the use of moderate-resolution spectroscopy for precise radial velocity measurements.
  100. Gustafsson, A., Trilling, D., Mommert, M., et al., 2019, AJ, 158, 67, Spitzer Albedos of Near-Earth Objects
    Thermal infrared observations are the most effective way to measure asteroid diameter and albedo for a large number of near-Earth objects (NEOs). Major surveys like NEOWISE, NEOSurvey, ExploreNEOs, and NEOLegacy find a small fraction of high albedo objects that do not have clear analogs in the current meteorite population. About 8% of Spitzer-observed NEOs have nominal albedo solutions greater than 0.5. This may be a result of light-curve variability leading to an incorrect estimate of diameter or inaccurate absolute visual magnitudes. For a sample of 23 high-albedo NEOs we do not find that their shapes are significantly different from the McNeill et al. NEO shape distribution. We performed a Monte Carlo analysis on 1505 NEOs observed by Spitzer, sampling the visible and thermal fluxes of all targets to determine the likelihood of obtaining a high albedo erroneously. Implementing the McNeill shape distribution for NEOs, we provide an upper limit on the geometric albedo of 0.5 0.1 for the near-Earth population.
  101. Thirouin, A., Sheppard, S., 2019, AJ, 158, 53, Colors of Trans-Neptunian Contact Binaries
    The gri colors of seven likely and potential contact binaries in the Kuiper Belt were acquired with the Magellan-Baade telescope and combined with colors from the literature to understand contact binary surfaces. The likely and potential contact binaries discovered in the dynamically cold classical population display very red/ultra-red colors. Such colors are common in this sub-population and imply that the cold classical contact binaries were formed in situ. The likely contact binaries found in several mean motion resonances with Neptune have colors from moderately to ultra-red, suggesting different formation regions. Among the nine contact binaries discovered in resonances, five have very red/ultra-red colors and four have moderately red surfaces. Based on the very red/ultra-red colors and low to moderate inclinations of the contact binaries in resonances, these contact binaries are possibly escaped dynamically cold classicals that are now trapped in resonances. Moderately red surfaces are common in diverse sub-populations of the Kuiper Belt, thus pinpointing their origin is difficult though they are most likely captured objects that formed in the giant planet area. Finally, for the contact binary population we report an anti-correlation between inclination and g-r, as noticed in the rest of this belt. We also find hints of trends between eccentricity, perihelion distance, rotational period, and g-r, but as we are still dealing with a limited sample, additional data are required to confirm them.
  102. Cauley, P., Shkolnik, E., Llama, J., et al., 2019, NatAs, 3, 1128, Magnetic field strengths of hot Jupiters from signals of star-planet interactions
    Evidence of star-planet interactions in the form of planet-modulated chromospheric emission has been noted for a number of hot Jupiters. Magnetic star-planet interactions involve the release of energy stored in the stellar and planetary magnetic fields. These signals thus offer indirect detections of exoplanetary magnetic fields. Here, we report the derivation of the magnetic field strengths of four hot Jupiter systems, using the power observed in calcium uc(ii) K emission modulated by magnetic star-planet interactions. By approximating the fractional energy released in the calcium uc(ii) K line, we find that the surface magnetic field values for the hot Jupiters in our sample range from 20 G to 120 G, around 10-100 times larger than the values predicted by dynamo scaling laws for planets with rotation periods of around 2-4 days. However, these values are in agreement with scaling laws relating the magnetic field strength to the internal heat flux in giant planets. Large planetary magnetic field strengths may produce observable electron cyclotron maser radio emission by preventing the maser from being quenched by the planet's ionosphere. Intensive radio monitoring of hot Jupiter systems will help to confirm these field values and inform the generation mechanism of magnetic fields in this important class of exoplanets.
  103. Garofali, K., Levesque, E., Massey, P., et al., 2019, ApJ, 880, 8, The First Candidate Colliding-wind Binary in M33
    We present the detection of the first candidate colliding-wind binary (CWB) in M33, located in the giant H II region NGC 604. The source was first identified in archival Chandra imaging as a relatively soft X-ray point source, with the likely primary star determined from precise astrometric alignment between archival Hubble Space Telescope and Chandra imaging. The candidate primary star in the CWB is classified for the first time in this work as a carbon-rich Wolf-Rayet star with a likely O-star companion based on spectroscopy obtained from Gemini-North. We model the X-ray spectrum using Chandra and XMM-Newton observations, and find the CWB to be well fit as a 1 keV thermal plasma with a median unabsorbed luminosity in the 0.5-2.0 keV band of L X 3 1035 erg s-1, making this source among the brightest of CWBs observed to date. We present a long-term light curve for the candidate CWB from archival Chandra and XMM-Newton observations, and discuss the constraints placed on the binary by this light curve, as well as the X-ray luminosity at maximum. Finally, we compare this candidate CWB in M33 to other well-studied, bright CWBs in the Galaxy and Magellanic Clouds, such as Car.
  104. Schwamb, M., Fraser, W., Bannister, M., et al., (including Thirouin, A.), 2019, ApJS, 243, 12, Col-OSSOS: The Colors of the Outer Solar System Origins Survey
    The Colours of the Outer Solar System Origins Survey is acquiring near-simultaneous g, r, and J photometry of unprecedented precision with the Gemini North Telescope, targeting nearly 100 trans-Neptunian objects (TNOs) brighter than m r = 23.6 mag discovered in the Outer Solar System Origins Survey. Combining the optical and near-infrared photometry with the well-characterized detection efficiency of the Colours of the Outer Solar System Origins Survey target sample will provide the first flux-limited compositional dynamical map of the outer solar system. In this paper, we describe our observing strategy and detail the data reduction processes we employ, including techniques to mitigate the impact of rotational variability. We present optical and near-infrared colors for 35 TNOs. We find two taxonomic groups for the dynamically excited TNOs, the neutral and red classes, which divide at g - r 0.75. Based on simple albedo and orbital distribution assumptions, we find that the neutral class outnumbers the red class, with a ratio of 4:1 and potentially as high as 11:1. Including in our analysis constraints from the cold classical objects, which are known to exhibit unique albedos and r - z colors, we find that within our measurement uncertainty our observations are consistent with the primordial solar system protoplanetesimal disk being neutral class dominated, with two major compositional divisions in grJ color space.
  105. Cruikshank, D., Materese, C., Pendleton, Y., et al., (including Grundy, W.), 2019, AsBio, 19, 831, Prebiotic Chemistry of Pluto
    We present the case for the presence of complex organic molecules, such as amino acids and nucleobases, formed by abiotic processes on the surface and in near-subsurface regions of Pluto. Pluto's surface is tinted with a range of non-ice substances with colors ranging from light yellow to red to dark brown; the colors match those of laboratory organic residues called tholins. Tholins are broadly characterized as complex, macromolecular organic solids consisting of a network of aromatic structures connected by aliphatic bridging units (e.g., Imanaka et al., ). The red material associated with the H2O ice may contain nucleobases resulting from energetic processing on Pluto's surface or in the interior. Some other Kuiper Belt objects also exhibit red colors similar to those found on Pluto and may therefore carry similar inventories of complex organic materials. The widespread and ubiquitous nature of similarly complex organic materials observed in a variety of astronomical settings drives the need for additional laboratory and modeling efforts to explain the origin and evolution of organic molecules. Pluto observations reveal complex organics on a small body that remains close to its place of origin in the outermost regions of the Solar System.
  106. Tegler, S., Stufflebeam, T., Grundy, W., et al., (including Hanley, J., Llama, J.), 2019, AJ, 158, 17, A New Two-molecule Combination Band as a Diagnostic of Carbon Monoxide Diluted in Nitrogen Ice on Triton
    A combination band due to a mechanism whereby a photon excites two or more vibrational modes (e.g., a bend and a stretch) of an individual molecule is commonly seen in laboratory and astronomical spectroscopy. Here, we present evidence of a much less commonly seen combination bandone where a photon simultaneously excites two adjacent molecules in an ice. In particular, we present near-infrared spectra of laboratory CO/N2 ice samples where we identify a band at 4467.5 cm-1 (2.239 m) that results from single photons exciting adjacent pairs of CO and N2 molecules. We also present a near-infrared spectrum of Neptunes largest satellite Triton taken with the Gemini-South 8.1 m telescope and the Immersion Grating Infrared Spectrograph that shows this 4467.5 cm-1 (2.239 m) CO-N2 combination band. The existence of the band in a spectrum of Triton indicates that CO and N2 molecules are intimately mixed in the ice rather than existing as separate regions of pure CO and pure N2 deposits. Our finding is important because CO and N2 are the most volatile species on Triton and so dominate seasonal volatile transport across its surface. Our result will place constraints on the interaction between the surface and atmosphere of Triton.
  107. Hunter, D., Laufman, L., Oh, S., et al., (including Levine, S.), 2019, AJ, 158, 23, Gas Engaged in Noncircular Motions in LITTLE THINGS Dwarf Irregular Galaxies
    We have examined gas engaged in noncircular motions in 22 of the nearby LITTLE THINGS dwarf irregular galaxies. The H I data cubes have been deconvolved into kinematic componentsbulk rotation and noncircular motionsto produce maps of integrated gas, velocity field, and velocity dispersion in the different components. We found significant regions of gas engaged in noncircular motions in half of the galaxies, involving 1%-20% of the total H I mass of the galaxy. In one galaxy we found a pattern in the velocity field that is characteristic of streaming motions around the stellar bar potential and star formation at the end of bar. Two galaxies have large-scale filamentary structures found in their outer disks, and these filaments could be transient instabilities in the gas. We found no spatial correlation between noncircular motion gas and enhanced star formation. We found noncircular motion gas in only one galaxy associated with higher H I velocity dispersion.
  108. Kostov, V., Schlieder, J., Barclay, T., et al., (including van Belle, G.), 2019, AJ, 158, 32, The L 98-59 System: Three Transiting, Terrestrial-size Planets Orbiting a Nearby M Dwarf
    We report the Transiting Exoplanet Survey Satellite (TESS) discovery of three terrestrial-size planets transiting L 98-59 (TOI-175, TIC 307210830)a bright M dwarf at a distance of 10.6 pc. Using the Gaia-measured distance and broadband photometry, we find that the host star is an M3 dwarf. Combined with the TESS transits from three sectors, the corresponding stellar parameters yield planet radii ranging from 0.8 R to 1.6 R . All three planets have short orbital periods, ranging from 2.25 to 7.45 days with the outer pair just wide of a 2:1 period resonance. Diagnostic tests produced by the TESS Data Validation Report and the vetting package DAVE rule out common false-positive sources. These analyses, along with dedicated follow-up and the multiplicity of the system, lend confidence that the observed signals are caused by planets transiting L 98-59 and are not associated with other sources in the field. The L 98-59 system is interesting for a number of reasons: the host star is bright (V = 11.7 mag, K = 7.1 mag) and the planets are prime targets for further follow-up observations including precision radial-velocity mass measurements and future transit spectroscopy with the James Webb Space Telescope; the near-resonant configuration makes the system a laboratory to study planetary system dynamical evolution; and three planets of relatively similar size in the same system present an opportunity to study terrestrial planets where other variables (age, metallicity, etc.) can be held constant. L 98-59 will be observed in four more TESS sectors, which will provide a wealth of information on the three currently known planets and have the potential to reveal additional planets in the system.
  109. Reddy, V., Kelley, M., Farnocchia, D., et al., (including Mommert, M., Moskovitz, N.), 2019, Icar, 326, 133, Near-Earth asteroid 2012 TC4 observing campaign: Results from a global planetary defense exercise
    Impacts due to near-Earth objects (NEOs) are responsible for causing some of the great mass extinctions on Earth. While nearly all NEOs of diameter > 1 km, capable of causing a global climatic disaster, have been discovered and have negligible chance of impacting in the near future, we are far from completion in our effort to detect and characterize smaller objects. In an effort to test our preparedness to respond to a potential NEO impact threat, we conducted a community-led global planetary defense exercise with support from the NASA Planetary Defense Coordination Office. The target of our exercise was 2012 TC4, the 10 m diameter asteroid that made a close pass by the Earth on 2017 October 12 at a distance of about 50,000 km. The goal of the TC4 observing campaign was to recover, track, and characterize 2012 TC4 as a hypothetical impactor in order to exercise the global planetary defense system involving observations, modeling, prediction, and communication. We made three attempts with the Very Large Telescope (VLT) on 2017 July 27, 31 and on 2017 August 5 and recovered 2012 TC4 within its ephemeris uncertainty at 2.2 arcmin from the nominal prediction. At visual magnitude V = 27, the recovery of 2012 TC4 is the faintest NEA detection thus far. If an impact during the 2017 close approach had been possible based on the 2012 astrometric data, these recovery observations would have been sufficient to confirm or rule out the impact. The first automatic detection by a survey (Pan-STARRS1) was on September 25, which is the earliest that 2012 TC4 would have been discovered in survey mode, if it had not been discovered in 2012. We characterized 2012 TC4 using photometry, spectroscopy and radar techniques. Based on photometric observations, we determined a rotation period of 12.2 min with an amplitude of 0.9 magnitudes. An additional lower amplitude period was detected, indicating that 2012 TC4 was in a state of non-principal axis rotation. The combined visible and near-infrared spectrum puts it in the taxonomic X-class. Radar images at 1.875 m resolution placed only a few range pixels on the asteroid, reveal an angular, asymmetric, and elongated shape, and establish that 2012 TC4 is less than 20 m on its long axis. We estimate a circular polarization ratio of 0.57 + -0.08 that is relatively high among NEAs observed to date by radar. We also performed a probabilistic impact risk assessment exercise for hypothetical impactors based on the 2012 TC4 observing campaign. This exercise was performed as part of ongoing efforts to advance effective impact risk models and assessment processes for planetary defense. The 2012 TC4 close approach provided a valuable opportunity to test the application of these methods using realistically evolving observational data to define the modeling inputs. To this end, risk assessments were calculated at several epochs before and during the close approach, incorporating new information about 2012 TC4 as it became available. Two size ranges were assessed-one smaller size range (H = 26.7) similar to the actual 2012 TC4, and one larger size range (H = 21.9) to produce a greater-damage scenario for risk assessment. Across the epochs, we found that only irons caused significant damage for smaller size. For the larger size case, however, hydrous stones caused the greatest damage, anhydrous stones caused the least damage, and irons caused moderate damage. We note that the extent of damage depends on composition in different size regimes and, after astrometry, size is the most important physical property to determine for an incoming object.
  110. Loyd, R., France, K., Jin, M., et al., (including Llama, J.), 2019, hst, 15803, Constraining CME Masses on the Active K Star and Planet Host Epsilon Eridani
    If the frequent, energetic flares of active stars are each accompanied by a coronal mass ejection (CME), the effect on stellar and planetary evolution could be strong. Every CME event carries mass and angular momentum away from the star, and each has the potential to impact and strip atmospheric gas from orbiting planets. Developing observational constraints on stellar CMEs is essential to assessing their true impact on stellar and planetary evolution. Such constraints are possible via the unique FUV capabilities of HST. In the FUV, photometry of the coronal Fe XXI 1354 A emission line can constrain the mass of CMEs that accompany flares through an effect known as coronal dimming. Coronal dimming is a direct result of the ejection of emitting coronal material, which leaves behind a dark void reliably detected in Sun-as-a-star observations as a drop in the disk-integrated emission of coronal lines. We propose a coronal dimming analysis of 10 h of high S/N archival COS G130M data of the K dwarf planet host Epsilon Eridani (Eps Eri), containing several flares to constrain the masses of associated CMEs. We will accompany this analysis with detailed MHD modeling of Eps Eri's corona to simulate the dimming in Fe XXI 1354 A emission following CMEs. This analysis will lay fundamental groundwork for future dedicated HST CME observations, develop theoretical tools for interpreting dimming signals through MHD analysis, and test whether CMEs could be a dominant contributor to Eps Eri's high observed mass loss rate.
  111. Massey, P., Neugent, K., Levesque, E., 2019, AJ, 157, 227, The Discovery of Quasi-stellar Objects behind M31 and M33
    We report the discovery of 11 newly found quasars behind the stellar disks of the spiral galaxies M31 and M33 in the fields covered by the Local Group Galaxy Survey. Their redshifts range from 0.37 to 2.15. Most are X-ray, ultraviolet, and infrared sources. We also report the discovery of five normal background galaxies. Most of these objects were observed owing to their anomalous colors, as part of a program (reported elsewhere) to confirm spectroscopically candidate red supergiant plus B-star binaries; others were discovered as part of our identification of early-type massive stars based upon their optical colors. There are 15 previously known quasars in the same fields, for a grand total of 26, 15 behind M31 and 11 behind M33. Of these, only eight were discovered as part of surveys for quasars; the rest were found accidentally. The quasars are well distributed in the M31 and M33 fields, except for the inner regions, and have the potential for being good probes of the interstellar medium in these stellar disks, as well as serving as zero-point calibrators for Gaia parallaxes.
  112. Thirouin, A., Sheppard, S., 2019, AJ, 157, 228, Light Curves and Rotational Properties of the Pristine Cold Classical Kuiper Belt Objects
    We present a survey of the rotational and physical properties of the dynamically low inclination Cold Classical (CC) trans-Neptunian objects (TNOs). The CCs are primordial planetesimals and contain information about our solar system and planet formation over the first 100 million years after the Suns formation. We obtained partial/complete light curves for 42 CCs. We use statistical tests to derive general properties about the shape and rotational frequency distributions of the CCs and infer that they have slower rotations and are more elongated/deformed than the other TNOs. On the basis of the full light curves, the mean rotational period of the CCs is 9.48 1.53 hr compared to 8.45 0.58 hr for the rest of the TNOs. About 65% of the TNOs have a light-curve amplitude below 0.2 mag compared to the 36% of CCs with small amplitude. We present the full light curve of one likely contact binary, 2004 VC131, with a potential density of 1 g cm-3 for a mass ratio of 0.4. We have hints that 2004 MU8 and 2004 VU75 are perhaps potential contact binaries, on the basis of their sparse light curves, but more data are needed to confirm this finding. Assuming equal-sized binaries, we find that 10%-25% of the CCs could be contact binaries, suggesting a deficit of contact binaries in this population compared to previous estimates and to the (40%-50%) possible contact binaries in the Plutino population. These estimates are lower limits and may increase if nonequal-sized contact binaries are considered. Finally, we put in context the results of the New Horizons flyby of 2014 MU69.
  113. Hunter, D., Elmegreen, B., Berger, C., 2019, AJ, 157, 241, H I Clouds in LITTLE THINGS Dwarf Irregular Galaxies
    We identify 814 discrete H I clouds in 40 dwarf irregular galaxies from the LITTLE THINGS survey using an automated cloud-finding algorithm. The cloud masses range from 103 to 107 M , have a surface density averaged over all of the clouds of 9.65 M pc-2, and constitute 2%-53% of the total H I mass of the host galaxy. For individual clouds, the mass including He varies with cloud radius as {log} {M}gas}=(2.11+/- 0.04) {log} {R}cl} +(0.78+/- 0.08) and the internal velocity dispersion varies as {log} {V}disp}=0.5 {log} {R}cl}-0.57+/- 0.21. The H I clouds tend to be in the outer regions of the galaxies, with 72% of the galaxies having more than 70% of their clouds outside one disk scale length and 32% of the galaxies having more than 50% of their clouds outside the radius encircling the H II emission. Thirty-six percent of the clouds are essentially non-self-gravitating from H I alone, with a virial parameter that exceeds vir 10, and 5% have vir 2. We estimate the missing molecular mass, based on the total star formation rate and a typical molecular consumption time of 2 Gyr, as observed in CO-rich galaxies. The resulting molecular fraction has a value averaged over the galaxies of 0.23 and correlates with both the surface density of star formation and the fraction of H I clouds in the outer regions. We conclude that a significant fraction of the inner parts of these dwarf galaxy disks is in the form of dark molecular gas, and that this fraction could be high enough to make the inner disks mildly gravitationally unstable as a precursor to star formation.
  114. Levine, S., Henden, A., Terrell, D., et al., 2019, JAVSO, 47, 132, Solar System Objects and the AAVSO Photometric All-Sky Survey (APASS) (Abstract)
    (Abstract only) The AAVSO Photometric All-Sky Survey, data release 10 (APASS DR10) can be used for photometric calibration of observations of moving objects. Because APASS provides calibrated photometry over the whole sky, it makes it much simpler to tie together observations of objects, like asteroids and comets, that move appreciable distances over the time they are observed. Because the photometric standards are in each image, it will also be possible to recover photometry at the few percent level from non-photometric nights. In addition to providing calibration for new observations, the original APASS data comprise over 500,000 images, each 7.8 square degrees in size, taken over the course of more than nine years. We have searched those images for known Solar System bodies, and present the initial results of this search. For many of the objects found, we have simultaneous five color (B,V, g', r', and i') photometry. APASS provides photometric standards in at least five colors over the magnitude range 7 to 17, which makes it a good match for calibration for telescopes ranging from a few inches in size up to several meters.
  115. Flagg, L., Johns-Krull, C., Nofi, L., et al., (including Llama, J., Prato, L.), 2019, ApJL, 878, L37, CO Detected in CI Tau b: Hot Start Implied by Planet Mass and M K
    We acquired high-resolution infrared spectra of CI Tau, the host star of one of the few young planet candidates amenable to direct spectroscopic detection. We confirm the planets existence with a direct detection of CO in the planets atmosphere. We also calculate a mass of 11.6 M J based on the amplitude of its radial velocity variations. We estimate its flux contrast with its host star to get an absolute magnitude estimate for the planet of 8.17 in the K-band. This magnitude implies the planet formed via a hot start formation mechanism. This makes CI Tau b the youngest confirmed exoplanet as well as the first exoplanet around a T Tauri star with a directly determined, model-independent dynamical mass.
  116. Erasmus, N., McNeill, A., Mommert, M., et al., 2019, ApJS, 242, 15, A Taxonomic Study of Asteroid Families from KMTNET-SAAO Multiband Photometry
    We present here multiband photometry for over 2000 Main-Belt asteroids. For each target, we report the probabilistic taxonomy using the measured V - R and V - I colors in combination with a machine-learning-generated decision surface in color-color space. Through this method, we classify >85% of our targets as one the four main Bus-DeMeo complexes: S-, C-, X-, or D-type. Roughly one-third of our targets have a known associated dynamic family, with 69 families represented in our data. Within uncertainties, our results show no discernible difference in taxonomic distribution between family members and non-family members. Nine of the sixty-nine families represented in our observed sample had 20 or more members present, and therefore, we investigate the taxonomy of these families in more detail and find excellent agreement with the literature. Out of these nine well-sampled families, our data show that the Themis, Koronis, Hygiea, Massalia, and Eunomia families display a high degree of taxonomic homogeneity and that the Vesta, Flora, Nysa-Polana, and Eos families show a significant level of mixture in taxonomies. Using the taxonomic purity and the degree of dispersion in observed colors for each of the nine well-sampled collisional families, we also speculate which of these families potentially originated from a differentiated parent body and/or is a family with a possible undetermined nested family. In addition, we obtained sufficient photometric data for 433 of our targets to extract reliable rotation periods and observe no obvious correlation between rotation properties and family membership.
  117. Johns-Krull, C., Flagg, L., Nofi, L., et al., (including Llama, J., Prato, L.), 2019, AAS, 234, s, Direct Detection of CO in CI Tau b: Support for Hot Start Formation
    We analyze high resolution IR spectra of CI Tau, the host star of one of the few young planet candidates amenable to such observations. We confirm the planet's existence with a direct detection of CO in the planet's atmosphere. We determine a mass of 11.6 Mjup based on the amplitude of the planet's radial velocity variations. We estimate the planet's flux contrast with its host star to obtain an absolute magnitude estimate for the planet of 8.17 in the K band. This magnitude implies the planet formed via a "hot start" formation mechanism. This makes CI Tau b the youngest confirmed exoplanet as well as the first exoplanet around a T Tauri star with a directly determined, model-independent, dynamical mass.
  118. Carvalho, A., Johns-Krull, C., Prato, L., 2019, AAS, 234, 201.06, Radial Velocity Monitoring of the Young Star Hubble 4
    We have been spectroscopically monitoring the young star Hubble 4 for approximately 10 years using the 2.7 m Harlan J. Smith telescope at McDonald Observatory. Our goal is to monitor this star's radial velocity (RV) variations, and we have collected over 65 observations of this 2-3 Myr old T Tauri star. In addition, we analyze archival imaging of Hubble 4 obtained with the ACS instrument aboard the Hubble Space Telescope to measure the flux ratio between the members of this binary system. The RV measurements of Hubble 4 clearly reveal the long period ( 9 yr) variations due to the orbit of this binary (semi-major axis of 5.6 AU) as well as much shorter period ( 1.5 d) variations due to stellar rotation. By fitting and removing the variations due to orbital motion, we also find lower bound of 5 yr on the lifetime of star spots on the surface of the star. We discuss the implications of these findings for RV searches aimed at detecting planets around young stars.
  119. Hahne, F., Horch, E., Ciardi, D., et al., (including van Belle, G.), 2019, AAS, 234, 303.01, Fundamental Stellar Parameters and Multiplicity Rates of M-Dwarfs through Optical Speckle and NIR AO Imaging
    We present preliminary fundamental stellar parameters and multiplicity rates of M dwarf stars using a combination of speckle imaging and adaptive optics. Our survey mainly uses the Differential Speckle Survey Instrument (DSSI) at Lowell Observatory's Discovery Channel Telescope (DCT). DSSI observes speckle patterns simultaneously at two separate wavelengths and the data for this project are composed of observations which span from 2016 to 2018. More recently, the speckle data for some of the target stars that have been found to be binary have been supplemented with observations using Adaptive Optics (AO) at Palomar Observatory. The combination of speckle data in the visible and AO data in the near-infrared allows us to make robust determinations of the luminosities and effective temperatures of the components in each case. Using the known Mass-Luminosity Relation, we also estimate the component masses. A discussion of interesting systems will be given.
  120. Kavanagh, R., Vidotto, A., O. Fionnagain, D., et al., (including Llama, J.), 2019, MNRAS, 485, 4529, MOVES - II. Tuning in to the radio environment of HD189733b
    We present stellar wind modelling of the hot Jupiter host HD189733, and predict radio emission from the stellar wind and the planet, the latter arising from the interaction of the stellar wind with the planetary magnetosphere. Our stellar wind models incorporate surface stellar magnetic field maps at the epochs 2013 June/July, 2014 September, and 2015 July as boundary conditions. We find that the mass-loss rate, angular momentum loss rate, and open magnetic flux of HD189733 vary by 9 per cent, 40 per cent, and 19 per cent over these three epochs. Solving the equations of radiative transfer, we find that from 10 MHz-100 GHz the stellar wind emits fluxes in the range of 10-3-5 Jy, and becomes optically thin above 10 GHz. Our planetary radio emission model uses the radiometric Bode's law, and neglects the presence of a planetary atmosphere. For assumed planetary magnetic fields of 1-10 G, we estimate that the planet emits at frequencies of 2-25 MHz, with peak flux densities of 102 mJy. We find that the planet orbits through regions of the stellar wind that are optically thick to the emitted frequency from the planet. As a result, unattenuated planetary radio emission can only propagate out of the system and reach the observer for 67 per cent of the orbit for a 10 G planetary field, corresponding to when the planet is approaching and leaving primary transit. We also find that the plasma frequency of the stellar wind is too high to allow propagation of the planetary radio emission below 21 MHz. This means a planetary field of at least 8 G is required to produce detectable radio emission.
  121. Meza, E., Sicardy, B., Assafin, M., et al., (including Wasserman, L., Devogele, M.), 2019, A&A, 625, A42, Lower atmosphere and pressure evolution on Pluto from ground-based stellar occultations, 1988-2016
    Context. The tenuous nitrogen (N2) atmosphere on Pluto undergoes strong seasonal effects due to high obliquity and orbital eccentricity, and has recently (July 2015) been observed by the New Horizons spacecraft.
    Aims: The main goals of this study are (i) to construct a well calibrated record of the seasonal evolution of surface pressure on Pluto and (ii) to constrain the structure of the lower atmosphere using a central flash observed in 2015.
    Methods: Eleven stellar occultations by Pluto observed between 2002 and 2016 are used to retrieve atmospheric profiles (density, pressure, temperature) between altitude levels of ~5 and ~380 km (i.e. pressures from ~ 10 bar to 10 nbar).
    Results: (i) Pressure has suffered a monotonic increase from 1988 to 2016, that is compared to a seasonal volatile transport model, from which tight constraints on a combination of albedo and emissivity of N2 ice are derived. (ii) A central flash observed on 2015 June 29 is consistent with New Horizons REX profiles, provided that (a) large diurnal temperature variations (not expected by current models) occur over Sputnik Planitia; and/or (b) hazes with tangential optical depth of ~0.3 are present at 4-7 km altitude levels; and/or (c) the nominal REX density values are overestimated by an implausibly large factor of ~20%; and/or (d) higher terrains block part of the flash in the Charon facing hemisphere.
  122. Marciniak, A., Ali-Lagoa, V., Muller, T., et al., (including Skiff, B.), 2019, A&A, 625, A139, Thermal properties of slowly rotating asteroids: results from a targeted survey
    Context. Earlier work suggests that slowly rotating asteroids should have higher thermal inertias than faster rotators because the heat wave penetrates deeper into the subsurface. However, thermal inertias have been determined mainly for fast rotators due to selection effects in the available photometry used to obtain shape models required for thermophysical modelling (TPM).
    Aims: Our aims are to mitigate these selection effects by producing shape models of slow rotators, to scale them and compute their thermal inertia with TPM, and to verify whether thermal inertia increases with the rotation period.
    Methods: To decrease the bias against slow rotators, we conducted a photometric observing campaign of main-belt asteroids with periods longer than 12 h, from multiple stations worldwide, adding in some cases data from WISE and Kepler space telescopes. For spin and shape reconstruction we used the lightcurve inversion method, and to derive thermal inertias we applied a thermophysical model to fit available infrared data from IRAS, AKARI, and WISE.
    Results: We present new models of 11 slow rotators that provide a good fit to the thermal data. In two cases, the TPM analysis showed a clear preference for one of the two possible mirror solutions. We derived the diameters and albedos of our targets in addition to their thermal inertias, which ranged between 3-3+33 and 45-30+60 J m-2 s-1/2 K-1.
    Conclusions: Together with our previous work, we have analysed 16 slow rotators from our dense survey with sizes between 30 and 150 km. The current sample thermal inertias vary widely, which does not confirm the earlier suggestion that slower rotators have higher thermal inertias.

    Full Table A.1 and photometric data from all individual nights 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/625/A139

  123. Carpenter, K., van Belle, G., Brown, A., et al., 2019, BAAS, 51, 56, Stars at High Spatial Resolution
    We summarize compelling new scientific opportunities for understanding stars and stellar systems that can be enabled by sub-milliarcsec angular resolution, UV/Optical spectral imaging observations. These can reveal details of many dynamic processes that affect stellar formation, structure, and evolution.
  124. Isella, A., Ricci, L., Andrews, S., et al., (including Van Belle, G.), 2019, BAAS, 51, 174, Observing Planetary Systems in the Making
    We discuss science cases to support the development of sub-au imaging capabilities to image forming planets in the terrestrial region of nearby proto-planetary disks.
  125. Burgasser, A., Baraffe, I., Browning, M., et al., (including van Belle, G.), 2019, BAAS, 51, 214, Fundamental Physics with Brown Dwarfs: The Mass-Radius Relation
    The lowest-mass stars, brown dwarfs and giant exoplanets span a minimum in the mass-radius relationship that probes the fundamental physics of extreme states of matter, magnetism, and fusion. This White Paper outlines scientific opportunities and the necessary resources for modeling and measuring the mass- radius relationship in this regime.
  126. Rau, G., Montez, R., Carpenter, K., et al., (including van Belle, G.), 2019, BAAS, 51, 241, Cool, evolved stars: results, challenges, and promises for the next decade
    This White Paper identifies compelling scientific opportunities in the field of Cool, Evolved Stars, describing the observational and theoretical challenges to our understanding, and the key advancements made. We portray the pathway towards understanding, and identify, through recommendations, which advancements are necessary in 2020-2030 & beyond.
  127. Rackham, B., Pinhas, A., Apai, D., et al., (including Llama, J.), 2019, BAAS, 51, 328, Constraining Stellar Photospheres as an Essential Step for Transmission Spectroscopy of Small Exoplanets
    Transmission spectra probe the atmospheres of transiting exoplanets, but these observations are also subject to signals introduced by magnetic active regions on host stars. We outline scientific opportunities in the next decade for providing useful constraints on stellar photospheres for the purposes of exoplanet transmission spectroscopy.
  128. Ridgway, S., Akeson, R., Baines, E., et al., 2019, BAAS, 51, 332, Precision Analysis of Evolved Stars
    The broad recommendation of this paper is three-fold: recognize the essential role of stellar physics in all of astronomy and cosmology; note that a revolution in stellar measurement capabilities, datasets, and modeling is underway and gaining momentum; and support the scientists, their essential technologies and observatories.
  129. Bendek, E., Belikov, R., Guyon, O., et al., (including Van Belle, G.), 2019, BAAS, 51, 354, The value of astrometry for exoplanet science
    We describe the scientific importance of measuring exoplanet masses and how high-precision astrometry can be utilized for this purpose. We describe current technology development efforts and astrometry missions concepts being proposed by the community to detect and characterize exoplanets.
  130. van Belle, G., Baines, E., Boyajian, T., et al., (including von Braun, K.), 2019, BAAS, 51, 381, High Angular Resolution Astrophysics: Fundamental Stellar Parameters
    A discussion of direct determination of fundamental stellar parameters, which has many profound and wide-ranging impacts throughout astrophysics.
  131. Schaefer, G., Duchene, G., Farrington, C., et al., (including Prato, L., van Belle, G.), 2019, BAAS, 51, 483, Binary and Multiple Star Systems at High Angular Resolution
    Binary and multiple star systems provide laboratories for measuring stellar masses and studying star formation, stellar evolution, and dynamical evolution over time. This paper outlines several areas in the context of binary stars that can be advanced over the next decade.
  132. Huber, D., Basu, S., Beck, P., et al., (including van Belle, G.), 2019, BAAS, 51, 488, Stellar Physics and Galactic Archaeology using Asteroseismology in the 2020's
    Asteroseismology is the only observational tool in astronomy that can probe the interiors of stars, and is a benchmark method for deriving fundamental properties of stars and exoplanets. In this white paper, we describe key science questions and necessary facilities to continue the asteroseismology revolution into the 2020's.
  133. Monnier, J., Rau, G., Bermudez, J., et al., (including van Belle, G.), 2019, BAAS, 51, 498, Imaging the Key Stages of Planet Formation
    In this white paper, we explore how higher angular resolution beyond ALMA and 8m-class telescopes can extend our understanding of the key stages of planet formation, to resolve accreting circumplanetary disks themselves, and to watch planets forming in situ for the nearest star-forming regions.
  134. Monnier, J., Rau, G., Baines, E., et al., (including van Belle, G.), 2019, BAAS, 51, 514, The Future of Exoplanet Direct Detection
    Diffraction fundamentally limits our ability to image and characterize exoplanets. Interferometry offers some advantages in exoplanet detection and characterization and we explore in this white paper some of the potential scientific breakthroughs possible.
  135. Thilker, D., Lee, J., Capak, P., et al., (including Hunter, D.), 2019, BAAS, 51, 525, The Nature of Low-Density Star Formation
    How do stars manage to form within low-density, HI-dominated gas? Here we outline fundamental questions about the nature of star formation at low- density. We describe the wide-field, high-resolution imaging of stars, star clusters, and gas clouds in nearby galaxies needed to provide definitive answers and build a complete theory of star formation.
  136. Stern, S., Weaver, H., Spencer, J., et al., (including Grundy, W.), 2019, Sci, 364, aaw9771, Initial results from the New Horizons exploration of 2014 MU69, a small Kuiper Belt object
    The Kuiper Belt is a distant region of the outer Solar System. On 1 January 2019, the New Horizons spacecraft flew close to (486958) 2014 MU69, a cold classical Kuiper Belt object approximately 30 kilometers in diameter. Such objects have never been substantially heated by the Sun and are therefore well preserved since their formation. We describe initial results from these encounter observations. MU69 is a bilobed contact binary with a flattened shape, discrete geological units, and noticeable albedo heterogeneity. However, there is little surface color or compositional heterogeneity. No evidence for satellites, rings or other dust structures, a gas coma, or solar wind interactions was detected. MU69s origin appears consistent with pebble cloud collapse followed by a low-velocity merger of its two lobes.
  137. Hromakina, T., Belskaya, I., Krugly, Y., et al., (including Thirouin, A.), 2019, A&A, 625, A46, Long-term photometric monitoring of the dwarf planet (136472) Makemake

    Aims: We studied the rotational properties of the dwarf planet Makemake.
    Methods: The photometric observations were carried out at different telescopes between 2006 and 2017. Most of the measurements were acquired in BVRI broad-band filters of a standard Johnson-Cousins photometric system.
    Results: We found that Makemake rotates more slowly than was previously reported. A possible lightcurve asymmetry suggests a double-peaked period of P = 22.8266 0.0001 h. A small peak-to-peak lightcurve amplitude in R-filter A = 0.032 0.005 mag implies an almost spherical shape or near pole-on orientation. We also measured BVRI colours and the R-filter phase-angle slope and revised the absolute magnitudes. The absolute magnitude of Makemake has remained unchanged since its discovery in 2005. No direct evidence of a newly discovered satellite was found in our photometric data; however, we discuss the possible existence of another larger satellite.

    Table A.1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr ( or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/625/A46

  138. Navarro-Meza, S., Mommert, M., Trilling, D., et al., (including Moskovitz, N.), 2019, AJ, 157, 190, First Results from the Rapid-response Spectrophotometric Characterization of Near-Earth Objects Using RATIR
    As part of our multi-observatory, multifilter campaign, we present r-i color observations of 82 near-Earth objects (NEOs) obtained with the reionization and transients infrared camera (RATIR) instrument on the 1.5 m robotic telescope at the San Pedro Martirs National Observatory in Mexico. Our project is particularly focused on rapid-response observations of small (850 m) NEOs. The rapid response and the use of spectrophotometry allows us to constrain the taxonomic classification of NEOs with high efficiency. Here we present the methodology of our observations and our result, suggesting that the ratio of C-type to S-type asteroids in a size range of 30-850 m is 1.1, which is in accordance with our previous results. We also find that 10% of all NEOs in our sample are neither C- nor S-type asteroids
  139. Binzel, R., DeMeo, F., Turtelboom, E., et al., (including Burt, B., Moskovitz, N.), 2019, Icar, 324, 41, Compositional distributions and evolutionary processes for the near-Earth object population: Results from the MIT-Hawaii Near-Earth Object Spectroscopic Survey (MITHNEOS)
    Advancing technology in near-infrared instrumentation and dedicated planetary telescope facilities have enabled nearly two decades of reconnoitering the spectral properties for near-Earth objects (NEOs). We report measured spectral properties for more than 1000 NEOs, representing >5% of the currently discovered population. Thermal flux detected below 2.5 m allows us to make albedo estimates for nearly 50 objects, including two comets. Additional spectral data are reported for more than 350 Mars-crossing asteroids. Most of these measurements were achieved through a collaboration between researchers at the Massachusetts Institute of Technology and the University of Hawaii, with full cooperation of the NASA Infrared Telescope Facility (IRTF) on Mauna Kea. We call this project the MIT-Hawaii Near-Earth Object Spectroscopic Survey (MITHNEOS; myth-neos). While MITHNEOS has continuously released all spectral data for immediate use by the scientific community, our objectives for this paper are to: (1) detail the methods and limits of the survey data, (2) formally present a compilation of results including their taxonomic classification within a single internally consistent framework, (3) perform a preliminary analysis on the overall population characteristics with a concentration toward deducing key physical processes and identifying their source region for escaping the main belt. Augmenting our newly published measurements are the previously published results from the broad NEO community, including many results graciously shared by colleagues prior to formal publication. With this collective data set, we find the near-Earth population matches the diversity of the main-belt, with all main-belt taxonomic classes represented in our sample. Potentially hazardous asteroids (PHAs) as well as the subset of mission accessible asteroids (V 7 km/s) both appear to be a representative mix of the overall NEO population, consistent with strong dynamical mixing for the population that interacts most closely with Earth. Mars crossers, however, are less diverse and appear to more closely match the inner belt population from where they have more recently diffused. The fractional distributions of major taxonomic classes (60% S, 20% C, 20% other) appear remarkably constant over two orders of magnitude in size (10 km to 100 m), which is eight orders of magnitude in mass, though we note unaccounted bias effects enter into our statistics below about 500 m. Given the range of surface ages, including possible refreshment by planetary encounters, we are able to identify a very specific space weathering vector tracing the transition from Q- to Sq- to S-types that follows the natural dispersion for asteroid spectra mapped into principal component space. We also are able to interpret a shock darkening vector that may account for some objects having featureless spectra. Space weathering effects for C-types are complex; these results are described separately by Lantz, Binzel, DeMeo. (2018, Icarus 302, 10-17). Independent correlation of dynamical models with taxonomic classes map the escape zones for NEOs to main-belt regions consistent with well established heliocentric compositional gradients. We push beyond taxonomy to interpret our visible plus near-infrared spectra in terms of the olivine and pyroxene mineralogy consistent with the H, L, and LL classes of ordinary chondrites meteorites. Correlating meteorite interpretations with dynamical escape region models shows a preference for LL chondrites to arrive from the 6 resonance and H chondrites to have a preferential signature from the mid-belt region (3:1 resonance). L chondrites show some preference toward the outer belt, but not at a significant level. We define a Space Weathering Parameter as a continuous variable and find evidence for step-wise changes in space weathering properties across different planet crossing zones in the inner solar system. Overall we hypothesize the relative roles of planetary encounters, YORP spin-up, and thermal cycling across the inner solar system.
  140. Lockwood, G., 2019, Icar, 324, 77, Final compilation of photometry of Uranus and Neptune, 1972-2016.
    Photometric observations of Uranus and Neptune made each year since 1972 at Lowell Observatory in the b (472 nm) and y (551 nm) filters of the Stromgren photometric system recorded the mainly seasonal variations of disk-integrated albedos of these objects. The measurements predate Voyager and Hubble Telescope multi-wavelength imaging and overlap more than a decade of ground-based adaptive optics near-IR imaging. This paper is a final archive and brief summarizing discussion of observations through 2016 and includes electronic tables of 360 observations of Uranus and 433 observations of Neptune.
  141. Beyer, R., Spencer, J., McKinnon, W., et al., (including Grundy, W.), 2019, Icar, 323, 16, The nature and origin of Charon's smooth plains
    Charon displays extensive plains that cover the equatorial area and south to the terminator on the sub-Pluto hemisphere observed by New Horizons. We hypothesize that these plains are a result of Charon's global extension and early subsurface ocean yielding a large cryoflow that completely resurfaced this area leaving the plains and other features that we observe today. The cryoflow consisted of ammonia-rich material, and could have resurfaced this area either by cryovolcanic effusion similar to lunar maria emplacement or a mechanism similar to magmatic stoping where lithospheric blocks foundered. Geological observations, modeling of possible flow rheology, and an analysis of rille orientations support these hypotheses.
  142. Cellino, A., Bagnulo, S., Tanga, P., et al., (including Devogele, M.), 2019, MNRAS, 485, 570, Brangane: a new family of Barbarian asteroids
    The so-called Barbarian asteroids [from the name of the prototype of this class, asteroid (234) Barbara] are extremely interesting objects because they might be the survivors of a very early generation of planetesimals. We have identified in the past the first case of an asteroid family (the Watsonia family) whose members are Barbarians, all issued from the collisional disruption of a sizeable parent body. Here we report on the identification of another family, called after the name of its biggest member, asteroid (606) Brangane, consisting of objects displaying the polarimetric properties characterizing the Barbarian behaviour. This is the first recognized case of a swarm of small Barbarians issued from a quite recent cratering event.
  143. van Belle, G., 2019, NatAs, 3, 480, An improved stellar yardstick in the shadows
    Measurement of the diffraction pattern of starlight during an asteroid occultation opens up new territory in stellar angular size determinations.
  144. Moreno, F., Jehin, E., Licandro, J., et al., (including Devogele, M., Moskovitz, N.), 2019, A&A, 624, L14, Dust properties of double-tailed active asteroid (6478) Gault
    Context. Asteroid (6478) Gault was discovered to exhibit a comet-like tail in observations from December 2018, becoming a new member of the so-called active asteroid population in the main asteroid belt.
    Aims: We seek to investigate the grain properties of the dust ejected from asteroid (6478) Gault and to give insight into the activity mechanism(s).
    Methods: We use a Monte Carlo dust tail brightness code to retrieve the dates of dust ejection, the physical properties of the grains, and the total dust mass losses during each event. The code takes into account the brightness contribution of the asteroid itself. The model is applied to a large data set of images spanning the period from 2019 January 11 to 2019 March 13. In addition, we carried out both short- and long-term photometric measurements of the asteroid.
    Results: It is shown that, to date, asteroid (6478) Gault has experienced two episodes of impulsive dust ejection, which took place around 2018 November 5 and 2019 January 2. These two episodes released at least 1.4 107 kg and 1.6 106 kg of dust, respectively, at escape speeds. The size distribution, consisting of particles in the 1 m-1 cm radius range, follows a broken power law with bending points near 15 m and 870 m. On the other hand, the photometric series indicate a nearly constant magnitude over several 5-7.3 h periods, which is a possible effect of the masking of a rotational light curve by the dust.
    Conclusions: The dust particles forming Gault's tails were released from the asteroid at escape speeds, but the specific ejection mechanism is unclear until photometry of the dust-free asteroid are conducted to assess whether this was related to rotational disruption or to other possible causes.
  145. Neugent, K., Levesque, E., Massey, P., et al., 2019, ApJ, 875, 124, Binary Red Supergiants. II. Discovering and Characterizing B-type Companions
    The percentage of massive main-sequence OB stars in binary systems is thought to be as high as 100%. However, very few Galactic binary red supergiants (RSGs) have been identified, despite the fact that these stars are the evolved descendants of OB stars. As shown in our recent paper, binary RSGs will likely have B-type companions, as dictated by stellar evolution considerations. Such a system will have a very unique photometric signature due to the shape of the spectral energy distribution. Using photometric cutoffs, it should therefore be possible to detect candidate RSG+B star binary systems. Here we present our spectroscopic follow-up observations of such candidates. Out of our initial list of 280 candidates in M31 and M33, we observed 149 and confirmed 63 as newly discovered RSG+B star binary systems. Additional spectra of four candidate systems in the Small Magellanic Cloud confirmed all of them as new RSG+B star binaries including the first known RSG+Be star system. By fitting BSTAR06 and MARCS model atmospheres to the newly obtained spectra, we place estimates on the temperatures and subtypes of both the B stars and RSGs. Overall, we have found 87 new RSG+B star binary systems in M31, M33 and the Small and Large Magellanic Clouds. Our future studies are aimed at determining the binary fraction of RSGs.
  146. McNeill, A., Hora, J., Gustafsson, A., et al., (including Mommert, M.), 2019, AJ, 157, 164, Constraining the Shape Distribution of Near-Earth Objects from Partial Light Curves
    In the absence of dense photometry for a large population of near-Earth objects (NEOs), the best method of obtaining a shape distribution comes from sparse photometry and partial light curves. We have used 867 partial light curves obtained by Spitzer to determine a shape distribution for subkilometer NEOs. From this data we find a best-fit average elongation of \tfrac{b}{a}=0.72+/- 0.08. We compare this result with a shape distribution obtained from 1869 NEOs in the same size range observed by Pan-STARRS 1 (PS1) and find the Spitzer-obtained elongation to be in excellent agreement with this PS1 value of \tfrac{b}{a}=0.70+/- 0.10. These values are also in agreement with literature values for 1 < D < 10 km objects in the main asteroid belt, however, there is a size discrepancy between the two data sets. Using a smaller sample of NEOs in the size range of 1 < D < 5 km from PS1 data, we obtain an average axis ratio of b/a = 0.70 0.12. This is more elongated than the shape distribution for main belt objects in the same size regime, although the current uncertainties are sizeable and this should be verified using a larger data set. As future large surveys come online it will be possible to observe smaller main belt asteroids to allow for better comparisons of different subkilometer populations.
  147. DeMeo, F., Polishook, D., Carry, B., et al., (including Burt, B., Moskovitz, N.), 2019, Icar, 322, 13, Olivine-dominated A-type asteroids in the main belt: Distribution, abundance and relation to families
    Differentiated asteroids are rare in the main asteroid belt despite evidence for 100 distinct differentiated bodies in the meteorite record. We have sought to understand why so few main-belt asteroids differentiated and where those differentiated bodies or fragments reside. Using the Sloan Digital Sky Survey (SDSS) to search for a needle in a haystack we identify spectral A-type asteroid candidates, olivine-dominated asteroids that may represent mantle material of differentiated bodies. We have performed a near-infrared spectral survey with SpeX on the NASA IRTF and FIRE on the Magellan Telescope.

    We report results from having doubled the number of known A-type asteroids. We deduce a new estimate for the overall abundance and distribution of this class of olivine-dominated asteroids. We find A-type asteroids account for less than 0.16% of all main-belt objects larger than 2 km and estimate there are a total of 600 A-type asteroids above that size. They are found rather evenly distributed throughout the main belt, are even detected at the distance of the Cybele region, and have no statistically significant concentration in any asteroid family. We conclude the most likely implication is the few fragments of olivine-dominated material in the main belt did not form locally, but instead were implanted as collisional fragments of bodies that formed elsewhere.

  148. Bird, M., Linscott, I., Tyler, G., et al., (including Grundy, W.), 2019, Icar, 322, 192, Radio thermal emission from Pluto and Charon during the New Horizons encounter
    One component of the REX instrument on NASA's New Horizons spacecraft was an investigation of the radio continuum radiation from Pluto and Charon during the flyby on 14 July 2015. The planetary thermal emission was recorded at a wavelength of 4.17 cm (7.18 GHz) during approach, departure, and specifically on the non-illuminated hemispheres of Pluto and Charon during the respective intervals between occultation ingress and egress. We derive the brightness temperatures for these disk-resolved and unresolved observations. The mean values and 1 deviations of brightness temperature for the unresolved sunlit disk are 33.2 1.4 K and 47.2 5.3 K for Pluto and Charon, respectively, consistent with the global albedos of the two bodies as well as with previous ground-based estimates at smaller wavelengths. A slightly colder temperature of 29.0 2.5 K was determined for the disk-integrated nightside of Pluto and a larger drop in temperature was observed for Charon (40.9 0.9 K), implying a smaller thermal inertia for Charon than Pluto. The measured brightness temperature of Pluto across the nightside diametric scan reached a maximum of 29.0 1.5 K in the center of the disk. The profile shape is attributed to an emissivity effect, which favors thermal emission toward higher elevation angles. As a first approximation, the effective emissivity for thermal emission is calculated for the case when Pluto and Charon are uniformly smooth homogenous spheres. Under this assumption, the effective emissivity for these observations is close to unity for all probable surface constituents, implying that the effective temperature of the Pluto subsurface is only a few percent higher than the observed brightness temperature. A considerably lower subsurface emissivity is implied, however, if the higher atmospheric temperatures near the surface determined from the REX occultation measurements are also valid for the subsurface.
  149. Cook, D., Lee, J., Adamo, A., et al., (including Hunter, D.), 2019, MNRAS, 484, 4897, Star cluster catalogues for the LEGUS dwarf galaxies
    We present the star cluster catalogues for 17 dwarf and irregular galaxies in the HST Treasury Program `Legacy ExtraGalactic UV Survey' (LEGUS). Cluster identification and photometry in this sub-sample are similar to that of the entire LEGUS sample, but special methods were developed to provide robust catalogues with accurate fluxes due to low cluster statistics. The colours and ages are largely consistent for two widely used aperture corrections, but a significant fraction of the clusters are more compact than the average training cluster. However, the ensemble luminosity, mass, and age distributions are consistent suggesting that the systematics between the two methods are less than the random errors. When compared with the clusters from previous dwarf galaxy samples, we find that the LEGUS catalogues are more complete and provide more accurate total fluxes. Combining all clusters into a composite dwarf galaxy, we find that the luminosity and mass functions can be described by a power law with the canonical index of -2 independent of age and global SFR binning. The age distribution declines as a power law, with an index of - 0.80 0.15, independent of cluster mass and global SFR binning. This decline of clusters is dominated by cluster disruption since the combined star formation histories and integrated-light SFRs are both approximately constant over the last few hundred Myr. Finally, we find little evidence for an upper-mass cut-off (<2) in the composite cluster mass function, and can rule out a truncation mass below 104.5M but cannot rule out the existence of a truncation at higher masses.
  150. Lachaume, R., Rabus, M., Jordan, A., et al., (including von Braun, K.), 2019, MNRAS, 484, 2656, Towards reliable uncertainties in IR interferometry: the bootstrap for correlated statistical and systematic errors
    We propose a method to overcome the usual limitation of current data processing techniques in optical and infrared long-baseline interferometry: most reduction pipelines assume uncorrelated statistical errors and ignore systematics. We use the bootstrap method to sample the multivariate probability density function of the interferometric observables. It allows us to determine the correlations between statistical error terms and their deviation from a Gaussian distribution. In addition, we introduce systematics as an additional, highly correlated error term whose magnitude is chosen to fit the data dispersion. We have applied the method to obtain accurate measurements of stellar diameters for underresolved stars, i.e. smaller than the angular resolution of the interferometer. We show that taking correlations and systematics has a significant impact on both the diameter estimate and its uncertainty. The robustness of our diameter determination comes at a price: we obtain 4 times larger uncertainties, of a few per cent for most stars in our sample.
  151. Rabus, M., Lachaume, R., Jordan, A., et al., (including von Braun, K.), 2019, MNRAS, 484, 2674, A discontinuity in the Teff-radius relation of M-dwarfs
    We report on 13 new high-precision measurements of stellar diameters for low-mass dwarfs obtained by means of near-infrared long-baseline interferometry with PIONIER at the Very Large Telescope Interferometer. Together with accurate parallaxes from Gaia DR2, these measurements provide precise estimates for their linear radii, effective temperatures, masses, and luminosities. This allows us to refine the effective temperature scale, in particular towards the coolest M-dwarfs. We measure for late-type stars with enhanced metallicity slightly inflated radii, whereas for stars with decreased metallicity we measure smaller radii. We further show that Gaia DR2 effective temperatures for M-dwarfs are underestimated by 8.2 per cent and give an empirical MG-Teff relation that is better suited for M-dwarfs with Teff between 2600 and 4000 K. Most importantly, we are able to observationally identify a discontinuity in the Teff-radius plane, which is likely due to the transition from partially convective M-dwarfs to the fully convective regime. We found this transition to happen between 3200 and 3340 K, or equivalently for stars with masses { } 0.23 M_{\odot }. We find that in this transition region the stellar radii are in the range from 0.18 to 0.42 R\odot for similar stellar effective temperatures.
  152. Hanley, J., 2019, absc, 510-6, Chlorine Salts and Their Effect on Habitability Across the Solar System
    Chlorine salts lower the freezing point of water, lower the evaporation rate of salt solutions, and can significantly lower the activity of water when sufficiently concentrated. I will discuss the presence of chlorine salts across the solar system and their effect on habitability on those bodies.
  153. West, M., De Propris, R., Bremer, M., et al., 2019, NatAs, 3, 362, Publisher Correction: Ten billion years of brightest cluster galaxy alignments
    When this Letter was originally published, Supplementary Table 1 was mistakenly omitted; it is now available at 10.1038/s41550-019-0728-9.
  154. Oszkiewicz, D., Kryszczynska, A., Kankiewicz, P., et al., (including Moskovitz, N., Skiff, B., Leith, T.), 2019, A&A, 623, A170, Physical and dynamical properties of the unusual V-type asteroid (2579) Spartacus
    Context. Asteroid (2579) Spartacus is a small V-type object located in the inner main belt. This object shows spectral characteristics unusual for typical Vestoids, which may indicate an origin deeper than average within Vesta or an origin from an altogether different parent body.
    Aims: Our main goal is to study the origin of Spartacus. We derive the spin of Spartacus and a convex shape model of Spartacus in order to increase the knowledge of the body's physical properties. The rotational parameters are then used to investigate dynamical evolution of the object as well as to distinguish regions sampled by spectral observations to determine whether its surface displays heterogeneity.
    Methods: We collected lightcurves available from the literature (oppositions of 2009, 2012) and obtained additional photometric observations at various telescopes in 2016, 2017, and 2018. We used the lightcurve inversion method to derive a spin and convex shape model. We have collected spectral observations over two rotational periods of Spartacus and determined its spectral parameters using the modified Gaussian model (MGM). We then dynamically integrated the orbital elements of Spartacus, taking into account existing information, including its thermal properties, size and the derived spin axis orientation.
    Results: We find two models for (2579) Spartacus: (a) = 312 5, = -57 5 and (b) = 113 5, = -60 5 both retrograde. We find that the drift direction for Spartacus is consistent with separation from Vesta, and after a backward integration of 1 Gyr the asteroid reaches the boundary of the family. We did not observe spectral variations with rotation, thus the body most likely has a homogeneous surface. Additionally, new spectral analysis indicates that the 1.0 and 2.0 m band centers are within ranges that are typical for Vestoids while the area ratio of these bands is about half that of typical Vestoids.
    Conclusions: The asteroid (2579) Spartacus is in retrograde rotation and has a drift direction consistent with an origin from Vesta. The revised spectral band centers are within ranges typical for Vestoids, while band area ratio (BAR) is unusually low compared to that of other V-types. The dynamical model shows that the asteroid could have migrated to its current location from the edges of the Vesta family within 1 Gyr, but an origin from an earlier impact on Vesta could also be plausible.
  155. Buratti, B., Hicks, M., Hillier, J., et al., (including Grundy, W.), 2019, ApJL, 874, L3, New Horizons Photometry of Pluto's Moon Charon
    The New Horizons spacecraft extended the range in solar phase angle coverage for Plutos moon Charon from 1.8the maximum observable from Earthto 170. This extraordinary expansion in range has enabled photometric modeling and a robust determination of Charons phase integral and Bond albedo at visible wavelengths. Photometric modeling shows that Charon is similar in its photometric properties to other icy moons, except that its single particle phase function is more isotropic, suggesting the Kuiper Belt may represent a new regime for surface alteration processes. Charons phase integral is 0.70 0.04 and its Bond albedo is 0.29 0.05.
  156. Wood, C., Boyajian, T., von Braun, K., et al., 2019, ApJ, 873, 83, Benchmarking Substellar Evolutionary Models Using New Age Estimates for HD 4747 B and HD 19467 B
    Constraining substellar evolutionary models (SSEMs) is particularly difficult due to a degeneracy between the mass, age, and luminosity of a brown dwarf. In cases where a brown dwarf is found as a directly imaged companion to a star, as in HD 4747 and HD 19467, the mass, age, and luminosity of the brown dwarf are determined independently, making them ideal objects to use to benchmark SSEMs. Using the Center for High Angular Resolution Astronomy Array, we measured the angular diameters and calculated the radii of the host stars HD 4747 A and HD 19467 A. After fitting their parameters to the Dartmouth Stellar Evolution Database, MESA Isochrones and Stellar Tracks, and Yonsei-Yale isochronal models, we adopt age estimates of {10.74}-6.87+6.75 Gyr for HD 4747 A and {10.06}-0.82+1.16 Gyr for HD 19467 A. Assuming the brown dwarf companions HD 4747 B and HD 19467 B have the same ages as their host stars, we show that many of the SSEMs under-predict bolometric luminosities by 0.75 dex for HD 4747 B and 0.5 dex for HD 19467 B. The discrepancies in luminosity correspond to over-predictions of the masses by 12% for HD 4747 B and 30% for HD 19467 B. We also show that SSEMs that take into account the effect of clouds reduce the under-prediction of luminosity to 0.6 dex and the over-prediction of mass to 8% for HD 4747 B, an L/T transition object that is cool enough to begin forming clouds. One possible explanation for the remaining discrepancies is missing physics in the models, such as the inclusion of metallicity effects.
  157. Singer, K., McKinnon, W., Gladman, B., et al., (including Grundy, W.), 2019, Sci, 363, 955, Impact craters on Pluto and Charon indicate a deficit of small Kuiper belt objects
    The flyby of Pluto and Charon by the New Horizons spacecraft provided high-resolution images of cratered surfaces embedded in the Kuiper belt, an extensive region of bodies orbiting beyond Neptune. Impact craters on Pluto and Charon were formed by collisions with other Kuiper belt objects (KBOs) with diameters from ~40 kilometers to ~300 meters, smaller than most KBOs observed directly by telescopes. We find a relative paucity of small craters 13 kilometers in diameter, which cannot be explained solely by geological resurfacing. This implies a deficit of small KBOs (1 to 2 kilometers in diameter). Some surfaces on Pluto and Charon are likely 4 billion years old, thus their crater records provide information on the size-frequency distribution of KBOs in the early Solar System.
  158. Ginsburg, A., Sipocz, B., Brasseur, C., et al., (including Mommert, M.), 2019, AJ, 157, 98, astroquery: An Astronomical Web-querying Package in Python
    astroquery is a collection of tools for requesting data from databases hosted on remote servers with interfaces exposed on the internet, including those with web pages but without formal application program interfaces. These tools are built on the Python requests package, which is used to make HTTP requests, and astropy, which provides most of the data parsing functionality. astroquery modules generally attempt to replicate the web page interface provided by a given service as closely as possible, making the transition from browser-based to command-line interaction easy. astroquery has received significant contributions from throughout the astronomical community, including several from telescope archives. astroquery enables the creation of fully reproducible workflows from data acquisition through publication. This paper describes the philosophy, basic structure, and development model of the astroquery package. The complete documentation for astroquery can be found at http://astroquery.readthedocs.io/.
  159. Schleicher, D., Knight, M., Eisner, N., et al., (including Thirouin, A.), 2019, AJ, 157, 108, Gas Jet Morphology and the Very Rapidly Increasing Rotation Period of Comet 41P/Tuttle-Giacobini-Kresak
    We present results from our 47 night imaging campaign of Comet 41P/Tuttle-Giacobini-Kresak conducted from Lowell Observatory between 2017 February 16 and July 2. Coma morphology revealed gas jets, whose appearance and motion as a function of time yielded the rotation period and other properties. All narrowband CN images exhibited either one or two jets; one jet appeared as a partial face-on spiral with clockwise rotation, while the second jet evolved from a side-on corkscrew, through face-on, to corkscrew again, with only a slow evolution throughout the apparition due to progressive viewing geometry changes. A total of 78 period determinations were made over a 7 week interval, yielding a smooth and accelerating rotation period starting at 24 hr (March 21 and 22) and passing 48 hr on April 28. While this is by far the fastest rate of change ever measured for a comet nucleus, the torque required is readily within what can exist given likely properties of the nucleus. If the torque remained constant, we estimate that the nucleus could have stopped rotating and/or begun to tumble as soon as only 2 months following perihelion and will certainly reach this stage by early in the next apparition. Working backward in time, Tuttle-Giacobini-Kresak would have been rotating near its rotational breakup velocity three to four orbits earlier, suggesting that its extreme 7 mag outburst observed in 2001 might have been caused by a partial fragmentation at that time, as might the pair of 1973 8 mag outbursts if there had been an earlier spin-down and spin-up cycle.
  160. Sickafoose, A., Bosh, A., Levine, S., et al., 2019, Icar, 319, 657, A stellar occultation by Vanth, a satellite of (90482) Orcus
    A stellar occultation by the large trans-Neptunian object (90482) Orcus was predicted to occur on 2017 March 07. Observations were made at five sites in North and South America: the 0.6-m Astronomical Telescope of the University of Stuttgart (ATUS) at Sierra Remote Observatories, California; Las Cumbres Observatory's 1-m telescope at McDonald Observatory, Fort Davis, Texas (ELP); NASA's 3-m InfraRed Telescope Facility (IRTF) on Mauna Kea, Hawai'i; the 0.6-m Southeastern Association for Research in Astronomy (SARA-CT) telescope at Cerro Tololo, Chile; and the 4.1-m Southern Astrophysical Research (SOAR) telescope on Cerro Pachon, Chile. High-speed, visible-wavelength images were taken at all sites, in addition to simultaneous K-band images at the IRTF. Solid-body occultations were observed from two sites. Post-event reconstruction suggested an occultation of two different stars observed from two different sites. Follow-up, speckle imaging revealed a second star, which verified that the occulting body in both cases was Orcus' satellite, Vanth. The two single-chord detections, with an anomalously large timing delay in one chord, have lengths of 291 125 km and 434.4 2.4 km. The observations, combined with a non-detection at a nearby site, allow a tight constraint of 443 10 km to be placed on Vanth's size (assuming it is spherical). A 3- upper limit of 1-4 bar (depending on constituent) is found for a global Vanth atmosphere. The immersion and emersion profiles are slightly different, with atmospheric constraints 40% higher on immersion than on emersion. No rings or other material were detected within ten thousand kms of Vanth, and beyond 8010 km from Orcus, to the tightest optical depth limit of 0.1 at 5 km scale. The occultation probed as close as 5040 km from Orcus, placing an optical depth limit of 0.3 at 5 km scale on any encircling material at that distance.
  161. Chuss, D., Andersson, B., Bally, J., et al., (including Hamilton, R.), 2019, ApJ, 872, 187, HAWC+/SOFIA Multiwavelength Polarimetric Observations of OMC-1
    We report new polarimetric and photometric maps of the massive star-forming region OMC-1 using the HAWC+ instrument on the Stratospheric Observatory for Infrared Astronomy. We present continuum polarimetric and photometric measurements of this region at 53, 89, 154, and 214 m at angular resolutions of 5, 8, 14, and 19 for the four bands, respectively. The photometric maps enable the computation of improved spectral energy distributions for the region. We find that at the longer wavelengths, the inferred magnetic field configuration matches the hourglass configuration seen in previous studies, indicating magnetically regulated star formation. The field morphology differs at the shorter wavelengths. The magnetic field inferred at these wavelengths traces the bipolar structure of the explosive Becklin-Neugebauer/Kleinman-Low outflow emerging from OMC-1 behind the Orion Nebula. Using statistical methods to estimate the field strength in the region, we find that the explosion dominates the magnetic field near the center of the feature. Farther out, the magnetic field is close to energetic equilibrium with the ejecta and may be providing confinement to the explosion. The correlation between polarization fraction and the local polarization angle dispersion indicates that the depolarization as a function of unpolarized intensity is a result of intrinsic field geometry as opposed to decreases in grain alignment efficiency in denser regions.
  162. Horch, E., Tokovinin, A., Weiss, S., et al., (including van Belle, G.), 2019, AJ, 157, 56, Observations of Binary Stars with the Differential Speckle Survey Instrument. VIII. Measures of Metal-poor and Triple Stars from 2015 to 2018
    We present 248 speckle observations of 43 binary and 19 trinary star systems chosen to make progress in two main areas of investigation: the fundamental properties of metal-poor stars and star formation mechanisms. The observations were taken at the Gemini North and South telescopes during the period 2015 July to 2018 April, mainly with the Differential Speckle Survey Instrument but also with a few early results from the new Alopeke speckle camera at Gemini North. We find that the astrometry and photometry of these observations as a whole are consistent with previous work at Gemini. We present five new visual orbits for systems important in understanding metal-poor stars, three of which have orbital periods of less than 4 yr, and we indicate the degree to which these and future observations can impact our knowledge of stellar properties and star formation. In particular, we find a decrease in mass at fixed spectral type for metal-poor stars versus their solar-metallicity analogs that is consistent with predictions that are made from current stellar models.
  163. Robbins, S., Beyer, R., Spencer, J., et al., (including Grundy, W.), 2019, JGRE, 124, 155, Geologic Landforms and Chronostratigraphic History of Charon as Revealed by a Hemispheric Geologic Map
    Geologic mapping has been used for over 200 years as a technique to synthesize a complicated surface into a more simplified product, identifying similar types of surface features, and placing them into a relative stratigraphy. Geomorphologic mapping has applied those principles to other terrestrial bodies throughout the solar system and has formed an important product set to understand these surfaces, plan future exploration, and conduct different scientific endeavors. We created a geomorphologic map of the New Horizons encounter hemisphere of Pluto's binary companion, Charon. Ten primary geomorphologic unit categories were identified, covering approximately 35% of Charon's surface, and we used lower resolution data to speculate about other regions of Charon. Over 1,000 linear features were mapped, nearly 90% of them are tectonic in nature, and we use these to provide evidence of Charon being active in its past. Additionally, we placed the mapped features into a chronostratigraphic sequence, and we present a possible surface history for the body. The northern terrain typified by large crustal blocks is the oldest, having fractured early in Charon's history, and potentially similar blocks were submerged in a cryoflow of which the now solid surface of Vulcan Planitia is the remnant today.
  164. Powell, E., Horanzy, R., Schutte, M., et al., (including Skiff, B.), 2019, AAS, 233, 163.10, Characterizing Changes in the Be Star Population of NGC 663
    Characterizing the amplitude and wavelength dependence of variations in the intrinsic polarization of classical Be stars can help inform how these circumstellar disks change over time. Since the observed polarization is a superposition of a component arising from the interstellar medium (ISP) and a component intrinsic to the Be star itself, robustly determining the ISP component is critical to isolating the intrinsic component. We present our analysis of multi-epoch, multi-wavelength photometric and polarimetric imaging of NGC 663. NGC 663 is an open cluster that is known to host a large population of Be stars. We use GAIA Data Release 2 to refine the distance and membership of NGC 663, and use these results to construct a refined field star polarization map towards the cluster, thereby enabling us to better quantify the ISP along the line of sight. This program is supported by NSF-AST 1411563, 1412110, and 1412135, along with the NSF REU program at the University of Oklahoma.
  165. Thilker, D., Lee, J., Rafelski, M., et al., (including Hunter, D.), 2019, AAS, 233, 443.10, Enabling Efficient HST UV Exploration of the Low Surface Brightness Universe
    We present a pilot program with HST to broadly enable high-resolution UV exploration of star formation at low densities in nearby galaxies using a strategy to increase observing efficiency by up to a factor of two. The increased efficiency achieved with WFC3's eXtra-wide filter set makes more tractable programs which require several tens to hundreds of orbits to aggregate sufficient numbers of resolved massive stars, young star clusters, and clumps to build statistical samples. We aim to enable basic characterization of the ensemble properties of star formation in the low density regime in its primary units. We will discuss first results based on a Local Volume dwarf galaxy (Holmberg I) and a more distant low surface brightness spiral (UGC 9024).
  166. Jones, T., Dowell, C., Lopez Rodriguez, E., et al., (including Hamilton, R.), 2019, ApJL, 870, L9, SOFIA Far-infrared Imaging Polarimetry of M82 and NGC 253: Exploring the Supergalactic Wind
    We present far-infrared polarimetry observations of M82 at 53 and 154 m and NGC 253 at 89 m, which were taken with High-resolution Airborne Wideband Camera-plus (HAWC+) in polarimetry mode on the Stratospheric Observatory for Infrared Astronomy. The polarization of M82 at 53 m clearly shows a magnetic field geometry perpendicular to the disk in the hot dust emission. For M82 the polarization at 154 m shows a combination of field geometry perpendicular to the disk in the nuclear region, but closer to parallel to the disk away from the nucleus. The fractional polarization at 53 m (154 m) ranges from 7% (3%) off nucleus to 0.5% (0.3%) near the nucleus. A simple interpretation of the observations of M82 invokes a massive polar outflow, dragging the field along, from a region 700 pc in diameter that has entrained some of the gas and dust, creating a vertical field geometry seen mostly in the hotter (53 m) dust emission. This outflow sits within a larger disk with a more typical planar geometry that more strongly contributes to the cooler (154 m) dust emission. For NGC 253, the polarization at 89 m is dominated by a planar geometry in the tilted disk, with weak indication of a vertical geometry above and below the plane from the nucleus. The polarization observations of NGC 253 at 53 m were of a insufficient signal-to-noise ratio for a detailed analysis.
  167. Karnath, N., Prchlik, J., Gutermuth, R., et al., (including Allen, T.), 2019, ApJ, 871, 46, The Dynamics, Structure, and Fate of a Young Cluster during Gas Dispersal: Hectoschelle, Chandra, Spitzer, and Gaia Observations of Cep OB3b
    We present a study of the kinematics and structure of the Cep OB3b cluster based on new spectra obtained with the Hectoschelle spectrograph on the MMT and data from Spitzer, Chandra, and Gaia. At a distance of 819 16 pc, Cep OB3b is one of the closest examples of a young (3-5 Myr), large (3000 total members) cluster at the late stages of gas dispersal. The cluster is broken into two subclusters surrounded by a lower density halo. We fit the empirical density law of King to each subcluster to constrain their sizes and structure. The richer eastern subcluster has circular symmetry, a modest central density, and lacks molecular gas toward its core, suggesting it has undergone expansion due to gas dispersal. In contrast, the western subcluster deviates from circular symmetry, has a smaller core size, and contains significant molecular gas near its core, suggesting that it is in an earlier phase of gas dispersal. We present posterior probability distributions for the velocity dispersions from the Hectoschelle spectra. The east will continue to expand and likely form a bound cluster with 35% of stars remaining. The west is undergoing slower gas dispersal and will potentially form a bound cluster with 75% of stars remaining. If the halo dissipates, this will leave two independent clusters with 300 members; proper motions suggest that the two subcluster are not bound to each other.
  168. Schindler, K., Buckingham, W., 2019, AAS, 233, 135.06, Apollo Astronaut Training at Arizona's Observatories
    As part of their training to explore the Moon, Apollo astronauts visited several astronomical observatories in Arizona, including Lowell, Kitt Peak, the Naval Observatory Flagstaff Station (NOFS) and the campus observatory at Arizona State College (now Northern Arizona University - NAU). This involved comparing live observations of the Moon through telescopes with photographs of the lunar surface, as well as studying charts to familiarize themselves with the depiction of topographic features. The first of this training occurred in January 1963, when the Next 9 group of astronauts traveled to Flagstaff. They visited Meteor Craterto study an impact crater like they would see on the Moonand Sunset Crater to explore volcanic structures. They then headed to Lowell Observatory to learn about the lunar mapping being carried out there by the Aeronautical Chart and Information Center (ACIC), a branch of the United States Air Force. Later, the astronauts split into three groups for viewing the Moon through telescopes, with one group staying at Lowell, another going to the campus observatory, and the third heading to NOFS. The following year, several smaller groups of astronauts, representing the first three classes, went to Kitt Peak during trips that also saw them study geology elsewhere in the state. At Kitt Peak they enjoyed the unusual opportunity of viewing the Moon through the McMath-Pierce Solar Telescope.
  169. Nofi, L., Prato, L., Johns-Krull, C., et al., (including Llama, J., Sullivan, K., Skiff, B., Biddle, L.), 2019, AAS, 233, 140.25, Preliminary Results from a Young Exoplanet RV Survey
    Observing and characterizing newly-formed planets around young stars is important for developing planet formation and evolution theory. However, given challenges in detecting young planetary systems, current models are primarily based on systems that are billions of years old. It is therefore unclear which exoplanetary properties are indicators of formation conditions, or of later evolution. We are conducting an infrared radial velocity survey to detect and confirm young exoplanets around T Tauri stars using the Immersion Grating Infrared Spectrograph (IGRINS) on the 4.3-m Lowell Observatory Discovery Channel Telescope (DCT). IGRINS simultaneously observes H- and K-bands at a resolution of ~45,000. Infrared spectroscopy is less susceptible to apparent RV variability caused by starspots on active young stars than optical observations. Our sample consists of ~100 T Tauri stars of age 1 to a few Myr in the relatively nearby Taurus star forming region. We present early results on our search for RV variability of T Tauri stars, indicative of the presence of hot Jupiters with the IGRINS + DCT system.
  170. Jacoby, G., Davis, B., Ciardullo, R., et al., 2019, AAS, 233, 150.05, The Progenitor Mass of the Planetary Nebula in the M31 Open Cluster B477-D075
    Using HST/STIS, we have obtained spectra of a planetary nebula that appears to be a member of the M31 open cluster B477-D075 (Bond 2015). The spectra, combined with the [O III] 5007 flux measured from HST archival imaging (Massey, HST program 9794), and corrected for extinction using the STIS spectra, provide sufficient constraints on a Cloudy photoionization model (Ferland et al. 2013) to derive the central-star mass. That mass (~0.7 Msun) corresponds to a progenitor mass of ~3.0 Msun according to a theoretical initial-mass/final-mass relation derived from the stellar-evolution models of Miller Bertolami (2016). This mass is in good agreement with a main-sequence turnoff mass of ~3.3 Msun derived from isochrone fitting to photometry (PHAT project, Dalcanton et al. 2012) of the 350 Myr-old host cluster. This consistency provides strong evidence that the planetary nebula is truly a member of the cluster. We also derive very approximate chemical abundances for oxygen and nitrogen. This work was supported in part by STScI grant HST-GO-14794.003-A.
  171. Dey, J., Crocker, A., Jacoby, G., 2019, AAS, 233, 150.15, Identifying Binary Central Stars of Planetary Nebulae with PSF Fitting
    Ground-based observations find that about 15% of central stars of PNe are close binaries. Kepler light curves were successful in finding periodic variation in four out of six PNe targets in the original Kepler mission (De Marco et al. 2015), suggesting that 67% of the central stars are binaries. The 140 PNe in the K2 campaign 11 field provide an excellent sample size and suggest a binary fraction of about 20-25%, but these targets are in very crowded fields. Consequently, the K2 measuring aperture of 8-10 arcsec obscures the source of the variations since they could come from the PNe central star or from neighboring unrelated stars. We used point spread function (PSF) fitting photometry on the K2 data to try to improve the light curves beyond those from the Kepler pipeline, and to separate the light curves on a star-by-star basis. Use of the PSF fitting method yielded results consistent with the central star being the variable for 5/45 targets and inconclusive findings for the other 40 targets. PSF photometry successfully separated nearby stars, however, hard-to-remove systematic trends were exacerbated, hampering our effort to improve over the Kepler pipeline's original light curves.
  172. Graham, S., Prato, L., Schaefer, G., et al., (including Nofi, L.), 2019, AAS, 233, 155.05, H Band Observations of the Candidate Young Spectroscopic Binary UY Auriga B and its Disk
    Binaries dominate the stellar census; understanding disk evolution in these complex environments is crucial in order to form a complete and accurate model for planet formation. UY Auriga is a ~2 Myr old classical T Tauri binary with a separation of ~0.9". The system contains a number of complex gas-dust interactions between the circumbinary and circumstellar disks. Multiple epochs of high-resolution H-band spectroscopy show that UY Aur B exhibits extreme spectral variability over a period of 13 years or more; it is also known to be highly photometrically variable. We explore whether UY Aur B might itself be a close, short-period binary and provide estimates of accretion properties and possible orbital solutions and component mass ratios.
  173. van Belle, G., Patane, S., Riley, D., et al., 2019, AAS, 233, 158.25, Optimast Structurally Connected Interferometry Enabled by In-Space Robotic Manufacturing and Assembly
    Future goals for astrophysics at the frontiers of high spatial resolution drive the need for large effective apertures beyond what the current generation of space observatories provides. Space-based interferometry delivers on this promise and enables cost-effective observation of faint objects at unprecedented levels of angular resolution. Using the Made In Space (MIS) Optimast capability, a simple, two aperture Structurally Connected Interferometer (SCI) is produced via in-space Additive Manufacturing (AM) technology. This capability allows the two modest apertures to be packaged efficiently for launch and then placed at a large separation, coherently, in order to achieve a greater effective angular resolution . Optimast enables the manufacturing and deployment of large primary trusses unconstrained by launch loads or volume restrictions that meet science requirements for the high angular resolutions (in the milliarcsecond regime) necessary for applications such as characterization of planets near bright stars, and measurement individual objects in dense star clusters. Space-based deployment of an interferometer unfettered by the turbulent atmosphere will markedly increase the sensitivity reach of such an instrument relative to its ground-based counterparts. Adapting the MIS Optimast technology to produce long baseline structures with low thermal expansion materials enables simultaneous structural fabrication and positioning of the optical subsystems to the required static, thermal deflection, and oscillation tolerances. An Optimast-SCI baseline structure eliminates parasitic mass and provides superior absolute position control over traditional deployable structures at much lower cost, mass, and integration complexity.
  174. Llama, J., Cabrera, T., Luna, J., et al., (including Nofi, L.), 2019, AAS, 233, 247.32, Detection of water in the atmosphere of the hot Jupiter HD 102195b
    The composition and structure of hot Jupiter atmospheres provide a fossil record of their primordial origins, potentially holding the key to distinguishing between the various proposed formation mechanisms. High-resolution spectroscopic observations of exoplanet atmospheres enable us to resolve molecular bands into many individual spectral lines in a pattern that is unique to each molecule. By then exploiting the Doppler shift of the planet over multiple nights we can separate the planet spectrum from that of the host star and Earths atmosphere. Here, we use the high-resolution infrared spectrograph IGRINS (R=45,000, =1.4-2.5 microns) on the 4.3m Discovery Channel Telescope to observe the spectrum of the hot Jupiter HD 102195b. Our analysis reveals a 4 detection of water in the atmosphere of this heavily irradiated hot Jupiter.
  175. Prato, L., Nofi, L., 2019, AAS, 233, 254.03, The Lowell Observatory Predoctoral Scholar Program
    Lowell Observatory is pleased to solicit applications for our Predoctoral Scholar Fellowship Program. Now beginning its eleventh year, this program is designed to provide unique research opportunities to graduate students in good standing, currently enrolled at Ph.D. granting institutions. Lowell staff research spans a wide range of topics, from astronomical instrumentation, to icy bodies in our solar system, exoplanet science, stellar populations, star formation, and dwarf galaxies. Active collaborations, the new Ph.D. program at Northern Arizona University, and strong, cooperative links across the greater Flagstaff astronomical community create an exciting, multi-institutional locus in northern Arizona. Lowell Observatory's new 4.3 meter Discovery Channel Telescope is operating at full science capacity and boasts some of the most cutting-edge and unique instrumentation available in optical/infrared astronomy. Student research is expected to lead to a thesis dissertation appropriate for graduation at the doctoral level at the student's home institution. For more information, see http://www2.lowell.edu/rsch/predoc.php and links therein. Applications for Fall 2019 are due by May 1, 2019; alternate application dates will be considered on an individual basis.
  176. Lewis, B., Stansberry, J., Holler, B., et al., (including Grundy, W.), 2019, AAS, 233, 255.12, Distribution and Energy Balance of Pluto's Nitrogen Ice, as seen by New Horizons in 2015
    Pluto's surface is geologically complex, to a significant extent because of volatile ice frosts that are mobile on seasonal and longer time scales. Here, we analyze New Horizons LEISA spectral data to globally map the nitrogen ice, including nitrogen with methane diluted in it, in order to learn about the seasonal processes influencing ice redistribution, and to calculate the globally averaged energy balance. We take advantage of the shifted bands of methane in solid solution with nitrogen, which are much stronger than the 2.15-micron nitrogen band, to more completely map the distribution of the nitrogen ice. We present the resulting maps of the encounter-hemisphere distribution of nitrogen, as well as characterization of its average latitudinal dependence and an examination of how the distribution at the global scale depends on topography. We also use the encounter-hemisphere distribution of nitrogen ice to infer the latitudinal distribution of nitrogen over the rest of Pluto, allowing us to calculate the global energy balance. Under the assumption that Pluto's nitrogen-dominated 11.5 microbar atmosphere is in vapor-pressure equilibrium with the nitrogen ice, the ice temperature is 37.180.10 K. Combined with our global energy balance calculation, this implies that the average bolometric emissivity of Pluto's nitrogen ice is probably in the range 0.5 - 0.9, and that there is a significant reservoir of N2 ice in the un-illuminated areas south of -38 latitude. The global pattern of volatile transport at the time of the encounter was from north to south, with condensation of volatile ices likely occurring southward from approximately Pluto's equator (including in the un-illuminated regions south of -38 latitude). The transition between condensation and sublimation within Sputnik Planitia is correlated with changes in the grain size and CH4 concentration derived from the spectral maps. The low emissivity of Pluto's N2 ice suggests that Pluto's atmosphere may undergo an extended period of constant pressure even as Pluto recedes from the Sun in its orbit.
  177. Clark, C., van Belle, G., Horch, E., et al., (including von Braun, K.), 2019, AAS, 233, 259.03, The POKEMON Speckle Survey of Nearby M-dwarfs
    The POKEMON (Pervasive Overview of Kompanions of Every M-dwarf in Our Neighborhood) survey of nearby M-dwarfs intends to inspect, at diffraction-limited resolution, every low-mass star out to 15pc, along with selected additional objects to 25pc. The primary emphasis of the survey is the detection of low-mass companions to these M-dwarfs for refinement of the low-mass star multiplicity rate. Given the priority these targets will have for upcoming exoplanet studies using TESS and JWST - and the degree to which initially undetected multiplicity has affected Kepler results - a comprehensive survey of our nearby low-mass neighbors will produce a homogenous, complete catalog of fundamental utility. Prior knowledge of those secondary objects - or robust non-detections, as will be captured by this survey - will help immediately clarify the nature of exoplanet transit detections from these current and upcoming missions. POKEMON is using Lowell Observatory's 4.3-m Discovery Channel Telescope (DCT) with the Differential Speckle Survey Instrument (DSSI) speckle camera, along with the NN-Explore Exoplanet Stellar Speckle Imager (NESSI) speckle imager on 3.5-m WIYN; the survey takes advantage of the extremely rapid observing cadence rates possible with WIYN and (especially) DCT. The current status and results are from the first 20+ nights of observing.
  178. Neugent, K., Levesque, E., Massey, P., 2019, AAS, 233, 259.19, Binary Red Supergiants: A New Method for Detecting B-type Companions
    With the exception of a few well-known and studied systems, the binary population of red supergiants (RSGs) remains relatively uncharacterized. Famous systems such as VV Cep, 31 Cyg and zeta Aur contain RSG + B star binaries and here we explore whether B stars are the main type of companion we expect from an evolutionary point of view. Using the Geneva evolutionary models we find that this is indeed the case. However, few such systems are known, and we use model spectra to determine how easy such binaries would be to detect observationally. We find that it should be quite difficult to hide a B-type companion given a reasonable signal-to-noise in the optical / blue portion of the spectrum. We next examine spectra of Magellanic Cloud RSGs and newly acquired spectra of Galactic RSGs looking for new systems and refining our conclusions about what types of stars could be hidden in the spectra. We finally develop a set of photometric criteria that can help select likely binaries in the future without the overhead of large periodic or spectroscopic surveys. We also recently observed spectra of a sample of candidate RSG+B star binaries in M31 and M33, confirming that our photometric criteria can indeed be used to select RSG+B star binaries.
  179. White, R., Schaefer, G., Boyajian, T., et al., (including von Braun, K.), 2019, AAS, 233, 259.41, Stellar Radius Measurements of the Young Debris Disk Host AU Mic
    We present results from our on-going program to directly measure the sizes of nearby young stars using the CHARA Array interferometer. Here we highlight new diameter measurements of AU Mic (GJ 803), an M1 spectral type star that harbors a debris disk and is a member of the Beta Pictoris Moving Group. The star is spatially resolved with an angular diameter of just over 0.7 milli-arcseconds, corresponding to a physical radius of about 0.75 solar radii. We describe our observational strategies for calibrating measurements of this low elevation star (DEC = -31 degrees), and present new high dispersion spectra and high spatial resolution images of the calibrators that aided in this. This size is roughly 60% larger than the average size of similar temperature main sequence stars; it is a bona-fide pre-main sequence star, and the first such low mass star ever spatially resolved. The size measurement is combined with AU Mic's bolometric flux to directly determine its effective temperature for more accurate placement on the HR diagram. The results provide an independent age estimate of the Moving Group, a temporal stamp on the evolutionary state of the debris disk, and offer a benchmark for theories of how low mass stars gravitationally settle toward the main sequence.
  180. Laufman, L., Hunter, D., Oh, S., 2019, AAS, 233, 351.18, Mechanisms for Inducing Star Formation in the Dwarf Irregular Galaxy DDO 133
    Dwarf irregular galaxies are important to study for several reasons. First, they are the most abundant galaxy in the universe; in the Local Group we have more than fifty dwarfs and just three spirals. In addition to being the most common, they are the closest analogue to the building blocks of the early universe and their lack of heavy elements imitates early universe star formation conditions. However, the models say that dwarf irregulars shouldn't be able to continuously form stars; they aren't dense enough to reach the critical density for gravitational instabilities to form and collapse the gas clouds. We present a study of peculiar gas motions and their connection with star formation in the dwarf irregular galaxy DDO 133. Using primarily HI data cubes from the VLA, we build moment maps to identify the motion and location of the gas, and use previously written code to deconvolve these moment maps into bulk and peculiar motions. We identify a stellar bar in DDO 133 with characteristic streaming motions of HI around said bar, likely causing the significant amounts of HI and star formation observed at the ends of the bar. This research was funded by NSF grant 1461200 to Northern Arizona University to support the 2018 Research Experiences for Undergraduates program.
  181. Massey, P., Neugent, K., Morrell, N., et al., 2019, AAS, 233, 353.01, A Modern Search for Wolf-Rayet (WR) Stars in the Magellanic Clouds: A Final Census
    Wolf-Rayet (WR) stars evolved from massive OB stars, where the outer hydrogen-rich layers have been stripped away by some mechanism: stellar winds, close binary companions, episodic mass-loss during a Luminous Blue Variable phase, or all of the above. We have recently carried out a new survey of the Small and Large Magellanic Clouds (SMC, LMC) discovering 15 new WR in the LMC, bringing the total known to 154. We also found 12 Of-type stars, incluing rare Onfp and Of?p stars, and a variety of other interesting emission-lined stars. Most exciting, however, has been our discovery of new class of WRs, which we are calling WN3/O3s. These have the typical emission lines of a high-excitation nitrogen-rich (WN) Wolf-Rayet, but the absorption lines of a hot O-type star. However, they are many magnitudes too faint to be WN3+O3 binaries. Rather, the emission and absorption originate from the same object. Detailed analysis of our Magellan spectra have shown that the physical properties of these stars are similar to normal WNs, but with the presence of more hydrogen and much lower mass-loss rates. About 8% of the LMC's WN-type population is made up of these newly found objects, and so these are not a consequence of some rare and special process. The question then is how did these WN3/O3s evolve? Are they simply a short-lived phase in the normal evolution of WRs, a "missing link" between O-type stars and WRs that occurs only in certain metallicity regimes? Or have they evolved by binary evolution? Drop by our poster and hear what we have to say on the issue! This work was supported by the National Science Foundation through AST-1612874.
  182. Aadland, E., Massey, P., Neugent, K., et al., 2019, AAS, 233, 353.05, Shedding Light on the Isolation of Luminous Blue Variables
    In the traditional view of massive star evolution, luminous blue variables (LBVs) are a transitionary phase between massive O-type stars and Wolf-Rayet stars (WRs). A debate has sprouted over whether this single star evolution is flawed and perhaps a binary evolutionary track describes the LBV phase better. The root of this debate has been the question of isolation (projected angular separation) of LBVs from their nearest neighboring O-type star. LBVs, traditionally, have relatively short lifetimes, and as a result they should not disperse far from their birthplace or be isolated. A recent study found that LBVs have an isolation more similar to that of red supergiants (RSGs) than traditionally thought possible given single star evolution. A similar study, however, found the opposite result. Both of these studies used spectroscopically identified O-type stars, which for the Large Magellanic Cloud is extremely incomplete, and does not necessarily represent the high mass stars we expect to be LBV progenitors in any event. Therefore, we re-examined the question of isolation using photometric criteria to select the highest mass unevolved stars ("bright blue stars" or BBSs) to use as our comparison sample. We find that LBVs are no more isolated than BBSs or WRs, and were able to statistically rule out the possibility of LBVs coming from the same distribution as the RSGs. We also note the number of LBVs in or near OB associations is comparable to the number of BBSs or WRs, and not to that of RSGs. Therefore, we conclude that the isolation of LBVs is consistent with the traditional picture of massive single star evolution. This work was supported by the National Science Foundation through AST-1612874.
  183. Prato, L., Sullivan, K., Lindstrom, K., et al., (including Graham, S.), 2019, AAS, 233, 366.13, Identifying and Characterizing New Spectroscopic Binaries in Orion
    Double-lined, young spectroscopic binaries provide the opportunity for precise measurements of pre-main sequence stellar mass ratios. In conjunction with additional information, such as orbital inclinations based on astrometric photocenter orbits, available in the future from GAIA, very precise stellar component masses may be determined. Mass ratio distributions yield clues to the formation of the closest binaries, a poorly understood problem. Absolute young star masses are important to test and refine the pre-main sequence evolutionary models that are central to the determination of properties such as the initial mass function, secondary star mass function, and star formation history of young clusters. We report on the results of our optical and infrared observations to identify and characterize new spectroscopic binaries in the Orion star forming region. Support for this research was provided in part by NSF award AST-1518081.
  184. Lindstrom, K., Prato, L., Graham, S., et al., (including Nofi, L.), 2019, AAS, 233, 367.04, Binary Stars and their Planet-Forming Disks
    The majority of stars in our Galaxy reside in binary or higher order multiple systems. This can have profound effects on the evolution of the stars and in particular their circumstellar disks and the planet formation therein. In this poster we address several fundamental questions: how do circumstellar disks in binaries evolve, are these disks stable, and are their properties favorable for planet formation? To address these topics, our team is completing a spectroscopic survey of over 100 binary systems in young, nearby star forming regions, including Taurus Auriga, using the Keck II and Discovery Channel Telescopes. Our goal is to analyze these spectra to infer the properties of the stars themselves, as well as their constituent disks. To accomplish this, we generate synthetic spectra with a wide range of effective temperatures, surface gravities, rotational velocities, radial velocities, veiling, and magnetic field strengths for comparison with our target spectra. We present some preliminary results and a discussion of their consequences with respect to the evolution of these systems. This research was supported in part by NSF awards AST-1313399 and AST-1518081 and by NASA Keck KPDA funds.
  185. Hartman, Z., van Belle, G., Lepine, S., et al., (including Clark, C.), 2019, AAS, 233, 418.03, The SUPERWIDE Catalog of Wide Binaries and an Initial Look at the Higher Order Multiplicity of K and M dwarf Wide Binaries
    We present the SUPERWIDE catalog of wide binaries that were identified through a Bayesian analysis of high proper motions stars (m>40 mas/yr) from the Gaia DR2 catalog. Initially identified through an earlier search of the SUPERBLINK high proper motion catalog, these binaries were found by their proximity on the sky, common proper motion and similar distances. Taking those pairs with a probability of being a "true" binary (i.e. gravitationally bound system) greater than 99%, we identify ~22,000 wide binaries with projected physical separations between ~100 AU to ~1 pc. We present initial results of an ongoing speckle survey of these wide binaries devoted to the identification of higher order multiples. Using data collected through the POKEMON M-dwarf multiplicity survey, we have examined ~15 wide binaries to see if they are in fact triple or quadruple systems. With this information and more to come, we intend to determine the higher order multiplicity fraction for K and M dwarf wide binaries as a function of their physical separation in order to provide constraints for the possible formation mechanisms of these wide systems.
  186. Heilman, M., van Belle, G., Clark, J., et al., (including Depinet, J.), 2019, AAS, 233, 462.07, Developing Low-Cost Adaptive Optics Telescopes for Long Baseline Optical Interferometry
    Our research examines the use of adaptive optics (AO) in tandem with low-quality optics to determine if diffraction limited results can be achieved using active corrective optics. The 1m scale of wavefront corrections provided by AO systems are substantially greater than the ~50nm construction specifications of typical telescopes. Thus, this pairing of optics and software could increase image quality while decreasing cost by significantly (~20x) relaxing mechanical requirements. As a baseline, we measured a 6in lab-quality flat with a Zygo interferometer, an instrument built for surface inspection of diffraction-limited optics. To contrast this result, we similarly inspected a low-quality mirror. We found roughly 2 full waves, about 1m, of smoothly varying static wavefront distortion across the ~5in Zygo inspection aperture. Our lab setup consisted of a Thorlabs AO Kit (model 7) with light source, deformable mirror (DM), and Shack-Hartman wavefront sensor (WFS). A 2.5cm beam expanded from a 0.34mW laser diode hit the low-quality mirror, which retroreflected into the AO system and was re-collimated to 5mm to match the sensor diameter of the WFS. Fifteen data sets were collected to find the Peak-to-Valley (PV) and root-mean-square (rms) of the wavefront measured from the low-quality mirror and the reconstructed wavefront corrected by the DM. This second data set was used to calculate the difference between the measured and reconstructed wavefronts. The process was repeated by replacing the low-quality mirror with a lab-quality mirror rated to /20. The PV measurement for the low-quality mirror was 55m with a rms of 12.7m, compared to the lab-quality mirror whose PV was 53m with a rms of 10.8m. The difference between the low-quality mirror's wavefront and the DM reconstructed wavefront was a PV of 0.21m with a rms of 0.04m. The resultant wavefront corrected 80% past it's predicted outcome of 1m. Our results indicate it would be advantageous to use a telescope design that assumes integral AO from the outset; further benefits come from tailoring the telescopes to the narrow set of specifications that emphasize use in a narrow-angle long-baseline optical interferometry system.
  187. Docobo, J., Gomez, J., Campo, P., et al., (including Horch, E.), 2019, MNRAS, 482, 4096, Orbits of 14 binaries based on 2018 SOAR speckle observations
    New data obtained during the 2018 March-April speckle run at the 4.1 m Southern Astrophysical Research (SOAR) telescope located at Cerro Pachon (Chile) allowed us to recalculate the orbits of the following visual binaries: WDS 06478+0020 (STT 157), WDS 07003-2207 (FIN 334Aa,Ab), WDS 07013-0906 (A 671), WDS 10174-5354 (CVN 16Aa,Ab), WDS 12155-3106 (RST 1658), WDS 12572+0818 (FIN 380), WDS 13044-1316 (HU 642), WDS 14243-3838 (RST 1785), WDS 16094-3103 (I 557), WDS 17115-1630 (HU 169), WDS 17119-0151 (LPM 629), WDS 17563 + 0259 (A 2189), WDS 18464-2755 (RST 2073), and WDS 19035-6845 (FIN 357). All but three of them are Southern stars. The recently published Gaia parallaxes were used to calculate the total mass of each of these systems, despite the fact that, in a few cases, only Hipparcos parallaxes were available. For two binaries, A 671 and RST 2073, there are no parallax data. However, in these cases, the masses deduced from the dynamical parallaxes provided relevant information. In addition, we also present the first orbit for each of three systems: HU 642, RST 1785, and RST 2073, using speckle measurements. Finally, using the dynamical parallaxes given by these orbits, we have been able to calculate the luminosity of these systems. Said luminosities allow us to indicate an approximate age for each of the components of the system, situating them within the HR diagram.
  188. Armstrong, J., Jorgensen, A., Mozurkewich, D., et al., (including van Belle, G.), 2019, JAI, 8, 1950012-246, Interferometric Fringe Visibility Null as a Function of Spatial Frequency: A Probe of Stellar Atmospheres
    We introduce an observational tool based on visibility nulls in optical spectro-interferometry fringe data to probe the structure of stellar atmospheres. In a preliminary demonstration, we use both Navy Precision Optical Interferometer (NPOI) data and stellar atmosphere models to show that this tool can be used, for example, to investigate limb darkening.

    Using bootstrapping with either multiple linked baselines or multiple wavelengths in optical and infrared spectro-interferometric observations of stars makes it possible to measure the spatial frequency u0 at which the real part of the fringe visibility Re(V) vanishes. That spatial frequency is determined by u0=B/0, where B is the projected baseline length, and 0 is the wavelength at which the null is observed. Since B changes with the Earths rotation, 0 also changes. If u0 is constant with wavelength, 0 varies in direct proportion to B. Any departure from that proportionality indicates that the brightness distribution across the stellar disk varies with wavelength via variations in limb darkening, in the angular size of the disk, or both.

    In this paper, we introduce the use of variations of u0 with as a means of probing the structure of stellar atmospheres. Using the equivalent uniform disk diameter UD, 0(0), given by UD, 0=1.22/u0(0), as a convenient and intuitive parameterization of u0(0), we demonstrate this concept by using model atmospheres to calculate the brightness distribution for Ophiuchi and to predict UD, 0(0), and then comparing the predictions to coherently averaged data from observations taken with the NPOI.

  189. Mozurkewich, D., Jorgensen, A., van Belle, G., 2019, JAI, 8, 1950005, Coherent Integration in Astronomical Interferometry: Theory and Practice
    Ground-based long-baseline astronomical interferometry operates in a regime where short integration exposures are demanded by working in the presence of a turbulent atmosphere. To reduce piston noise to less than one radian per aperture, these exposure times are on order 10 milliseconds or less in the visible. It has long been recognized that, in the low signal-to-noise ratio (SNR) regime, the visibility SNR is improved by co-adding frames, each rotated by an estimate of its phase. However, implementation of this technique is challenging. Where it is most needed, on low SNR baselines and when combining multiple phases to estimate the phase for a lower SNR baseline, phase errors reduce the amplitude by a large amount and in a way that has proven difficult to calibrate. In this paper, an improved coherent integration algorithm is presented. A parameterized model for the phase as a function of time and wavelength is fit to the entire data set. This framework is used to build a performance model which can be used in two ways. First, it can be used to test the algorithm; by comparing its performance to theory, one can test how well the parameter fitting has worked. Also, when designing future systems, this model provides a simple way to predict performance and compare it to alternative techniques such as hierarchical fringe tracking. This technique has been applied to both simulated and stellar data.
  190. 189 publications and 2621 citations in 2019.

189 publications and 2621 citations total.