@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/107679, title ="Ganymede’s Surface Properties from Millimeter and Infrared Thermal Emission", author = "de Kleer, Katherine and Butler, Bryan", journal = "Planetary Science Journal", volume = "2", number = "1", pages = "Art. No. 5", month = "February", year = "2021", doi = "10.3847/psj/abcbf4", issn = "2632-3338", url = "https://resolver.caltech.edu/CaltechAUTHORS:20210122-151827531", note = "© 2021 The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. \n\nReceived 2020 August 16; revised 2020 November 13; accepted 2020 November 16; published 2021 January 22. \n\nThis work was supported in part by the Heising-Simons Foundation 51 Pegasi b postdoctoral fellowship to K. de Kleer. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2016.1.00691.S, ADS/JAO.ALMA#2018.1.01292.S, ADS/JAO.ALMA#2011.0.00001.CAL. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.", revision_no = "9", abstract = "We present thermal observations of Ganymede from the Atacama Large Millimeter Array (ALMA) in 2016–2019 at a spatial resolution of 300–900 km (0.”1–0.”2 angular resolution) and frequencies of 97.5, 233, and 343.5 GHz (wavelengths of 3, 1.3, and 0.87 mm); the observations collectively covered all Ganymede longitudes. We determine the global thermophysical properties using a thermal model that considers subsurface emission and depth- and temperature-dependent thermophysical and dielectric properties, in combination with a retrieval algorithm. The data are sensitive to emission from the upper ~0.5 m of the surface, and we find a millimeter emissivity of 0.75–0.78 and (sub)surface porosities of 10%–40%, corresponding to effective thermal inertias of 400–800 J m⁻² K⁻¹ s^(−1/2). Combined with past infrared results, as well as modeling presented here of a previously unpublished night-time infrared observation from Galileo's photopolarimeter–radiometer instrument, the multiwavelength constraints are consistent with a compaction profile whereby the porosity drops from ~85% at the surface to 10⁺³⁰₋₁₀% at depth over a compaction length scale of tens of centimeters. We present maps of temperature residuals from the best-fit global models, which indicate localized variations in thermal surface properties at some (but not all) dark terrains and at impact craters, which appear 5–8 K colder than the model. Equatorial regions are warmer than predicted by the model, in particular near the centers of the leading and trailing hemispheres, while the midlatitudes (~30°–60°) are generally colder than predicted; these trends are suggestive of an exogenic origin.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/103911, title ="An attempt to detect transient changes in Io’s SO₂ and NaCl atmosphere", author = "Roth, Lorenz and Boissier, Jérémie", journal = "Icarus", volume = "350", pages = "Art. No. 113925", month = "November", year = "2020", doi = "10.1016/j.icarus.2020.113925", issn = "0019-1035", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200615-092222832", note = "© 2020 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). \n\nReceived 24 March 2020, Revised 4 June 2020, Accepted 10 June 2020, Available online 12 June 2020. \n\nL. R. appreciates the support from the Swedish National Space Agency (SNSA) through grant 154/17 and the Swedish Research Council (VR) through grant 2017-04897. A. S.-M., P. S. and S. T. (Cologne) have been supported via Collaborative Research Centre 956, funded by the Deutsche Forschungsgemeinschaft, Germany (DFG; project ID 184018867) and DFG, Germany SCHL 341/15-1 (“Cologne Center for Terahertz Spectroscopy”).", revision_no = "17", abstract = "Io’s atmosphere is predominately SO₂ that is sustained by a combination of volcanic outgassing and sublimation. The loss from the atmosphere is the main mass source for Jupiter’s large magnetosphere. Numerous previous studies attributed various transient phenomena in Io’s environment and Jupiter’s magnetosphere to a sudden change in the mass loss from the atmosphere supposedly triggered by a change in volcanic activity. Since the gas in volcanic plumes does not escape directly, such causal correlation would require a transient volcano-induced change in atmospheric abundance, which has never been observed so far. \n\nHere we report four observations of atmospheric SO₂ and NaCl from the same hemisphere of Io, obtained with the IRAM NOEMA interferometer on 11 December 2016, 14 March, 6 and 29 April 2017. These observations are compared to measurements of volcanic hot spots and Io’s neutral and plasma environment. We find a stable NaCl column density in Io’s atmosphere on the four dates. The SO₂ column density derived for December 2016 is about 30% lower compared to the SO₂ column density found in the period of March to April 2017. This increase in SO₂ from December 2016 to March 2017 might be related to increasing volcanic activity observed at several sites in spring 2017, but the stability of the volcanic trace gas NaCl and resulting decrease in NaCl/SO₂ ratio do not support this interpretation. Observed dimmings in both the sulfur ion torus and Na neutral cloud suggest rather a decrease in mass loading in the period of increasing SO₂ abundance. The dimming Na brightness and stable atmospheric NaCl furthermore dispute an earlier suggested positive correlation of the sodium cloud and the hot spot activity at Loki Patara, which considerably increased in this period. The environment of Io overall appears to be in a rather quiescent state, preventing further conclusions. Only Jupiter’s aurora morphology underwent several short-term changes, which are apparently unrelated to Io’s quiescent environment or the relatively stable atmosphere.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/104475, title ="High Spatial and Spectral Resolution Observations of the Forbidden 1.707 μm Rovibronic SO Emissions on Io: Evidence for Widespread Stealth Volcanism", author = "de Pater, Imke and de Kleer, Katherine", journal = "Planetary Science Journal", volume = "1", number = "2", pages = "Art. No. 29", month = "September", year = "2020", doi = "10.3847/PSJ/ab9eb1", issn = "2632-3338", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200721-101801680", note = "© 2020 The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. \n\nReceived 2019 November 24; revised 2020 June 17; accepted 2020 June 18; published 2020 July 20. \n\nWe thank Darrell Strobel for fruitful discussions regarding the interpretation of our observations. We appreciate Peter Bernath's communication pointing out his recent paper on new line lists of SO. We thank Emmanuel Lellouch and an anonymous referee for careful and detailed reviews of our manuscript, which helped improve the paper substantially. We further thank Edward Molter for reducing the NIRC2 data from 2019 April 15. Our research was supported by the National Science Foundation, NSF grant AST-1313485 to UC Berkeley. The data presented in this paper were obtained at the W.M. Keck Observatory. The Keck Telescopes are operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations of Ionian volcanoes from this Hawaiian volcano.", revision_no = "7", abstract = "We present observations obtained with the 10 m Keck telescopes of the forbidden SO a¹Δ → X³Σ⁻ rovibronic transition at 1.707 μm on Io while in eclipse. We show its spatial distribution at a resolution of ~0.”12 and a spectral resolution of R ~ 2500, as well as disk-integrated spectra at a high spectral resolution (R ~ 15,000). Both the spatial distribution and the spectral shape of the SO emission band vary considerably across Io and over time. In some cases the SO emissions either in the core or the wings of the emission band can be identified with volcanoes, but the largest areas of SO emissions usually do not coincide with known volcanoes. We suggest that the emissions are caused by a large number of stealth plumes, produced through the interaction of silicate melts with superheated SO₂ vapor at depth. The spectra, in particular the elevated wing of the emission band near 1.69 μm, and their spatial distribution strongly suggest the presence of nonlocal thermodynamic equilibrium processes in addition to the direct ejection of excited SO from the (stealth and other) volcanic vents.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/99353, title ="Does Io Have a Magma Ocean?", author = "McEwen, Alfred S. and de Kleer, Katherine", journal = "EoS - Earth & Space Science News", month = "October", year = "2019", doi = "10.1029/2019EO135617", issn = "2324-9250", url = "https://resolver.caltech.edu/CaltechAUTHORS:20191018-092951305", note = "© 2019. The authors. CC BY-NC-ND 3.0.", revision_no = "9", abstract = "Future space missions will further our knowledge of tidal heating and orbital resonances, processes thought to create spectacular volcanism and oceans of magma or water on other worlds.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/96628, title ="Io’s Volcanic Activity from Time Domain Adaptive Optics Observations: 2013–2018", author = "de Kleer, Katherine and de Pater, Imke", journal = "Astronomical Journal", volume = "158", number = "1", pages = "Art. No. 29", month = "July", year = "2019", doi = "10.3847/1538-3881/ab2380", issn = "1538-3881", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190621-131307341", note = "© 2019 The American Astronomical Society. \n\nReceived 2019 January 26; revised 2019 May 13; accepted 2019 May 14; published 2019 June 21. \n\nK.d.K. is supported by the Heising-Simons Foundation through a 51 Pegasi b postdoctoral fellowship, and this research was partially supported by the National Science Foundation grant AST-1313485 to UC Berkeley and a NASA Keck PI Data Award, administered by the NASA Exoplanet Science Institute. We are grateful to Roy and Frances Simperman for their support of the Keck Visiting Scholars program, which enabled K.d.K., E.M., and C.A. to develop the Keck twilight program through which some of the data presented here were obtained. We thank G. Puniwai for acquiring several of the Keck observations. We thank P. Capak, J. Cohen, N. Hernitschek, D. Masters, and S.A. Stanford of the the Complete Calibration of the Color-Redshift Relation (C3R2; Masters et al. 2017) NASA Keck Key Strategic Mission Support survey team for providing twilight observations on the nights of UT 2017 December 11–13. The work of D.S. and A.G.D. was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. Much of the data presented herein were obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), Ministério da Ciência, Tecnologia e Inovação (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. Some of the data was obtained at the W. M. Keck Observatory from telescope time allocated to the National Aeronautics and Space Administration through the agency's scientific partnership with the California Institute of Technology and the University of California. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.", revision_no = "10", abstract = "We present measurements of the near-infrared brightness of Io's hot spots derived from 2 to 5 μm imaging with adaptive optics on the Keck and Gemini N telescopes. The data were obtained on 271 nights between 2013 August and the end of 2018, and include nearly 1000 detections of over 75 unique hot spots. The 100 observations obtained between 2013 and 2015 have been previously published in de Kleer & de Pater the observations since the start of 2016 are presented here for the first time, and the analysis is updated to include the full five-year data set. These data provide insight into the global properties of Io's volcanism. Several new hot spots and bright eruptions have been detected, and the preference for bright eruptions to occur on Io's trailing hemisphere noted in the 2013–2015 data is strengthened by the larger data set and remains unexplained. The program overlapped in time with Sprint-A/EXCEED and Juno observations of the Jovian system, and correlations with transient phenomena seen in other components of the system have the potential to inform our understanding of the impact of Io's volcanism on Jupiter and its neutral/plasma environment.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/97912, title ="Variability in Io's Volcanism on Timescales of Periodic Orbital Changes", author = "de Kleer, Katherine and Nimmo, Francis", journal = "Geophysical Research Letters", volume = "46", number = "12", pages = "6327-6332", month = "June", year = "2019", doi = "10.1029/2019GL082691", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190815-091534549", note = "© 2019 American Geophysical Union. \n\nReceived 6 MAR 2019; Accepted 5 MAY 2019; Accepted article online 8 MAY 2019; Published online 24 JUN 2019. \n\nThe authors are grateful to Ryan Park for providing Horizons data products, Michael E. Brown for statistics feedback, and Emily Brodsky for advice on poroelastic flow. K. d. K. is supported by the Heising‐Simons Foundation through a 51 Pegasi b postdoctoral fellowship. The authors declare no financial conflicts of interest. The data supporting the conclusions can be found in the following locations: (a) for observations prior to 2001: Rathbun et al. (2002, Figure 1), Rathbun and Spencer (2006, Figure 1), Rathbun and Spencer (2010, Figure 2); (b) for Galileo NIMS observations: Davies et al. (2012); and (c) for adaptive optics observations from 2001 to 2018: Data Set S1, which compiles data from de Pater et al. (2017), de Kleer and de Pater (2016), and de Kleer et al. (2019).", revision_no = "16", abstract = "The widespread volcanism on the Jovian moon Io is powered by tidal heating, yet we lack a deep understanding of how this distinctive heating process affects the locations, timing, or intensities of Io's eruptions. We show that the quasiperiodic behavior of the volcano Loki Patera in 1987–2018 matches the timescales for the evolution of Io's eccentricity and semimajor axis (~480 and ~460 days). If this orbital forcing is driving Loki Patera's variability, a low‐pass geophysical filter such as poroelastic flow, or a resonant amplification of Io's wobble, could account for the importance of these long‐period orbital variations despite their small amplitudes. The peak volcanic response is predicted to roughly coincide with Io's maximum eccentricity, consistent with the observations. High‐cadence observations over the next several years have the potential to conclusively discriminate between orbital versus geophysical control of Loki Patera's variability.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/91268, title ="Analysis of Neptune’s 2017 Bright Equatorial Storm", author = "Molter, Edward and de Pater, Imke", journal = "Icarus", volume = "321", pages = "324-345", month = "March", year = "2019", doi = "10.1016/j.icarus.2018.11.018", issn = "0019-1035", url = "https://resolver.caltech.edu/CaltechAUTHORS:20181128-090728975", note = "© 2018 Published by Elsevier Inc. \n\nReceived 2 July 2018, Revised 5 November 2018, Accepted 19 November 2018, Available online 28 November 2018. \n\nSome of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. \n\nThe authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. \n\nPartial support for this work was also provided by the Keck Visiting Scholar Program at W.M. Keck Observatory. \n\nPortions of this research are based on observations made with the NASA/ESA Hubble Space Telescope, (OPAL program GO14756) obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5–26555. \nResearch at Lick Observatory is partially supported by a generous gift from Google. \n\nThis work has been supported in part by the National Science Foundation, NSF Grant AST-1615004 to UC Berkeley. \n\nR. H. and A.S-L. were supported by the Spanish MINECO project AYA2015-65041-P with FEDER, UE support and Grupos Gobierno Vasco IT-765-13. \n\nPortions of this work were performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. \n\nWe thank the referees, Amy Simon and one anonymous person, for their insightful comments, which substantially improved the manuscript. \n\nWe thank Conor McPartland as well as all of the Keck Observing Assistants for executing our volunteer observing program during their observing time at Keck Observatory. \n\nWe thank Geoff Chen, Ian Crossfield, Donald Gavel, and Robert de Rosa for executing our volunteer observing program during their observing time at Lick Observatory.", revision_no = "27", abstract = "We report the discovery of a large (\u202f∼\u202f8500\u202fkm diameter) infrared-bright storm at Neptune’s equator in June 2017. We tracked the storm over a period of 7 months with high-cadence infrared snapshot imaging, carried out on 14 nights at the 10\u202fm Keck II telescope and 17 nights at the Shane 120 inch reflector at Lick Observatory. The cloud feature was larger and more persistent than any equatorial clouds seen before on Neptune, remaining intermittently active from at least 10 June to 31 December 2017. Our Keck and Lick observations were augmented by very high-cadence images from the amateur community, which permitted the determination of accurate drift rates for the cloud feature. Its zonal drift speed was variable from 10 June to at least 25 July, but remained a constant 237.4\u202f±\u202f0.2 m s^(−1) from 30 September until at least 15 November. The pressure of the cloud top was determined from radiative transfer calculations to be 0.3-0.6\u202fbar; this value remained constant over the course of the observations. Multiple cloud break-up events, in which a bright cloud band wrapped around Neptune’s equator, were observed over the course of our observations. No “dark spot” vortices were seen near the equator in HST imaging on 6 and 7 October. The size and pressure of the storm are consistent with moist convection or a planetary-scale wave as the energy source of convective upwelling, but more modeling is required to determine the driver of this equatorial disturbance as well as the triggers for and dynamics of the observed cloud break-up events.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87933, title ="Emission from Volcanic SO Gas on Io at High Spectral Resolution", author = "de Kleer, Katherine and de Pater, Imke", journal = "Icarus", volume = "317", pages = "104-120", month = "January", year = "2019", doi = "10.1016/j.icarus.2018.07.012", issn = "0019-1035", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180717-143037489", note = "© 2018 Elsevier Inc. \n\nReceived 10 February 2018, Revised 12 June 2018, Accepted 13 July 2018, Available online 17 July 2018. \n\nSupplementary material associated with this article can be found, in the online version, at 10.1016/j.combustflame.2015.11.022. \n\nK. de Kleer is supported by the Heising-Simons Foundation 51 Pegasi b postdoctoral fellowship; this work was also partially supported by the National Science Foundation grant AST-1313485 to UC Berkeley. This work made use of the JPL Solar System Dynamics high-precision ephemerides through the HORIZONS system. Data were obtained with the W.M. Keck Observatory, which is operated by the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. Data were also obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), and Ministério da Ciência, Tecnologia e Inovação (Brazil). The authors extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. Without their generous hospitality, none of the observations presented would have been possible.", revision_no = "25", abstract = "Jupiter’s moon Io hosts a dynamic atmosphere that is continually stripped off and replenished through frost sublimation and volcanic outgassing. We observed an emission band at 1.707\u202fµm thought to be produced by hot SO molecules directly ejected from a volcanic vent; the observations were made with the NIRSPEC instrument on the Keck II telescope while Io was in eclipse by Jupiter on three nights in 2012–2016, and included two observations with 10\u202f×\u202fhigher spectral resolution than all prior observations of this band. These high-resolution spectra permit more complex and realistic modeling, and reveal a contribution to the SO emission from gas reservoirs at both high and low rotational temperatures. The scenario preferred by de Pater et al. (2002) for the source of the SO gas – direct volcanic emission of SO in the excited state – is consistent with these two temperature components if the local gas density is high enough that rotational energy can be lost collisionally before the excited electronic state spontaneously decays. Under this scenario, the required bulk atmospheric gas density and surface pressure are n\u202f∼\u202f10^(11) cm^(−3) and 1–3 nbar, consistent with observations and modeling of Io’s dayside atmosphere at altitudes below 10\u202fkm (Lellouch et al., 2007; Walker et al., 2010). These densities and pressures would be too high for the nightside density if the atmospheric density drops by an order of magnitude or more at night (as predicted by sublimation-supported models), but recent results have shown a drop in SO_2 gas density of only a factor of 5 \u202f±\u202f 2 (Tsang et al., 2016). While our observations taken immediately post-ingress and pre-egress (on different dates) prefer models with only a factor of 1.5 change in gas density, a factor of 5 change is still well within uncertainties. In addition, our derived gas densities are for the total bulk atmosphere, while Tsang et al. (2016) specifically measured SO_2. The low-temperature gas component is warmer for observations in the first 20 min of eclipse (in Dec 2015) than after Io had been in shadow for 1.5 h (in May 2016), suggesting cooling of the atmosphere during eclipse. However, individual spectra during the first \u202f∼\u202f30 min of eclipse do not show a systematic cooling, indicating that such a cooling would have to take place on a longer timescale than the \u202f∼\u202f10 min for cooling of the surface (Tsang et al., 2016). Excess emission is consistently observed at 1.69\u202fµm, which cannot be matched by two-temperature gas models but can be matched by models that over-populate high rotational states. However, a detailed assessment of disequilibrium conditions will require high-resolution spectra that cover both the center of the band and the wing at 1.69\u202fµm. Finally, a comparison of the total band strengths observed across eight dates from 1999 to 2016 reveals no significant dependence on thermal hot spot activity (including Loki Patera), on the time since Io has been in shadow, nor on the phase of Io’s orbit at the time of observation.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/92550, title ="Europa’s Optical Aurora: Update from Four New Hubble Eclipse Observations", author = "de Kleer, Katherine and Brown, Michael E.", journal = "Research Notes of the AAS", volume = "3", number = "1", pages = "Art. No. 27", month = "January", year = "2019", doi = "10.3847/2515-5172/ab0289", issn = "2515-5172", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190131-140437698", note = "© 2019. The American Astronomical Society. \n\nReceived 2019 January 27. Accepted 2019 January 28. Published 2019 January 31. \n\nSupport for this work was provided by NASA through grant number HST-GO-15425.002-A from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555. This work was based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. K. de Kleer is supported by a Heising-Simons Foundation 51 Pegasi b postdoctoral fellowship.", revision_no = "8", abstract = "Atomic emissions from the tenuous atmosphere of Jupiter's moon Europa provide information on the composition, column density, and variability of gas species, which inform our understanding of the atmosphere's origins. The strength and ratios of the UV and optical oxygen emission lines indicate that Europa's atmosphere is composed primarily of O_2 and has a column density of ~1–15 × 10^(14) cm^(−2) (Hall et al. 1998; Roth et al. 2014, 2016; de Kleer & Brown 2018). The auroral emissions show variability on timescales from minutes to days, some of which can be attributed to Europa's position relative to Jupiter's plasma sheet (Roth et al. 2016; de Kleer & Brown 2018). The atmosphere is sourced from Europa's surface, from which material is liberated via sputtering and/or thermal processes (Johnson 1990; Oza et al. 2018).", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/90038, title ="Europa's Optical Aurora", author = "de Kleer, Katherine and Brown, Michael E.", journal = "Astronomical Journal", volume = "156", number = "4", pages = "Art. No. 167", month = "October", year = "2018", doi = "10.3847/1538-3881/aadae8", issn = "1538-3881", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180927-124355176", note = "© 2018 The American Astronomical Society. \n\nReceived 2018 June 22; revised 2018 August 1; accepted 2018 August 7; published 2018 September 27. \n\nThe authors are grateful to Samantha Trumbo for assistance in obtaining the Keck data. K.dK. is supported by a Heising-Simons Foundation 51 Pegasi b postdoctoral fellowship. Support for this work was also provided by NASA through grant No. HST-GO-15425.002-A from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555. This work was based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This work made use of the JPL Solar System Dynamics high-precision ephemerides through the HORIZONS system.", revision_no = "9", abstract = "Auroral emissions provide opportunities to study the tenuous atmospheres of solar system satellites, revealing the presence and abundance of molecular and atomic species as well as their spatial and temporal variability. Far-UV aurorae have been used for decades to study the atmospheres of the Galilean satellites. Here we present the first detection of Europa's visible-wavelength atomic oxygen aurora at 6300/6364 Å arising from the metastable O(^1D) state, observed with the Keck I and Hubble Space Telescope while Europa was in eclipse by Jupiter on six occasions in 2018 February–April. The disk-integrated O(^1D) brightness varies from <500 R up to more than 2 kR between dates, a factor of 15 higher than the O I 1356 Å brightness on average. The ratio of emission at 6300/5577 Å is diagnostic of the parent molecule; the 5577 Å emission was not detected in our data set, which favors O2 as the dominant atmospheric constituent and rules out an O/O_2 mixing ratio above 0.35. For an O_2 atmosphere and typical plasma conditions at Europa's orbit, the measured surface brightness range corresponds to column densities of (1–9) × 10^(14) cm^(−2).", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/86237, title ="Variability and geologic associations of volcanic activity in 2001-2016", author = "Cantrall, Clayton and de Kleer, Katherine", journal = "Icarus", volume = "312", pages = "267-294", month = "September", year = "2018", doi = "10.1016/j.icarus.2018.04.007", issn = "0019-1035", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180507-091152096", note = "© 2018 Published by Elsevier Inc. \n\nReceived 8 July 2017, Revised 11 March 2018, Accepted 10 April 2018, Available online 5 May 2018. \n\nThe data presented in this paper were obtained at the W.M. Keck Observatories. The Keck Telescopes are operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. Our research was supported by the National Science Foundation, NSF grant AST-1313485 to UC Berkeley. Ashley Davies thanks also the NASA Outer Planets Research and Planetary Geology and Geophysics Programs for support. The authors recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations of Ionian volcanoes from this Hawaiian volcano.", revision_no = "19", abstract = "Since the end of the Galileo epoch, ground-based observations have been crucial for the continued monitoring and characterization of volcanic activity on Jupiter’s moon, Io. We compile and analyze observations from the Keck and Gemini North telescopes between 2001 and 2016, including new and published observations from 2003, 2004, 2005, 2007, 2008, 2009, 2011, 2012, 2013, and 2016. A total of 88 distinct hot spot sites were detected over the 15-year period, 82 of which were detected multiple times, and 24 of which were not detected by Galileo at thermal infrared wavelengths (1–5\u202fµm). A variety of analytical methods are utilized to investigate the detections of active volcanism as a surface expression of interior heating. Geologic associations of hot spots, including patera type, lava flow type, and proximity to mountainous regions, are made using the USGS-published global geologic map of Io (Williams, 2011). We also provide a summary of outburst-scale events, along with the slightly less bright but more frequent, mini-outbursts described by de Kleer and de Pater (2016a).\n\nWe investigate the spatial distribution of volcanic activity on Io using nearest neighbor, mean pairwise spacing, and mean latitude statistics with various classification schemes. The analysis confirms previous findings in that the heat dissipation appears to be primarily concentrated in the asthenosphere resulting in a high time-averaged surface heat flux at low latitudes. Our observations show significant spatial deviations do exist from the asthenosphere heat dissipation model while also suggesting a deeper source of magma ascent to be present as well, supporting conclusions from previous analyses of primarily spacecraft data (Veeder et al., 2012; Hamilton, 2013; Davies et al., 2015). From a temporal perspective, there are signs of significant variations in the distribution of global heat flux, as volcanoes undetected, and probably dormant, during the Galileo encounters subsequently erupted and remained active during our observations. We also use the on 3.8-µm radiant intensity timelines of individual hot spots, along with the distribution of extensive lava fields in relation to detected activity, as a means to investigate possible connections between hot spots and short timescale, spatio-temporal variations in the global heat flux distribution. We conclude that while the global heat flux distribution remains relatively constant over decadal timescales, there is evidence that significant deviations do occur potentially as a result of mountain forming processes or triggering mechanisms between eruptions.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94918, title ="The triaxial ellipsoid size, density, and rotational pole of asteroid (16) Psyche from Keck and Gemini AO observations 2004–2015", author = "Drummond, Jack D. and Merline, William J.", journal = "Icarus", volume = "305", pages = "174-185", month = "May", year = "2018", doi = "10.1016/j.icarus.2018.01.010", issn = "0019-1035", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190424-103200084", note = "© 2018 Published by Elsevier. \n\nReceived 24 July 2017, Revised 30 December 2017, Accepted 10 January 2018, Available online 11 January 2018. \n\nSome of the observations were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. \n\nSome of the observations were obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnologa e Innovacin Productiva (Argentina), and Ministrio da Ciłncia, Tecnologia e Inovao (Brazil). \n\nThe authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. \n\nThis research made use of NASA’s Astrophysics Data System and JPL’s Horizons ephemerides tool. \n\nWe thank two anonymous referees for their helpful reviews.", revision_no = "12", abstract = "We analyze a comprehensive set of our adaptive optics (AO) images taken at the 10\u202fm W. M. Keck telescope and the 8\u202fm Gemini telescope to derive values for the size, shape, and rotational pole of asteroid (16) Psyche. Our fit of a large number of AO images, spanning 14 years and covering a range of viewing geometries, allows a well-constrained model that yields small uncertainties in all measured and derived parameters, including triaxial ellipsoid dimensions, rotational pole, volume, and density. We find a best fit set of triaxial ellipsoid diameters of (a,b,c) = (274\u202f±\u202f9, 231\u202f±\u202f7, 176\u202f±\u202f7) km, with an average diameter of 223\u202f±\u202f7\u202fkm. Continuing the literature review of Carry (2012), we find a new mass for Psyche of 2.43\u202f±\u202f0.35\u202f×\u202f1019 kg that, with the volume from our size, leads to a density estimate 4.16\u202f±\u202f0.64\u202fg/cm3. The largest contribution to the uncertainty in the density, however, still comes from the uncertainty in the mass, not our volume. Psyche’s M classification, combined with its high radar albedo, suggests at least a surface metallic composition. If Psyche is composed of pure nickel-iron, the density we derive implies a macro-porosity of 47%, suggesting that it may be an exposed, disrupted, and reassembled core of a Vesta-like planetesimal. The rotational pole position (critical for planning spacecraft mission operations) that we find is consistent with others, but with a reduced uncertainty: [RA;Dec]=[32°;+5°] or Ecliptic [λ; δ]=[32°;-8°] with an uncertainty radius of 3°. Our results provide independent measurements of fundamental parameters for this M-type asteroid, and demonstrate that the parameters are well determined by all techniques, including setting the prime meridian over the longest principal axis. The 5.00 year orbital period of Psyche produces only four distinct opposition geometries, suggesting that observations before the arrival of Psyche Mission in 2030 should perhaps emphasize observations away from opposition, although the penalty then would be that the asteroid will be fainter and further than at opposition.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94916, title ="Discovery of a Powerful, Transient, Explosive Thermal Event at Marduk Fluctus, Io, in Galileo\n NIMS Data", author = "Davies, A. G. and Davies, R. L.", journal = "Geophysical Research Letters", volume = "45", number = "7", pages = "2926-2933", month = "April", year = "2018", doi = "10.1002/2018gl077477", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190424-103159776", note = "© 2018. American Geophysical Union. \n\nReceived 6 FEB 2018. Accepted 9 MAR 2018. Accepted article online 14 MAR 2018. Published online 6 APR 2018. \n\nThis work was performed at the Jet Propulsion Laboratory‐California Institute of Technology, under contract to NASA. We thank A.S. McEwen and D.A. Williams for their reviews. A.G.D. thanks the NASA Outer Planets Research and Planetary Geology and Geophysics Programs for past support under awards NNN13D466T and NMO710830. The research was partially supported by the National Science Foundation, NSF grant AST‐1313485 to UC Berkeley. L.W. thanks the Leverhulme Trust for an Emeritus Fellowship. NIMS data are available from the NASA Planetary Data System. © Caltech 2018.", revision_no = "14", abstract = "Analysis of Galileo Near‐Infrared Mapping Spectrometer observations of Marduk Fluctus, a volcano on the Jovian moon Io, reveals a style of volcanic activity not previously seen there—a powerful thermal event lasting only a few minutes in 1996. The thermal emission rapidly fades, suggesting extremely rapid cooling of small clasts. The duration and evolution of the explosive eruption are akin to what might be expected from a strombolian or vulcanian explosion. The presence of such events provides an additional volcanic process that can be imaged by future missions with the intent of determining lava composition from eruption temperature, an important constraint on the internal composition of Io. These data promise to be of particular use in understanding the mechanics of explosive volcanic processes on Io.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94917, title ="A New Dark Vortex on Neptune", author = "Wong, Michael H. and Tollefson, Joshua", journal = "Astronomical Journal", volume = "155", number = "3", pages = "Art. No. 117", month = "March", year = "2018", doi = "10.3847/1538-3881/aaa6d6", issn = "1538-3881", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190424-103159951", note = "© 2018. The American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. \n\nReceived 2017 November 21; revised 2017 December 22; accepted 2017 December 29; published 2018 February 15. \n\nBased on observations associated with programs GO-13937, GO-14044, GO-14334, GO-14492, and GO-14756, with support provided by NASA through grants from the Space Telescope Science Institute (operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555). Data were obtained from the Data Archive at the Space Telescope Science Institute. Support was provided by the National Science Foundation through grant AST-1615004 and by the NASA Earth and Space Science Fellowship through grant NNX16AP12H to I.dP. and J.T., and by the Alfred P. Sloan Foundation and the National Science Foundation through grant AST-1712014 to C.B. We acknowledge support from grants AYA2015-65041-P (MINECO/FEDER, UE), Grupos Gobierno Vasco IT-765-13, and UPV/EHU UFI11/55 to A.S.L. and R.H. \n\nWe thank an anonymous reviewer for their quick and constructive review. \n\nFacility: HST(WFC3). - \n\nSoftware: Astroconda, IDL, L.A.Cosmic, WinJUPOS, JPL Horizons Ephemerides.", revision_no = "12", abstract = "An outburst of cloud activity on Neptune in 2015 led to speculation about whether the clouds were convective in nature, a wave phenomenon, or bright companions to an unseen dark vortex (similar to the Great Dark Spot studied in detail by Voyager 2). The Hubble Space Telescope (HST) finally answered this question by discovering a new dark vortex at 45 degrees south planetographic latitude, named SDS-2015 for \"southern dark spot discovered in 2015.\" SDS-2015 is only the fifth dark vortex ever seen on Neptune. In this paper, we report on imaging of SDS-2015 using HST's Wide Field Camera 3 across four epochs: 2015 September, 2016 May, 2016 October, and 2017 October. We find that the size of SDS-2015 did not exceed 20 degrees of longitude, more than a factor of two smaller than the Voyager dark spots, but only slightly smaller than previous northern-hemisphere dark spots. A slow (1.7–2.5 deg/year) poleward drift was observed for the vortex. Properties of SDS-2015 and its surroundings suggest that the meridional wind shear may be twice as strong at the deep level of the vortex as it is at the level of cloud-tracked winds. Over the 2015–2017 period, the dark spot's contrast weakened from about -7% to about -3%, while companion clouds shifted from offset to centered, a similar evolution to some historical dark spots. The properties and evolution of SDS-2015 highlight the diversity of Neptune's dark spots and the need for faster cadence dark spot observations in the future.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94923, title ="Three decades of Loki Patera observations", author = "de Pater, Imke and de Kleer, Katherine", journal = "Icarus", volume = "297", pages = "265-281", month = "November", year = "2017", doi = "10.1016/j.icarus.2017.03.016", issn = "0019-1035", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190424-103200555", note = "© 2017 Elsevier. \n\nReceived 28 November 2016, Revised 11 March 2017, Accepted 16 March 2017, Available online 21 March 2017. \n\nThe data presented in this paper were obtained at the W.M. Keck Observatories. The Keck Telescopes are operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. Our research was partially supported by the National Science Foundation, NSF grant AST-1313485 to UC Berkeley. Ashley Davies thanks the NASA Outer Planets Research and Planetary Geology and Geophysics Programs for support. The authors recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations of Ionian volcanoes from this Hawaiian volcano.", revision_no = "10", abstract = "We present observations of Io's Loki Patera taken with the 10-m Keck telescopes between 1998 and 2016. Adding these data to those published by Rathbun and Spencer (2006) and the Gemini data of de Kleer and de Pater (2016a, 2017) results in a database of 3.5–3.8 µm emission from Loki Patera over almost 3 decades. Data presented here contain adaptive optics (AO) observations of Io's sunlit hemisphere at wavelengths between 1.6 and 5 µm, AO observations of Io in eclipse at 2–5 µm, and non-AO observations of Io in eclipse at 1.6–12 µm. The non-AO data were taken in September of 1999, during the early phase of a brightening event that was documented by Howell et al. (2001). Dual-component Io Flow model (IFM) fits to our 1999 observations show a mostly cool lava crust over almost the entire patera floor, with a relatively small hotter component making up less than 1% of the total area, consistent with previous observations. The 30-year timeline of Loki Patera revealed that, after an apparent cessation of, or change in, brightening events in 2002, Loki Patera became active again in 2009. The more recent activity may have a slightly shorter periodicity than observed by Rathbun et al. (2002), and the direction of flow propagation appears to have reversed. Since 2009 the flow direction is in the clockwise direction, starting in the north or north-east corner and propagating along the patera towards the south-west. During the Galileo era the propagation was in the counter-clockwise direction, starting in the south-west and propagating towards the east. Both the 30-year timeline and the 1.6–12 µm spectrum that was obtained during the brightening event in 1999 agree well with Matson et al.’s (2006) overturning lava lake model, as modified by de Kleer and de Pater (2017).", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/96300, title ="Neptune long-lived atmospheric features in 2013–2015 from small (28-cm) to large (10-m) telescopes", author = "Hueso, R. and de Pater, I.", journal = "Icarus", volume = "295", pages = "89-109", month = "October", year = "2017", doi = "10.1016/j.icarus.2017.06.009", issn = "0019-1035", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190611-141527333", note = "© 2017 Elsevier Inc. \n\nReceived 8 November 2016, Revised 15 May 2017, Accepted 5 June 2017, Available online 7 June 2017. \n\nWe thank two anonymous referees from their constructive comments that improved the contents of this paper. We are very grateful to Grischa Hahn for his update on the WinJupos software incorporating the ephemeris of Triton that allowed the measurement of amateur images of Neptune. We are also grateful to many amateur observers that observed Neptune intensively over 2013 to 2015 providing data for this research. We are also thankful to P. Irwin for giving permission to use his VLT/SINFONI observations of Neptune. Observations for this research were obtained at the following observatories: Pic du Midi in France, Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, Spain, the Lick Observatory and Palomar Observatory in California and the W.M. Keck Observatory in Hawaii. The Centro Astronómico Hispano Alemán (CAHA) at Calar Alto is operated jointly by the Max Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC). The Robo-AO system was developed by collaborating partner institutions, the California Institute of Technology and the Inter-University Centre for Astronomy and Astrophysics, and with the support of the National Science Foundation under grant Nos. AST-0906060, AST-0960343, AST-0908575, AST-1207891 and AST-1615004, the Mt. Cuba Astronomical Foundation, and by a gift from Samuel Oschin. Research at Lick Observatory is partially supported by a generous gift from Google. The W.M. Keck Observatory is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Keck Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Additional observations were acquired by the Hubble Space Telescope (Programs GO 13937, 14044). Portions of this work were performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. C.B. acknowledges support from the Alfred P. Sloan Foundation. This work was supported by the Spanish MINECO project AYA2015-65041-P (MINECO/FEDER, UE), Grupos Gobierno Vasco IT-765-13, UPV/EHU UFI11/55 and ‘Infraestructura’ grants from Gobierno Vasco and UPV/EHU.", revision_no = "10", abstract = "Since 2013, observations of Neptune with small telescopes (28–50 cm) have resulted in several detections of long-lived bright atmospheric features that have also been observed by large telescopes such as Keck II or Hubble. The combination of both types of images allows the study of the long-term evolution of major cloud systems in the planet. In 2013 and 2014 two bright features were present on the planet at southern mid-latitudes. These may have merged in late 2014, possibly leading to the formation of a single bright feature observed during 2015 at the same latitude. This cloud system was first observed in January 2015 and nearly continuously from July to December 2015 in observations with telescopes in the 2-10-m class and in images from amateur astronomers. These images show the bright spot as a compact feature at −40.1 ± 1.6° planetographic latitude well resolved from a nearby bright zonal band that extended from −42° to −20°. The size of this system depends on wavelength and varies from a longitudinal extension of 8000 ± 900 km and latitudinal extension of 6500 ± 900 km in Keck II images in H and Ks bands to 5100 ± 1400 km in longitude and 4500 ± 1400 km in latitude in HST images in 657 nm. Over July to September 2015 the structure drifted westward in longitude at a rate of 24.48 ± 0.03°/day or −94 ± 3 m/s. This is about 30 m/s slower than the zonal winds measured at the time of the Voyager 2 flyby. Tracking its motion from July to November 2015 suggests a longitudinal oscillation of 16° in amplitude with a 90-day period, typical of dark spots on Neptune and similar to the Great Red Spot oscillation in Jupiter. The limited time covered by high-resolution observations only covers one full oscillation and other interpretations of the changing motions could be possible. HST images in September 2015 show the presence of a dark spot at short wavelengths located in the southern flank (planetographic latitude −47.0°) of the bright compact cloud observed throughout 2015. The drift rate of the bright cloud and dark spot translates to a zonal speed of −87.0 ± 2.0 m/s, which matches the Voyager 2 zonal speeds at the latitude of the dark spot. Identification of a few other features in 2015 enabled the extraction of some limited wind information over this period. This work demonstrates the need of frequently monitoring Neptune to understand its atmospheric dynamics and shows excellent opportunities for professional and amateur collaborations.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94919, title ="Io’s Loki Patera: Modeling of three brightening events in 2013–2016", author = "de Kleer, Katherine and de Pater, Imke", journal = "Icarus", volume = "289", pages = "181-198", month = "June", year = "2017", doi = "10.1016/j.icarus.2017.01.038", issn = "0019-1035", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190424-103200188", note = "© 2017 Elsevier. \n\nReceived 1 October 2016, Revised 7 January 2017, Accepted 26 January 2017, Available online 20 February 2017. \n\nThe authors would like to thank A.G. Davies and J. Rathbun for valuable insight at many stages of this work. This research was partially supported by the National Science Foundation grant AST-1313485 to UC Berkeley and by the National Science Foundation Graduate Research Fellowship to K. de Kleer under Grant DGE-1106400. This work made use of the JPL Solar System Dynamics high-precision ephemerides through the HORIZONS system. Results are based in part on data obtained with the W.M. Keck Observatory, which is operated by the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. Results are based in part on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), and Ministério da Ciência, Tecnologia e Inovação (Brazil). The authors extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. Without their generous hospitality, none of the observations presented would have been possible.", revision_no = "9", abstract = "Loki Patera is one of the most dramatically time-variable volcanic features on Io, exhibiting episodic brightening events every 1–3 years that may produce over 15% of Io’s global heat flow. We observed three such brightening events with adaptive optics imaging at the Keck and Gemini N telescopes over the course of 70 nights of observation in 2013–2016. The high cadence and multi-wavelength nature of the observations provides constraints on models for activity at Loki Patera. The Matson et al. (2006) model for Loki Patera as an overturning basaltic magma sea is adapted to fit the observations of all three events. In particular, we adjust the details of the overturn progression, and modify the lava thermal properties to include dependencies on temperature and porosity, to improve the fit to the data. The preferred models find overturn front propagation velocities of 1.2–1.7 km/day, corresponding to resurfacing rates of 1500–2200 m^2/s. The time intervals of 440–540 days between successive events are roughly consistent with the 540-day period calculated by Rathbun et al. (2002) for events prior to 2001. The best coverage was obtained for the 2016 brightening; model fits to this event require a lava bulk thermal conductivity of 0.55–0.75 W/m/K, with the best fit obtained for a value of ∼0.7 W/m/K and an average porosity that decreases during cooling. For all three events, the overturn front appears to propagate around the patera in the clockwise direction, opposite to what has been inferred for past brightening events. There is evidence that the overturn may be more complex than a single propagating wave, perhaps involving multiple simultaneous resurfacing waves as well as portions of the patera that are active even after the nominal bright phase has ended. The measured intensities are anomalously low when Loki Patera is viewed at high emission angles, suggestive of topographic shadowing due to a raised area or the edge of the depression in which the magma sea resides.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/78330, title ="Two Small Transiting Planets and a Possible Third Body Orbiting HD 106315", author = "Crossfield, Ian J. M. and Ciardi, David R.", journal = "Astronomical Journal", volume = "153", number = "6", pages = "Art. No. 255", month = "June", year = "2017", doi = "10.3847/1538-3881/aa6e01", issn = "1538-3881", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170619-123025887", note = "© 2017 The American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. \n\nReceived 2017 January 13; revised 2017 February 13; accepted 2017 February 15; published 2017 May 19. \n\nThis work made use of the SIMBAD database (operated at CDS, Strasbourg, France) and NASA's Astrophysics Data System Bibliographic Services. This research has made use of the NASA Exoplanet Archive and the Infrared Science Archive, which are operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration. Portions of this work were performed at the California Institute of Technology under contract with the National Aeronautics and Space Administration. Some of the data presented herein were obtained at the WM Keck Observatory (which is operated as a scientific partnership among Caltech, UC, and NASA). The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. I.J.M.C. was supported for this work under contract with the Jet Propulsion Laboratory (JPL) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. A.W.H. acknowledges support for this K2 work from a NASA Astrophysics Data Analysis Program grant, support from the K2 Guest Observer Program, and a NASA Key Strategic Mission Support Project. L.M.W. acknowledges support from the Trottier family. \n\nFacility: Kepler, Keck-II (NIRC2), Keck-II (HIRES). \n\nNote added in review:\nWhile preparing this paper, we became aware of another paper describing the identification of HD 106315 as a planet-hosing system (Rodriguez et al. 2017). We are pleased that both groups report consistent results despite the fact that no detailed information was shared prior to submission of the two papers.", revision_no = "18", abstract = "The masses, atmospheric makeups, spin–orbit alignments, and system architectures of extrasolar planets can be best studied when the planets orbit bright stars. We report the discovery of three bodies orbiting HD 106315, a bright (V = 8.97 mag) F5 dwarf targeted by our K2 survey for transiting exoplanets. Two small transiting planets are found to have radii 2.23^(+0.30)_(-0.25)R⊕ and 3.95^(+0.42)_(-0.39)R⊕ and orbital periods 9.55 days and 21.06 days, respectively. A radial velocity (RV) trend of 0.3 ± 0.1 m s^(−1) day^(−1) indicates the likely presence of a third body orbiting HD 106315 with period ≳160 days and mass ≳45 M⊕. Transits of this object would have depths ≳0.1% and are definitively ruled out. Although the star has v sin i = 13.2 km s^(−1), it exhibits a short-timescale RV variability of just 6.4 m s^(−1). Thus, it is a good target for RV measurements of the mass and density of the inner two planets and the outer object's orbit and mass. Furthermore, the combination of RV noise and moderate v sin i makes HD 106315 a valuable laboratory for studying the spin–orbit alignment of small planets through the Rossiter–McLaughlin effect. Space-based atmospheric characterization of the two transiting planets via transit and eclipse spectroscopy should also be feasible. This discovery demonstrates again the power of K2 to find compelling exoplanets worthy of future study.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94936, title ="Multi-phase volcanic resurfacing at Loki Patera on Io", author = "de Kleer, K. and Skrutskie, M.", journal = "Nature", volume = "545", number = "7653", pages = "199-202", month = "May", year = "2017", doi = "10.1038/nature22339", issn = "0028-0836", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190424-141802511", note = "© 2017 Nature Publishing Group. \n\nReceived 31 October 2016. Accepted 29 March 2017. Published 10 May 2017. \n\nThe Large Binocular Telescope (LBT) is an international collaboration among institutions in the United States, Italy and Germany. The LBT Corporation partners are: the University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University; and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota and University of Virginia. The LBT Interferometer is funded by NASA as part of its Exoplanet Exploration program. The LMIRcam instrument is funded by the US NSF through grant NSF AST-0705296. A.G.D., K.d.K. and I.d.P. are partially supported by the NSF grant AST-1313485 to UC Berkeley and by the NSF Graduate Research Fellowship to K.d.K. under grant DGE-1106400. A.G.D. thanks the NASA Outer Planets Research Program for support under grant OPR NNN13D466T. \n\nAuthor Contributions: A.C., A.S., D.D., J.L., M.S., P.H., C.V. and C.E.W. developed and operated the instrumentation used to obtain these observations. A.C., A.S., A.V., D.D., E.S., K.d.K., P.H. and V.B. took the data. A.R., J.L. and M.S. performed the data reduction and calibration. K.d.K. and M.S. analysed the data. A.G.D., I.d.P., J.L., K.d.K. and M.S. wrote the main text and the Methods section. \n\nCode availability: We have opted not to make the code available because the technique described is non-standard and custom routines were developed for the analysis. \n\nData availability: The datasets generated and analysed during this study are available from the corresponding author upon reasonable request. \n\nThe authors declare no competing financial interests.", revision_no = "12", abstract = "The Jovian moon Io hosts the most powerful persistently active volcano in the Solar System, Loki Patera. The interior of this volcanic, caldera-like feature is composed of a warm, dark floor covering 21,500 square kilometres surrounding a much cooler central ‘island’. The temperature gradient seen across areas of the patera indicates a systematic resurfacing process, which has been seen to occur typically every one to three years since the 1980s. Analysis of past data has indicated that the resurfacing progressed around the patera in an anti-clockwise direction at a rate of one to two kilometres per day, and that it is caused either by episodic eruptions that emplace voluminous lava flows or by a cyclically overturning lava lake contained within the patera. However, spacecraft and telescope observations have been unable to map the emission from the entire patera floor at sufficient spatial resolution to establish the physical processes at play. Here we report temperature and lava cooling age maps of the entire patera floor at a spatial sampling of about two kilometres, derived from ground-based interferometric imaging of thermal emission from Loki Patera obtained on 8 March 2015 UT as the limb of Europa occulted Io. Our results indicate that Loki Patera is resurfaced by a multi-phase process in which two waves propagate and converge around the central island. The different velocities and start times of the waves indicate a non-uniformity in the lava gas content and/or crust bulk density across the patera.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94929, title ="Radar observations and shape model of asteroid 16 Psyche", author = "Shepard, Michael K. and Richardson, James", journal = "Icarus", volume = "281", pages = "388-403", month = "January", year = "2017", doi = "10.1016/j.icarus.2016.08.011", issn = "0019-1035", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190424-103201183", note = "© 2016 Elsevier. \n\nAvailable online 12 August 2016. \n\nThe Arecibo Observatory is operated by SRI International under a cooperative agreement with the National Science Foundation (AST-1100968), and in alliance with Ana G. Méndez-Universidad Metropolitana, and the Universities Space Research Association. The Arecibo Planetary Radar Program is supported by the National Aeronautics and Space Administration under Grant No. NNX12AF24G issued through the Near Earth Object Observations program. We thank the Arecibo operators and staff for their help in observing. Some of this work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This material is based in part upon work supported by the National Aeronautics and Space Administration (NASA) under the Science Mission Directorate Research and Analysis Programs. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This paper also includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. Funding for PDS observations, analysis, and publication was provided by NASA grant NNX13AP56G. Work on the asteroid lightcurve database (LCDB) was also funded in part by National Science Foundation grant AST-1507535.", revision_no = "15", abstract = "Using the S-band radar at Arecibo Observatory, we observed 16 Psyche, the largest M-class asteroid in the main belt. We obtained 18 radar imaging and 6 continuous wave runs in November and December 2015, and combined these with 16 continuous wave runs from 2005 and 6 recent adaptive-optics (AO) images (Drummond et al., 2016) to generate a three-dimensional shape model of Psyche. Our model is consistent with a previously published AO image (Hanus et al., 2013) and three multi-chord occultations. Our shape model has dimensions 279\u2009×\u2009232\u2009×\u2009189 km (±\u200910%), D_(eff) =\u2009226\u2009±\u200923 km, and is 6% larger than, but within the uncertainties of, the most recently published size and shape model generated from the inversion of lightcurves (Hanus et al., 2013). Psyche is roughly ellipsoidal but displays a mass-deficit over a region spanning 90° of longitude. There is also evidence for two ∼50–70 km wide depressions near its south pole. Our size and published masses lead to an overall bulk density estimate of 4500\u2009±\u20091400 kgm^(−3). Psyche's mean radar albedo of 0.37\u2009±\u20090.09 is consistent with a near-surface regolith composed largely of iron-nickel and ∼40% porosity. Its radar reflectivity varies by a factor of 1.6 as the asteroid rotates, suggesting global variations in metal abundance or bulk density in the near surface. The variations in radar albedo appear to correlate with large and small-scale shape features. Our size and Psyche's published absolute magnitude lead to an optical albedo of pv =\u20090.15\u2009±\u20090.03, and there is evidence for albedo variegations that correlate with shape features.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94920, title ="Spatial distribution of Io’s volcanic activity from near-IR adaptive optics observations on 100 nights in 2013–2015", author = "de Kleer, Katherine and de Pater, Imke", journal = "Icarus", volume = "280", pages = "405-414", month = "December", year = "2016", doi = "10.1016/j.icarus.2016.06.018", issn = "0019-1035", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190424-103200280", note = "© 2016 Elsevier. \n\nReceived 18 January 2016, Revised 8 June 2016, Accepted 18 June 2016, Available online 25 June 2016. \n\nThe authors would like to thank A. Davies for valuable insight at many stages of this work; A. Davies and an anonymous reviewer for careful reading and thoughtful comments; and J. Rathbun for interesting and helpful discussion throughout. In addition, the authors are grateful to A. Stephens and T. Geballe for supporting the Gemini N observing program, and to the Gemini N observers for collecting the data. This research was partially supported by the National Science Foundation Grant AST-1313485 to UC Berkeley and by the National Science Foundation Graduate Research Fellowship to K. de Kleer under Grant DGE-1106400. This work made use of the JPL Solar System Dynamics high-precision ephemerides through the HORIZONS system. Data were obtained with the W.M. Keck Observatory, which is operated by the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. Without their generous hospitality, none of the observations presented would have been possible.", revision_no = "11", abstract = "The extreme and time-variable volcanic activity on Jupiter’s moon Io is the result of periodic tidal forcing. The spatial distribution of Io’s surface heat flux provides an important constraint on models for tidal heat dissipation, yielding information on interior properties and on the depth at which the tidal heat is primarily dissipated. We analyze the spatial distribution of 48 hot spots based on more than 400 total hot spot detections in adaptive optics images taken on 100 nights in 2013–2015 (data presented in de Kleer and de Pater [2016] Time variability of Io’s volcanic activity from near-IR adaptive optics 13 observations on 100 nights in 2013–2015). We present full surface maps of Io at multiple near-infrared wavelengths for three epochs during this time period, and show that the longitudinal distribution of hot spots has not changed significantly since the Galileo mission. \n\nWe find that hot spots that are persistently active at moderate intensities tend to occur at different latitudes/longitudes than those that exhibit sudden brightening events characterized by high peak intensities and subsequent decay phases. While persistent hot spots are located primarily between ± 30°N, hot spots exhibiting bright eruption events occur primarily between 40° and 65° in both the northern and southern hemispheres. In addition, while persistent hot spots occur preferentially on the leading hemisphere, all bright eruptions were detected on the trailing hemisphere, despite the comparable longitudinal coverage of our observations to both hemispheres. A subset of the bright hot spots which are not intense enough to qualify as outburst eruptions resemble outbursts in terms of temporal evolution and spatial distribution, and may be outbursts whose peak emission went unobserved, or else scaled-down versions of the same phenomenon. A statistical analysis finds that large eruptions are more spatially clustered and occur at higher latitudes than 95% of simulated datasets that assume that eruptions occur at random and independent locations. \n\nThe preferential occurrence of bright, violent eruptions at higher latitudes supports the idea that a deeper magma source supplies these events, as has been previously hypothesized. The monotonic eastward progression of bright eruptions at southern latitudes from 300° to 200°W also suggests a possible eruption triggering mechanism operating across distances of ∼500 km. A comparison to tidal heating models finds a good correspondence between recent models incorporating a partially-fluid interior (Tyler et al. [2015] Astrophys. J., 218–222). and hot spots in the leading hemisphere as well as persistent hot spots. However, hot spots on the trailing hemisphere and bright eruptions do not match these models well, corresponding better to standard deep-mantle heating models (Segatz et al. [1988] Icarus, 75, 187–206) although this match is still imperfect.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94921, title ="Time variability of Io's volcanic activity from near-IR adaptive optics observations on 100 nights in 2013–2015", author = "de Kleer, Katherine and de Pater, Imke", journal = "Icarus", volume = "280", pages = "378-404", month = "December", year = "2016", doi = "10.1016/j.icarus.2016.06.019", issn = "0019-1035", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190424-103200367", note = "© 2016 Elsevier. \n\nReceived 18 January 2016, Revised 8 June 2016, Accepted 18 June 2016, Available online 25 June 2016. \n\nThe authors would like to thank A. Davies for valuable insight at many stages of this work; A. Davies and an anonymous reviewer for careful reading and thoughtful comments; and J. Rathbun for interesting and helpful discussion throughout. In addition, the authors are grateful to A. Stephens and T. Geballe for supporting the Gemini N observing program, and to the Gemini N observers for collecting the data. This research was partially supported by the National Science Foundation grant AST-1313485 to UC Berkeley and by the National Science Foundation Graduate Research Fellowship to K. de Kleer under Grant DGE-1106400. This work made use of the JPL Solar System Dynamics high-precision ephemerides through the HORIZONS system. Data were obtained with the W.M. Keck Observatory, which is operated by the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. Without their generous hospitality, none of the observations presented would have been possible.", revision_no = "10", abstract = "Jupiter’s moon Io is a dynamic target, exhibiting extreme and time-variable volcanic activity powered by tidal forcing from Jupiter. We have conducted a campaign of high-cadence observations of Io with the goal of characterizing its volcanic activity. Between Aug 2013 and the end of 2015, we imaged Io on 100 nights in the near-infrared with adaptive optics on the Keck and Gemini N telescopes, which resolve emission from individual volcanic hot spots. During our program, we made over 400 detections of 48 distinct hot spots, some of which were detected 30+ times. We use these observations to derive a timeline of global volcanic activity on Io, which exhibits wide variability from month to month. The timelines of thermal activity at individual volcanic centers have geophysical implications, and will permit future characterization by others. We evaluate hot spot detection limits and give a simple parameterization of the minimum detectable intensity as a function of emission angle, which can be applied to other analyses. \n\nWe detected three outburst eruptions in August 2013, but no other outburst-scale events were observed in the subsequent ∼90 observations. Either the cluster of events in August 2013 was a rare occurrence, or there is a mechanism causing large events to occur closely-spaced in time. We also detected large eruptions (though not of outburst scale) within days of one another at Kurdalagon Patera and Sethlaus/Gabija Paterae in 2015. As was also seen in the Galileo dataset, the hot spots we detected can be separated into two categories based on their thermal emission: those that are persistently active for 1 year or more at moderate intensity, and those that are only briefly active, are time-variable, and often reach large intensities. A small number of hot spots in the latter category appear and subside in a matter of days, reaching particularly high intensities; although these are not bright enough to qualify as outbursts, their thermal signatures follow the same pattern, suggesting that a similar mechanism may be responsible for these events though at a smaller scale. \n\nTwo eruptions seen at Kurdalagon Patera in January and April 2015 occurred simultaneously with a brightening of the neutral cloud and plasma torus which are sourced from Io’s atmosphere. A plume at Kurdalagon Patera, such as was seen by New Horizons in 2007, could have been responsible for the influx of material that caused these brightenings.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/96299, title ="Retrieving Neptune’s aerosol properties from Keck OSIRIS observations. I. Dark regions", author = "Luszcz-Cook, S. H. and de Kleer, K.", journal = "Icarus", volume = "276", pages = "52-87", month = "September", year = "2016", doi = "10.1016/j.icarus.2016.04.032", issn = "0019-1035", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190611-140325631", note = "© 2016 Elsevier Inc. \n\nReceived 17 November 2015, Revised 2 April 2016, Accepted 19 April 2016, Available online 29 April 2016. \n\nThe data presented were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to conduct observations from this mountain. This work was supported by NSF Grant AST-0908575 to UC Berkeley; SHLC was also supported by NASA Headquarters under the NASA Earth and Space Science Fellowship program - Grant NNX10AT17H; and a Kalbfleisch Postdoctoral Fellowship at the American Museum of Natural History. SHLC would like to thank A. Veicht and D. Zurek for computing assistance and support. The authors would like to thank L. Fletcher for providing his temperature profiles, and two anonymous reviewers for their insightful and valuable comments, which improved this paper.", revision_no = "13", abstract = "We present and analyze three-dimensional data cubes of Neptune from the OSIRIS integral-field spectrograph on the 10-m W.M. Keck II telescope, from 26 July 2009. These data have a spatial resolution of 0.035/pixel and spectral resolution of R ∼3800 in the H (1.47–1.80 µm) and K (1.97–2.38 µm) broad bands. We focus our analysis on regions of Neptune’s atmosphere that are near-infrared dark – that is, free of discrete bright cloud features. We use a forward model coupled to a Markov chain Monte Carlo algorithm to retrieve properties of Neptune’s aerosol structure and methane profile above ∼4 bar in these near-infrared dark regions.\nWe construct a set of high signal-to-noise spectra spanning a range of viewing geometries to constrain the vertical structure of Neptune’s aerosols in a cloud-free latitude band from 2–12°N. We find that Neptune’s cloud opacity at these wavelengths is dominated by a compact, optically thick cloud layer with a base near 3 bar. Using the pyDISORT algorithm for the radiative transfer and assuming a Henyey-Greenstein phase function, we observe this cloud to be composed of low albedo (single scattering albedo =0.45_(−0.01)^(+0.01)), forward scattering (asymmetry parameter g=0.50_(−0.02)^(+0.02)) particles, with an assumed characteristic size of ∼1µm. Above this cloud, we require an aerosol layer of smaller (∼0.1µm) particles forming a vertically extended haze, which reaches from the upper troposphere (0.59_(−0.03)^(+0.04) bar) into the stratosphere. The particles in this haze are brighter (single scattering albedo =0.91_(−0.05)^(+0.06)) and more isotropically scattering (asymmetry parameter g=0.24_(−0.03)^(+0.02)) than those in the deep cloud. When we extend our analysis to 18 cloud-free locations from 20°N to 87°S, we observe that the optical depth in aerosols above 0.5 bar decreases by a factor of 2–3 or more at mid- and high-southern latitudes relative to low latitudes.\nWe also consider Neptune’s methane (CH_4) profile, and find that our retrievalsindicate a strong preference for a low methane relative humidity at pressures where methane is expected to condense. When we include in our fits a parameter for methane depletion below the CH_4 condensation pressure, our preferred solution at most locations is for a methane relative humidity below 10% near the tropopause in addition to methane depletion down to 2.0–2.5 bar. We tentatively identify a trend of lower CH_4 columns above 2.5 bar at mid- and high-southern latitudes over low latitudes, qualitatively consistent with what is found by Karkoschka and Tomasko (2011), and similar to, but weaker than, the trend observed for Uranus.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94928, title ="Io: Eruptions at Pillan, and the time evolution of Pele and Pillan from 1996 to 2015", author = "de Pater, Imke and Laver, Conor", journal = "Icarus", volume = "264", pages = "198-212", month = "January", year = "2016", doi = "10.1016/j.icarus.2015.09.006", issn = "0019-1035", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190424-103201071", note = "© 2015 Elsevier. \n\nReceived 28 April 2015, Revised 1 September 2015, Accepted 3 September 2015, Available online 25 September 2015. \n\nWe are grateful to Alfred McEwen for his review and suggestions for improving this paper. Most of the data presented in this paper were obtained at the W.M. Keck Observatory. We thank Keith Matthews for donating us the first half of the 14 August 2007 night, before our prime target (Uranus) was visible. Two of the data sets presented here (3 April 2007 and 28 June 2010) were retrieved from the publicly available Keck Archive (PI: F. Marchis). The Keck Telescopes are operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. \n\nSeveral data sets were obtained at the Gemini North Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência, Tecnologia e Inovação (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina). Three datasets (2015 mutual occultation events) were obtained with the Infrared Telescope Facility (IRTF), which is operated by the University of Hawaii under contract NNH14CK55B with the National Aeronautics and Space Administration. \n\nOur research was partially supported by the National Science Foundation, NSF Grant AST-1313485 to UC Berkeley. Katherine de Kleer is supported by the National Science Foundation Graduate Research Fellowship under Grant DGE-1106400. Ashley Davies thanks the NASA Outer Planets Research and Planetary Geology and Geophysics Program for support under grants NMO710830 and NMO710931. The authors recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations of Ionian volcanoes from this Hawaiian volcano.", revision_no = "14", abstract = "Observations obtained with the near-infrared camera NIRC2, coupled to the adaptive optics system on the 10-m W.M. Keck II telescope on Mauna Kea, Hawaii, on 14 August 2007 revealed an active and highly-energetic eruption at Pillan at 245.2 ± 0.7°W and 8.5 ± 0.5°S. A one-temperature blackbody fit to the data revealed a (blackbody) temperature of 840 ± 40 K over an area of 17 km^2, with a total power output of ∼500 GW. Using Davies’ (Davies, A.G. [1996]. Icarus 124(1), 45–61) Io Flow Model, we find that the oldest lava present is less than 1-2 h old, having cooled down from the eruption temperature of >1400 K to ∼710 K; this young hot lava suggests that an episode of lava fountaining was underway. In addition to an examination of this eruption, we present data of the Pele and Pillan volcanoes obtained with the same instrument and telescope from 2002 through 2015. These data reveal another eruption at Pillan on UT 28 June 2010. Model fits to this eruption yield a blackbody temperature of 600–700 K over an area of ∼60 km^2, radiating over 600 GW. On UT 18 February 2015 an energetic eruption was captured by the InfraRed Telescope Facility (IRTF) via mutual event occultations. The eruption took place at 242.7 ± 1°W and 12.4 ± 1°S, i.e., in the eastern part of Pillan Patera. Subsequent observations showed a gradual decrease in the intensity of the eruption. Images obtained with the Keck telescope on 31 March and 5 May 2015 revealed that the locations of the eruption had shifted by 120–160 km to the NW. \n\nIn contrast to the episodicity of Pillan, Pele has been persistent, observed in every appropriate 4.7 μm observation. Pele was remarkably consistent in its thermal emission from the Galileo era through February 2002, when a blackbody temperature of 940 ± 40 K and an area of 6.5 km^2 was measured. Since that time, however, the radiant flux from what is likely a apparently large, overturning lava lake has gradually subsided over the next decade by a factor of ∼4, while the location of the thermal source was moving back and forth between areas roughly ∼100 km to the W of the 2002 location and an area roughly ∼100 km to the SE of the 2002 location.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94925, title ="Clouds and aerosols on Uranus: Radiative transfer modeling of spatially-resolved near-infrared Keck spectra", author = "de Kleer, Katherine and Luszcz-Cook, Statia", journal = "Icarus", volume = "256", pages = "120-137", month = "August", year = "2015", doi = "10.1016/j.icarus.2015.04.021", issn = "0019-1035", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190424-103200744", note = "© 2015 Elsevier. \n\nReceived 1 December 2014, Revised 3 April 2015, Accepted 13 April 2015, Available online 20 April 2015. \n\nThe authors would like to thank L. Sromovsky for helpful discussion and suggestions at various stages of this work. The near-infrared data were obtained with the W.M. Keck Observatory, which is operated by the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. Without their generous hospitality, none of the observations presented would have been possible. This research was supported in part by NASA’s Planetary Astronomy Program under Grant NNX07AK70G to the University of California, Berkeley. K. de Kleer is additionally supported by the National Science Foundation Graduate Research Fellowship under Grant DGE-1106400. S. Luszcz-Cook is supported by the Kalbfleisch Postodoctoral Fellowship at the American Museum of Natural History. This research has also made use of the SIMBAD database, operated at CDS, Strasbourg, France.", revision_no = "9", abstract = "We observed Uranus in the near-infrared H and K′ bands (1.47–2.38 m) in 2010 and 2011 with the OSIRIS imaging spectrograph on the Keck II telescope with adaptive optics. In 2010, three years past the equinox, we had a good view of the north polar region while still having access to southern latitudes down to 70°S. In 2011 our observations focused on a moderately bright discrete cloud feature in the middle of the bright circumpolar band at 45°N. \n\nThe spatial and spectral resolution of our data allow us to retrieve atmospheric parameters between ∼65°S and 75°N via radiative transfer modeling. We test vertical aerosol profiles with combinations of diffuse and compact scattering layers, and find that we can reproduce our equatorial data for a range of cases, provided the deepest detectable aerosol layer is compact and located between 2 and 3 bars, with the higher cloud altitudes corresponding to models with higher methane deep volume mixing ratios. Using a parameterized atmosphere with a diffuse upper haze and a moderately compact lower cloud, we find that both the haze and the cloud reach their maximal optical depth just north of the equator and thin toward the poles. When we fix the abundance of methane with latitude, we find that the bottom cloud shifts to shallower depths at higher latitudes in both hemispheres; for a methane profile with a deep volume mixing ratio of 2.22%, the cloud rises from the 3-bar level equatorward of ±20° to above 2 bars by ±60°. However, when we allow the tropospheric methane abundance to vary according to a parameterized vertical profile, we find that the lower cloud depth is stable in latitude while the methane becomes increasingly depleted toward both poles. In both cases, we find denser aerosol layers and higher methane abundances in the northern hemisphere than the southern, consistent with a seasonal post-equinox trend. In particular, the bright band near 45°N is relatively undepleted in methane, and represents a local peak in the opacity and altitude of the lower cloud. The cloud feature we detected in 2011 falls in the middle of this band. This feature extends from a depth of ∼1.3 bars up to the 0.5-bar level. Both CH4 and H2S are expected to condense below this level; if the cloud has formed as the result of a convective upwelling event, these are the most likely condensation species.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/58003, title ="A Nearby M Star with Three Transiting Super-Earths Discovered by K2", author = "Crossfield, Ian J. M. and Howard, Andrew W.", journal = "Astrophysical Journal", volume = "804", number = "1", pages = "Art. No. 10", month = "May", year = "2015", doi = "10.1088/0004-637X/804/1/10", issn = "0004-637X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150604-125434670", note = "© 2015 The American Astronomical Society. \n\nReceived 2015 January 15; Accepted 2015 February 16; Published 2015 April 23. \n\nWe thank Geoff Marcy, Evan Sinukoff, and Charles Beichman for helpful conversations; Vishnu Reddy for swapping SpeX time; and Steve Bryson and our referee Don Pollacco for useful comments that improved the quality of this manuscript. A. W.H. acknowledges NASA grant No. NNX12AJ23G, and S.L. acknowledges NSF grant No. AST 09-08419. This work made use of the SIMBAD database (operated at CDS, Strasbourg, France); NASA’s Astrophysics Data System Bibliographic Services; the Authorea collaborative writing website; the NASA Exoplanet Archive; and Infrared Science Archive, and data products from the Two Micron All Sky Survey (2MASS), the APASS database, the SDSS-III project, the Digitized Sky Survey, and the Wide-Field Infrared Survey Explorer. Portions of this work were performed at the California Institute of Technology under contract with the National Aeronautics and Space Administration. Some of the data presented herein were obtained at the W. M. Keck Observatory (which is operated as a scientific partnership among Caltech, UC, and NASA) and at the Infrared Telescope Facility (IRTF, operated by UH under NASA contract NNH14CK55B). The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. \n\nFacilities: APF (Levy), IRTF (SPEX), Keck: II (NIRC2), Kepler, NTT (EFOSC2)", revision_no = "24", abstract = "Small, cool planets represent the typical end-products of planetary formation. Studying the architectures of these systems, measuring planet masses and radii, and observing these planets' atmospheres during transit directly informs theories of planet assembly, migration, and evolution. Here we report the discovery of three small planets orbiting a bright (K_s = 8.6 mag) M0 dwarf using data collected as part of K2, the new ecliptic survey using the re-purposed Kepler spacecraft. Stellar spectroscopy and K2 photometry indicate that the system hosts three transiting planets with radii 1.5–2.1 R_⊕, straddling the transition region between rocky and increasingly volatile-dominated compositions. With orbital periods of 10–45 days the planets receive just 1.5–10× the flux incident on Earth, making these some of the coolest small planets known orbiting a nearby star; planet d is located near the inner edge of the system's habitable zone. The bright, low-mass star makes this system an excellent laboratory to determine the planets' masses via Doppler spectroscopy and to constrain their atmospheric compositions via transit spectroscopy. This discovery demonstrates the ability of K2 and future space-based transit searches to find many fascinating objects of interest.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94934, title ="Spatially Resolved M-band Emission from Io's Loki Patera–Fizeau Imaging at the 22.8 m LBT", author = "Conrad, Albert and de Kleer, Katherine", journal = "Astronomical Journal", volume = "149", number = "5", pages = "Art. No. 175", month = "May", year = "2015", doi = "10.1088/0004-6256/149/5/175", issn = "1538-3881", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190424-141802194", note = "© 2015. The American Astronomical Society. \n\nReceived 2014 December 8; accepted 2015 March 17; published 2015 April 30. \n\nThe research was partially supported by the National Science Foundation, NSF Grant AST-1313485 to UC Berkeley, and by the National Science Foundation Graduate Research Fellowship under Grant DGE-1106400. Development of LMIRCam was supported by NSF grant AST-0705296. \n\n1. The LBTI is funded by the National Aeronautics and Space Administration as part of its Exoplanet Exploration program. \n\n2. The LBT is an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy, LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University; and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota, and University of Virginia.", revision_no = "10", abstract = "The Large Binocular Telescope Interferometer mid-infrared camera, LMIRcam, imaged Io on the night of 2013 December 24 UT and detected strong M-band (4.8 μm) thermal emission arising from Loki Patera. The 22.8 m baseline of the Large Binocular Telescope provides an angular resolution of ~32 mas (~100 km at Io) resolving the Loki Patera emission into two distinct maxima originating from different regions within Loki's horseshoe lava lake. This observation is consistent with the presence of a high-temperature source observed in previous studies combined with an independent peak arising from cooling crust from recent resurfacing. The deconvolved images also reveal 15 other emission sites on the visible hemisphere of Io including two previously unidentified hot spots.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94926, title ="Near-infrared monitoring of Io and detection of a violent outburst on 29 August 2013", author = "de Kleer, Katherine and de Pater, Imke", journal = "Icarus", volume = "242", pages = "352-364", month = "November", year = "2014", doi = "10.1016/j.icarus.2014.06.006", issn = "0019-1035", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190424-103200843", note = "© 2014 Elsevier. \n\nReceived 27 February 2014, Revised 1 June 2014, Accepted 5 June 2014, Available online 24 June 2014. \n\nThe data presented in this paper were obtained at the Gemini N Telescope and as a Visiting Astronomer at NASA’s Infrared Telescope Facility, under programs GN-2013B-DD-3 and 2013B-030 respectively. We thank the Gemini Director, Markus Kissler-Patig, and the Deputy Director and Head of Science, Nancy Levenson, for providing us with DD time to observe Io during about a dozen nights following the initial detection of the eruption. We thank the IRTF Director, Alan Tokunaga, for providing us with DD time to simultaneously observe Io on four of these nights. Gemini Observatory is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência, Tecnologia e Inovação (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina). The Infrared Telescope Facility is operated by the University of Hawaii under Cooperative Agreement No. NNX-08AE38A with the National Aeronautics and Space Administration, Science Mission Directorate, Planetary Astronomy Program. Our research was partially supported by the National Science Foundation, NSF Grant AST-1313485 to UC Berkeley, and by the National Science Foundation Graduate Research Fellowship under Grant DGE-1106400. Ashley Davies thanks the NASA Outer Planets Research and Planetary Geology and Geophysics Programs for support. The authors recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations of Ionian volcanoes from this Hawaiian volcano.", revision_no = "9", abstract = "We present initial data from our campaign to monitor Io in the near-infrared, beginning in August 2013, using 3.8-μm adaptive optics imaging at Gemini N and 2–5 μm disk-integrated spectroscopy at NASA’s IRTF. Conducted during 2013–2014, these observations are coincident with the ISAS/JAXA EXCEED mission’s continuous monitoring of the Io plasma torus and will enable the speculated effects of volcanic outgassing on the torus to be observed directly, in addition to enabling an assessment of the frequency and properties of large-scale outbursts. On 29 August 2013 we detected a powerful eruption (designated 201308C) on Io at 223.5 ± 2.6°W, 29.1 ± 1.8°N. Emitting between 15 and >25 TW, this event is one of the most powerful eruptions ever seen on Io and falls into the rare “outburst” class. This was the third eruption of this type seen on Io in August 2013, an unprecedented occurrence. Also unprecedented was the charting of the decay in thermal emission over the subsequent days and weeks. Modeling of the outburst spectrum places a lower bound of 1200–1300 K on the eruption temperature, and is suggestive of temperatures 1900 K or higher, typically associated with ultramafic lava composition. The eruption is likely a highly energetic, high-volume lava fountain event.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94924, title ="Near-infrared spectra of the uranian ring system", author = "de Kleer, Katherine and de Pater, Imke", journal = "Icarus", volume = "226", number = "1", pages = "1038-1044", month = "September", year = "2013", doi = "10.1016/j.icarus.2013.07.016", issn = "0019-1035", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190424-103200657", note = "© 2013 Published by Elsevier. \n\nReceived 25 September 2012, Revised 5 July 2013, Accepted 10 July 2013, Available online 22 July 2013. \n\nThe authors thank Dr. Phil Nicholson and Dr. Erich Karkoschka for their careful reviews and valuable input regarding ring particle reflectivities in particular. The near-infrared data were obtained with the W.M. Keck Observatory, which is operated by the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. Without their generous hospitality, none of the observations presented would have been possible. This research has also made use of the SIMBAD database, operated at CDS, Strasbourg, France. This research was supported by NASA’s Planetary Astronomy Program under Grant NNX07AK70G to the University of California, Berkeley.", revision_no = "12", abstract = "We present the first high-resolution near-infrared (1.18–2.38 μm) spectrum of the rings of Uranus, as observed with adaptive optics on the W.M. Keck II telescope in August 2010. We derive ring equivalent widths, as well as ring and particle reflectivities for the ∊ ring and ringlet groups based on H- and K-band data. We find the rings to be gray, indicating that they are dominated by large particles rather than dust, and we find no evidence for water ice. We present a reflectivity spectrum for the ∊ ring alone, which we also find to be consistent with a flat spectrum. We derive H-band ring particle reflectivities of 0.022 ± 0.010, 0.051 ± 0.009 0.042 ± 0.012, and 0.043 ± 0.001 and K-band ring particle reflectivities of 0.016 ± 0.010, 0.034 ± 0.012, 0.047 ± 0.008 and 0.041 ± 0.002 for the 456, αβ, ηγδ, and ∊ ring groups. Previous observations have found ring particle reflectivities in the 0.033–0.044 range (de Pater, I., Gibbard, S., Macintosh, B.A., Roe, H.G. [2002]. Icarus 160, 359–374; Gibbard, S.G., de Pater, I., Hammel, H.B. [2005]. Icarus 174, 253–262), and are generally consistent with our results.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94940, title ="CfA4: Light Curves for 94 Type Ia Supernovae", author = "Hicken, Malcolm and de Kleer, Kathy", journal = "Astrophysical Journal Supplement Series", volume = "200", number = "2", pages = "Art. No. 12", month = "June", year = "2012", doi = "10.1088/0067-0049/200/2/12", issn = "0067-0049", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190424-141803208", note = "© 2012. The American Astronomical Society. \n\nReceived 2012 February 14; accepted 2012 April 5; published 2012 May 17. \n\nWe thank the staff at FLWO for their dedicated work in maintaining the 1.2 m telescope and instruments. We also thank M. Stritzinger, W. Li, and M. Ganeshalingam for help in comparing the CfA4 sample with the CSP2 and LOSS samples. Finally, we appreciate discussions with K. Mandel. This work has been supported, in part, by NSF grants AST0606772 and AST0907903 to Harvard University. \n\nFacility: FLWO:1.2m - Fred Lawrence Whipple Observatory's 1.2 meter Telescope", revision_no = "9", abstract = "We present multi-band optical photometry of 94 spectroscopically confirmed Type Ia supernovae (SNe Ia) in the redshift range 0.0055-0.073, obtained between 2006 and 2011. There are a total of 5522 light-curve points. We show that our natural-system SN photometry has a precision of lesssim 0.03 mag in BVr'i', ≾ 0.06 mag in u', and ≾ 0.07 mag in U for points brighter than 17.5 mag and estimate that it has a systematic uncertainty of 0.014, 0.010, 0.012, 0.014, 0.046, and 0.073 mag in BVr'i'u'U, respectively. Comparisons of our standard-system photometry with published SN Ia light curves and comparison stars reveal mean agreement across samples in the range of ~0.00-0.03 mag. We discuss the recent measurements of our telescope-plus-detector throughput by direct monochromatic illumination by Cramer et al. This technique measures the whole optical path through the telescope, auxiliary optics, filters, and detector under the same conditions used to make SN measurements. Extremely well characterized natural-system passbands (both in wavelength and over time) are crucial for the next generation of SN Ia photometry to reach the 0.01 mag accuracy level. The current sample of low-z SNe Ia is now sufficiently large to remove most of the statistical sampling error from the dark-energy error budget. But pursuing the dark-energy systematic errors by determining highly accurate detector passbands, combining optical and near-infrared (NIR) photometry and spectra, using the nearby sample to illuminate the population properties of SNe Ia, and measuring the local departures from the Hubble flow will benefit from larger, carefully measured nearby samples.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94927, title ="Keck adaptive optics images of Jupiter’s north polar cap and Northern Red Oval", author = "de Pater, Imke and Wong, Michael H.", journal = "Icarus", volume = "213", number = "2", pages = "559-563", month = "June", year = "2011", doi = "10.1016/j.icarus.2011.03.006", issn = "0019-1035", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190424-103200979", note = "© 2011 Elsevier. \n\nReceived 17 December 2010, Revised 28 February 2011, Accepted 4 March 2011, Available online 21 March 2011. \n\nAll data were obtained with the W.M. Keck Observatory, which is operated by the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. We benefitted greatly from the use of JPL’s Horizons system and SETI’s Planetary Rings Node. The authors extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. Without their generous hospitality, none of the observations presented would have been possible.", revision_no = "9", abstract = "We present observations at near-infrared wavelengths (1–5 μm) of Jupiter’s north polar region and Northern Red Oval (NN-LRS-1). The observations were taken with the near-infrared camera NIRC2 coupled to the adaptive optics system on the 10-m W.M. Keck Telescope on UT 21 August 2010. At 5-μm Jupiter’s disk reveals considerable structure, including small bright rings which appear to surround all small vortices. It is striking, though, that no such ring is seen around the Northern Red Oval. In de Pater et al. [2010a. Icarus 210, 742–762], we showed that such rings also exist around all small vortices in Jupiter’s southern hemisphere, and are absent around the Great Red Spot and Red Oval BA. We show here that the vertical structure and extent of the Northern Red Oval is very similar to that of Jupiter’s Red Oval BA. These new observations of the Northern Red Oval, therefore, support the idea of a dichotomy between small and large anticyclones, in which ovals larger than about two Rossby deformation radii do not have 5-μm bright rings. In de Pater et al. [2010a. Icarus 210, 742–762], we explained this difference in terms of the secondary circulations within the vortices. We further compare the brightness distribution of our new 5-μm images with previously published radio observations of Jupiter, highlighting the depletion of NH_3 gas over areas that are bright at 5 μm.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/36197, title ="A Prograde, Low-inclination Orbit for the Very Hot Jupiter WASP-3b", author = "Tripathi, Anjali and Winn, Joshua N.", journal = "Astrophysical Journal", volume = "715", number = "1", pages = "421-428", month = "May", year = "2010", doi = "10.1088/0004-637X/715/1/421", issn = "0004-637X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130107-103218073", note = "© 2010 American Astronomical Society. \n\nReceived 2009 November 20; accepted 2010 April 3; published 2010 April 28. \n\nSome of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. We thank N. Madhusudhan, Michael L. Stevens, and Robert Noyes for helpful discussions. We are grateful to the anonymous referee for helping to clarify the interpretation of the RV spike. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. A.T. and K.dK. thank the MIT UROP Endowment Fund and Office for financial support. J.N.W. is grateful to the NASA Origins program for support through\ngrants NNX09AD36G and NNX09AB33G, and to the MIT Class of 1942 for a Career Development Professorship. J.A.J. is an NSF Astronomy and Astrophysics Postdoctoral Fellow with support from the NSF grant AST-0702821. \n\nFacilities: FLWO:1.2m, UH:2.2m, Keck:I ", revision_no = "21", abstract = "We present new spectroscopic and photometric observations of the transiting exoplanetary system WASP-3. Spectra obtained during two separate transits exhibit the Rossiter-McLaughlin (RM) effect and allow us to estimate the sky-projected angle between the planetary orbital axis and the stellar rotation axis, λ = 3.3^(+2.5)_(–4.4) deg. This alignment between the axes suggests that WASP-3b has a low orbital inclination relative to the equatorial plane of its parent star. During our first night of spectroscopic measurements, we observed an unexpected redshift briefly exceeding the expected sum of the orbital and RM velocities by 140 m s^(–1). This anomaly could represent the occultation of material erupting from the stellar photosphere, although it is more likely to be an artifact caused by moonlight scattered into the spectrograph.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/96298, title ="Leonids 2006 observations of the tail of trails: Where is the comet fluff?", author = "Jenniskens, P. and de Kleer, K.", journal = "Icarus", volume = "196", number = "1", pages = "171-183", month = "July", year = "2008", doi = "10.1016/j.icarus.2008.02.026", issn = "0019-1035", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190611-134954300", note = "© 2008 Elsevier Inc. \n\nReceived 22 October 2007, Revised 4 February 2008, Available online 8 April 2008. \n\nThe 2006 Leonid campaign was made possible by NASA's Planetary Astronomy program. K.d.K. received a NSF grant for the SETI Institute REU program. J.M.T.-R. thanks the MEC for a JdC research grant. J.V. received support from Bill Reach at IPAC. We thank operators at CINES (France) for their assistance in using the super-computer for simulations. We also thank Jun-ichi Watanabe and Margaret Campbell-Brown for careful reviews of this paper.", revision_no = "10", abstract = "In 2006, Earth encountered a trail of dust left by Comet 55P/Tempel-Tuttle two revolutions ago, in A.D. 1932. The resulting Leonid shower outburst was observed by low light level cameras from locations in Spain. The outburst peaked on 2006 Nov. 19d 04h39m ± 3m UT (predicted: 19d 04h50m ± 15m UT), with a FWHM of 43 ± 10 min (predicted: 38 min), at a peak rate of ZHR=80±10/h (predicted: 50–200 per hour). A low level background of older and brighter Filament Leonids (χ∼2.1) was also present, which dominated rates for Leonids brighter than magnitude +4. The 1932-dust outburst was detected among Leonids of +0 magnitude and brighter. These outburst Leonids were much brighter than expected, with a magnitude distribution index χ=2.60±0.15 (predicted: χ=3.47 and up). Trajectories and orbits of 24 meteors were calculated, most of which are part of the Filament component. Those that were identified as 1932-dust grains penetrated just as deep as Leonids in past encounters. We conclude that larger meteoroids than expected were present in the tail of the 1932-dust trail and meteoroids did not end up there because of low density. We also find that the radiant position of meteors in the Filament component scatter in a circle with radius 0.39°, which is wider than in 1998, when the diameter was 0.09°. This supports the hypothesis that the Filament component consists of meteoroids in mean-motion resonances.", }