@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/104356, title ="Constraints on Pluto’s H and CH₄ profiles from New Horizons Alice Lyα observations", author = "Gladstone, G. Randall and Kammer, Joshua A.", journal = "Icarus", volume = "356", pages = "Art. No. 113973", month = "March", year = "2021", doi = "10.1016/j.icarus.2020.113973", issn = "0019-1035", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200713-123919818", note = "© 2020 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license. \n\nReceived 4 April 2020, Revised 25 June 2020, Accepted 5 July 2020, Available online 11 July 2020. \n\nWe thank Tanguy Bertrand and Francois Forget for useful discussions, and the reviewers for useful comments. This work was supported by NASA through contract NASW02008 to SwRI.", revision_no = "14", abstract = "The Alice spectrograph on New Horizons performed several far-ultraviolet (FUV) airglow observations during the July 2015 flyby of Pluto. One of these observations, named PColor2, was a short (226 s) scan across the dayside disk of Pluto from a range of ∼34,000 km, at about 40 minutes prior to closest approach. The brightest observed FUV airglow signal at Pluto is the Lyman alpha (Lyα) emission line of atomic hydrogen, which arises primarily through the resonant scattering of solar Lyα by H atoms in the upper atmosphere, with a brightness of about 30 Rayleighs. Pluto appears dark against the much brighter (∼100 Rayleigh) sky background; this sky background is likewise the result of resonantly scattered solar Lyα, in this case by H atoms in the interplanetary medium (IPM). Here we use an updated photochemical model and a resonance line radiative transfer model to perform detailed simulations of the Lyα emissions observed in the Alice PColor2 scan. The photochemical models show that H and CH₄ abundances in Pluto’s upper atmosphere are a very strong function of the near-surface mixing ratio of CH₄, and could provide a useful way to remotely monitor seasonal climate variations in Pluto’s lower atmosphere. The morphology of the PColor2 Lyα emissions provides constraints on the current abundance profiles of H atoms and CH₄ molecules in Pluto’s atmosphere, and indicate that the globally averaged near-surface mixing ratio of CH₄ is currently close to 0.4%. This new result thus provides independent confirmation of one of the primary results from the solar occultation, also observed with the New Horizons Alice ultraviolet spectrograph.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/104455, title ="Global climate model occultation lightcurves tested by August 2018 ground-based stellar occultation", author = "Chen, Sihe and Young, Eliot F.", journal = "Icarus", volume = "356", pages = "Art. No. 113976", month = "March", year = "2021", doi = "10.1016/j.icarus.2020.113976", issn = "0019-1035", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200720-130843170", note = "© 2020 Elsevier Inc. \n\nReceived 21 December 2019, Revised 29 June 2020, Accepted 9 July 2020, Available online 19 July 2020. \n\nThis work is supported in part by NASA 000329-P2232440 to Caltech, and by NSF 1616115 and NASA SSO 80NSSC19K0824 to SwRI. \n\nThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.", revision_no = "16", abstract = "Pluto's atmospheric profiles (temperature and pressure) have been studied for decades from stellar occultation lightcurves. In this paper, we look at recent Pluto Global Climate Model (GCM) results (3D temperature, pressure, and density fields) from Bertrand et al. (2020) and use the results to generate model observer's plane intensity fields (OPIF) and lightcurves by using a Fourier optics scheme to model light passing through Pluto's atmosphere (Young, 2012). This approach can accommodate arbitrary atmospheric structures and 3D distributions of haze. We compared the GCM model lightcurves with the lightcurves observed during the 15-AUG-2018 Pluto stellar occultation. We find that the climate scenario which best reproduces the observed data includes a N2 ice mid latitude band in the southern hemisphere. We have also studied different haze and P/T ratio profiles: the haze effectively reduces the central flash strength, and a lower P/T ratio both reduces the central flash strength and incurs anomalies in the shoulders of the central flash.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/106894, title ="Even More Rapidly Rotating Pre-main-sequence M Dwarfs with Highly Structured Light Curves: An Initial Survey in the Lower Centaurus-Crux and Upper Centaurus-Lupus Associations", author = "Stauffer, John and Rebull, Luisa M.", journal = "Astronomical Journal", volume = "161", number = "2", pages = "Art. No. 60", month = "February", year = "2021", doi = "10.3847/1538-3881/abc7c6", issn = "1538-3881", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201203-151008360", note = "© 2021 The American Astronomical Society. \n\nReceived 2020 September 15; revised 2020 November 2; accepted 2020 November 3; published 2021 January 11. \n\nSome of the data presented in this paper were obtained from MAST. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contracts. This research has made use of the NASA/IPAC Infrared Science Archive (IRSA), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research has made use of NASA's Astrophysics Data System (ADS) Abstract Service, and of the SIMBAD database, operated at CDS, Strasbourg, France. This research has made use of data products from 2MASS, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, funded by the National Aeronautics and Space Administration and the National Science Foundation. The 2MASS data are served by the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This publication makes use of data products from WISE, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. \n\nFacilities: TESS - , Exoplanet Archive - , IRSA - , 2MASS - , WISE. -", revision_no = "21", abstract = "Using K2, we recently discovered a new type of periodic photometric variability while analyzing the light curves of members of Upper Sco. The 23 exemplars of this new variability type are all mid-M dwarfs, with short rotation periods. Their phased light curves have one or more broad flux dips or multiple arcuate structures which are not explicable by photospheric spots or eclipses by solid bodies. Now, using Transiting Exoplanet Survey Satellite data, we have searched for this type of variability in the other major sections of Sco-Cen, Upper Centaurus-Lupus (UCL), and Lower Centaurus-Crux (LCC). We identify 28 stars with the same light curve morphologies. We find no obvious difference between the Upper Sco and the UCL/LCC representatives of this class in terms of their light curve morphologies, periods, or variability amplitudes. The physical mechanism behind this variability is unknown, but as a possible clue we show that the rapidly rotating mid-M dwarfs in UCL/LCC have slightly different colors from the slowly rotating M dwarfs—they either have a blue excess (hot spots?) or a red excess (warm dust?). One of the newly identified stars (TIC242407571) has a very striking light curve morphology. At about every 0.05 in phase are features that resemble icicles. The icicles arise because there is a second periodic system whose main feature is a broad flux dip. Using a toy model, we show that the observed light curve morphology results only if the ratio of the two periods and the flux-dip width are carefully arranged.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/106978, title ="Inverse tides in pulsating binary stars", author = "Fuller, Jim", journal = "Monthly Notices of the Royal Astronomical Society", volume = "501", number = "1", pages = "483-490", month = "February", year = "2021", doi = "10.1093/mnras/staa3636", issn = "0035-8711", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201209-113410261", note = "© 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. \n\nAccepted 2020 November 12. Received 2020 October 21; in original form 2020 August 24. Published: 21 November 2020. \n\nI thank the anonymous referee for a very careful reading and thoughtful report. I am thankful for support through an Innovator Grant from The Rose Hills Foundation, and the Sloan Foundation through grant FG-2018-10515. \n\nData Availability: Data and source code are available upon request to the authors.", revision_no = "31", abstract = "In close binary stars, the tidal excitation of pulsations typically dissipates energy, causing the system to evolve towards a circular orbit with aligned and synchronized stellar spins. However, for stars with self-excited pulsations, we demonstrate that tidal interaction with unstable pulsation modes can transfer energy in the opposite direction, forcing the spins of the stars away from synchronicity, and potentially pumping the eccentricity and spin–orbit misalignment angle. This ‘inverse’ tidal process only occurs when the tidally forced mode amplitude is comparable to the mode’s saturation amplitude, and it is thus most likely to occur in main-sequence gravity mode pulsators with orbital periods of a few days. We examine the long-term evolution of inverse tidal action, finding the stellar rotation rate can potentially be driven to a very large or very small value, while maintaining a large spin–orbit misalignment angle. Several recent asteroseismic analyses of pulsating stars in close binaries have revealed extremely slow core rotation periods, which we attribute to the action of inverse tides.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/105415, title ="The TESS-Keck Survey. II. An Ultra-short-period Rocky Planet and Its Siblings Transiting the Galactic Thick-disk Star TOI-561", author = "Weiss, Lauren M. and Dai, Fei", journal = "Astronomical Journal", volume = "161", number = "2", pages = "Art. No. 56", month = "February", year = "2021", doi = "10.3847/1538-3881/abd409", issn = "1538-3881", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200916-112902099", note = "© 2021 The American Astronomical Society. \n\nReceived 2020 September 4; revised 2020 December 7; accepted 2020 December 14; published 2021 January 11. \n\nWe thank the time assignment committees of the University of California, the California Institute of Technology, NASA, and the University of Hawaii for supporting the TESS-Keck Survey with observing time at the W. M. Keck Observatory and on the Automated Planet Finder. \n\nWe thank NASA for funding associated with our NASA-Keck Key Strategic Mission Support project. We gratefully acknowledge the efforts and dedication of the Keck Observatory staff for support of HIRES and remote observing. We recognize and acknowledge the cultural role and reverence that the summit of Maunakea has within the indigenous Hawaiian community. We are deeply grateful to have the opportunity to conduct observations from this mountain. \n\nWe thank Ken and Gloria Levy, who supported the construction of the Levy Spectrometer on the Automated Planet Finder. We thank the University of California and Google for supporting Lick Observatory and the UCO staff for their dedicated work scheduling and operating the telescopes of Lick Observatory. This paper is based on data collected by the TESS mission. Funding for the TESS mission is provided by the NASA Explorer Program. We acknowledge the use of public TESS Alert data from pipelines at the TESS Science Office and at the TESS Science Processing Operations Center. We thank David Latham for organizing the TESS community follow-up program, which brought together the widespread authorship and diversity of resources presented in this manuscript. \n\nThe work includes observations obtained at the international Gemini Observatory, a program of NSF's NOIRLab acquired through the Gemini Observatory Archive at NSF's NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf of the Gemini Observatory partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnología e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). Data were collected under program GN-2019A-LP-101. Observations in the paper made use of the High-Resolution Imaging instrument Zorro. Zorro was funded by the NASA Exoplanet Exploration Program and built at the NASA Ames Research Center by Steve B. Howell, Nic Scott, Elliott P. Horch, and Emmett Quigley. Zorro was mounted on the Gemini-South telescope of the international Gemini Observatory. Observations also made use of the NIRI instrument, which is mounted at Gemini-North. The Gemini-North telescope is located within the Maunakea Science Reserve and adjacent to the summit of Maunakea. We are grateful for the privilege of observing the universe from a place that is unique in both its astronomical quality and its cultural significance. \n\nThis work makes use of observations from the LCOGT network. This article is based on observations made with the MuSCAT2 instrument, developed by ABC, at Telescopio Carlos Sánchez operated on the island of Tenerife by the IAC in the Spanish Observatorio del Teide. This work is partly supported by JSPS KAKENHI grant Nos. JP17H04574, JP18H01265, and JP18H05439, and JST PRESTO grant No. JPMJPR1775. This work makes use of data collected under the NGTS project at the ESO La Silla Paranal Observatory. The NGTS facility is operated by the consortium institutes with support from the UK Science and Technology Facilities Council (STFC) projects ST/M001962/1 and ST/S002642/1. \n\nThis work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. J.S.J. acknowledges support by FONDECYT grant 1201371, and partial support from CONICYT project Basal AFB-170002. J.I.V. acknowledges support of CONICYT-PFCHA/Doctorado Nacional-21191829. \n\nThis research has made use of the Exoplanet Follow-up Observing Program (ExoFOP), which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration. Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center for the production of the SPOC data products. \n\nL.M.W. is supported by the Beatrice Watson Parrent Fellowship and NASA ADAP Grant 80NSSC19K0597. D.H. acknowledges support from the Alfred P. Sloan Foundation, the National Aeronautics and Space Administration (80NSSC18K1585, 80NSSC19K0379), and the National Science Foundation (AST-1717000). E.A.P. acknowledges the support of the Alfred P. Sloan Foundation. C.D.D. acknowledges the support of the Hellman Family Faculty Fund, the Alfred P. Sloan Foundation, the David & Lucile Packard Foundation, and the National Aeronautics and Space Administration via the TESS Guest Investigator Program (80NSSC18K1583). I.J.M.C. acknowledges support from the NSF through grant AST-1824644. Z.R.C. acknowledges support from the TESS Guest Investigator Program (80NSSC18K18584). A.C. acknowledges support from the National Science Foundation through the Graduate Research Fellowship Program (DGE 1842402). P.D. acknowledges support from a National Science Foundation Astronomy and Astrophysics Postdoctoral Fellowship under award AST-1903811. A.B. is supported by the NSF Graduate Research Fellowship, grant No. DGE 1745301. R.A.R. is supported by the NSF Graduate Research Fellowship, grant No. DGE 1745301. M.R.K. is supported by the NSF Graduate Research Fellowship, grant No. DGE 1339067. J.N.W. thanks the Heising Simons Foundation for support. \n\nFacilities: TESS - , Keck I-HIRES - , Gemini-North-NIRI - , Gemini-South-Zorro - , Palomar - , SOAR - , LCOGT - , NGTS - , El Sauce - , PEST - , MuSCAT2. - \n\nSoftware: Astropy (Astropy Collaboration et al. 2013, 2018), radvel (Fulton et al. 2018), emcee (Foreman-Mackey et al. 2013), Spectroscopy Made Easy (Valenti & Piskunov 1996; Piskunov & Valenti 2017), SpecMatch Synth (Petigura 2015), SpecMatch-Emp (Yee et al. 2017), isoclassify (Huber et al. 2017), AstroImageJ (Collins et al. 2017), lightkurve (Lightkurve Collaboration et al. 2018), spock (Tamayo et al. 2020), kiauhoku (Claytor et al. 2020).", revision_no = "26", abstract = "We report the discovery of TOI-561, a multiplanet system in the galactic thick disk that contains a rocky, ultra-short-period planet. This bright (V = 10.2) star hosts three small transiting planets identified in photometry from the NASA TESS mission: TOI-561 b (TOI-561.02, P = 0.44 days, R_p = 1.45 ± 0.11 R_⊕), c (TOI-561.01, P = 10.8 days, R_p = 2.90 ± 0.13 R_⊕), and d (TOI-561.03, P = 16.3 days, R_p = 2.32 ± 0.16 R_⊕). The star is chemically ([Fe/H] = −0.41 ± 0.05, [α/Fe] = +0.23 ± 0.05) and kinematically consistent with the galactic thick-disk population, making TOI-561 one of the oldest (10 ± 3 Gyr) and most metal-poor planetary systems discovered yet. We dynamically confirm planets b and c with radial velocities from the W. M. Keck Observatory High Resolution Echelle Spectrometer. Planet b has a mass and density of 3.2 ± 0.8 M_⊕ and 5.5^(+2.0)_(-1.6) g cm⁻³, consistent with a rocky composition. Its lower-than-average density is consistent with an iron-poor composition, although an Earth-like iron-to-silicates ratio is not ruled out. Planet c is 7.0 ± 2.3 M_⊕ and 1.6 ± 0.6 g cm⁻³, consistent with an interior rocky core overlaid with a low-mass volatile envelope. Several attributes of the photometry for planet d (which we did not detect dynamically) complicate the analysis, but we vet the planet with high-contrast imaging, ground-based photometric follow-up, and radial velocities. TOI-561 b is the first rocky world around a galactic thick-disk star confirmed with radial velocities and one of the best rocky planets for thermal emission studies.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/107500, title ="Spiral Arm Pattern Motion in the SAO 206462 Protoplanetary Disk", author = "Xie, Chengyan and Ren, Bin", journal = "Astrophysical Journal Letters", volume = "906", number = "2", pages = "Art. No. L9", month = "January", year = "2021", doi = "10.3847/2041-8213/abd241", issn = "2041-8213", url = "https://resolver.caltech.edu/CaltechAUTHORS:20210114-164620409", note = "© 2021. The American Astronomical Society. \n\nReceived 2020 November 3; revised 2020 December 7; accepted 2020 December 8; published 2021 January 11. \n\nWe thank the anonymous referee for suggestions that increased the clarity and robustness of this Letter, and Jaehan Bae for useful discussions. T.F. and C.X. are supported by the National Key R&D Program of China No. 2017YFA0402600, project S202010384487 XMU Training Program of Innovation and Enterpreneurship for Undergraduate, and NSFC grants No. 11525312, 11890692. R.D. acknowledges financial support provided by the Natural Sciences and Engineering Research Council of Canada through a Discovery Grant, as well as the Alfred P. Sloan Foundation through a Sloan Research Fellowship. This research is partially supported by NASA ROSES XRP, award 80NSSC19K0294. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programs 095.C-0273 (A), 097.C-0702 (A), 097.C-0885 (A), and 297.C-5023 (A). Based on observations made with the NASA/ESA Hubble Space Telescope, 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. 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. \n\nFacilities: VLT:Melipal (SPHERE) - , Keck:II (NIRC2) - , HST (NICMOS). - \n\nSoftware: IRDAP (van Holstein et al. 2020), diskmap (Stolker et al. 2016b), scipy (Virtanen et al. 2020).", revision_no = "17", abstract = "Spiral arms have been observed in more than a dozen protoplanetary disks, yet the origin of nearly all systems is under debate. Multi-epoch monitoring of spiral arm morphology offers a dynamical way to distinguish two leading arm formation mechanisms: companion-driven and gravitational instability induction, since these mechanisms predict distinct motion patterns. By analyzing multi-epoch J-band observations of the SAO 206462 system using the SPHERE instrument on the Very Large Telescope in 2015 and 2016, we measure the pattern motion for its two prominent spiral arms in polarized light. On one hand, if both arms are comoving, they can be driven by a planet at 86₋₁₃⁺¹⁸ au on a circular orbit, with gravitational instability motion ruled out. On the other hand, they can be driven by two planets at 120₋₃₀⁺³⁰ au and 49₋₅⁺⁶ au, offering tentative evidence (3.0σ) that the two spirals are moving independently. The independent arm motion is possibly supported by our analysis of a re-reduction of archival observations using the NICMOS instrument on board the Hubble Space Telescope (HST) in 1998 and 2005, yet artifacts including shadows can manifest spurious arm motion in HST observations. We expect future re-observations to better constrain the motion mechanism for the SAO 206462 spiral arms.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/107337, title ="A Diversity of Wave-driven Presupernova Outbursts", author = "Wu, Samantha and Fuller, Jim", journal = "Astrophysical Journal", volume = "906", number = "1", pages = "Art. No. 3", month = "January", year = "2021", doi = "10.3847/1538-4357/abc87c", issn = "1538-4357", url = "https://resolver.caltech.edu/CaltechAUTHORS:20210106-102309010", note = "© 2020 The American Astronomical Society. \n\nReceived 2020 October 6; revised 2020 November 4; accepted 2020 November 5; published 2020 December 29. \n\nThis work was partially supported by NASA grants HST-AR-15021.001-A and 80NSSC18K1017. J.F. acknowledges support from an Innovator Grant from The Rose Hills Foundation, and the Sloan Foundation through grant FG-2018-10515.", revision_no = "16", abstract = "Many core-collapse supernova (SN) progenitors show indications of enhanced pre-SN mass loss and outbursts, some of which could be powered by wave energy transport within the progenitor star. Depending on the star's structure, convectively excited waves driven by late-stage nuclear burning can carry substantial energy from the core to the envelope, where the wave energy is dissipated as heat. We examine the process of wave energy transport in single-star SNe progenitors with masses between 11 and 50 M_⊙. Using MESA stellar evolution simulations, we evolve stars until core collapse and calculate the wave power produced and transmitted to the stars' envelopes. These models improve upon prior efforts by incorporating a more realistic wave spectrum and nonlinear damping effects, reducing our wave-heating estimates by ~1 order of magnitude compared to prior work. We find that waves excited during oxygen/neon burning typically transmit ~10⁴⁶–10⁴⁷ erg of energy at 0.1–10 yr before core collapse in typical (M < 30 M_⊙) SN progenitors. High-mass progenitors can often transmit ~10⁴⁷–10⁴⁸ erg of energy during oxygen/neon burning, but this tends to occur later, at about 0.01–0.1 yr before core collapse. Pre-SN outbursts may be most pronounced in low-mass SN progenitors (M ≾ 12 M_⊙) undergoing semidegenerate neon ignition and in high-mass progenitors (M ≳ 30 M_⊙) exhibiting convective shell mergers.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/104434, title ="Optical follow-up of the neutron star–black hole mergers S200105ae and S200115j", author = "Anand, Shreya and Coughlin, Michael W.", journal = "Nature Astronomy", volume = "5", number = "1", pages = "46-53", month = "January", year = "2021", doi = "10.1038/s41550-020-1183-3", issn = "2397-3366", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200717-162631605", note = "© 2020 Nature Publishing Group. \n\nReceived 14 April 2020; Accepted 20 July 2020; Published 14 September 2020. \n\nThis work was supported by the GROWTH (Global Relay of Observatories Watching Transients Happen) project funded by the National Science Foundation under PIRE grant no. 1545949. GROWTH is a collaborative project among California Institute of Technology (USA), University of Maryland College Park (USA), University of Wisconsin Milwaukee (USA), Texas Tech University (USA), San Diego State University (USA), University of Washington (USA), Los Alamos National Laboratory (USA), Tokyo Institute of Technology (Japan), National Central University (Taiwan), Indian Institute of Astrophysics (India), Indian Institute of Technology Bombay (India), Weizmann Institute of Science (Israel), The Oskar Klein Centre at Stockholm University (Sweden), Humboldt University (Germany), Liverpool John Moores University (UK) and University of Sydney (Australia). This work was based on observations obtained with the 48-inch Samuel Oschin Telescope and the 60-inch Telescope at the Palomar Observatory as part of the ZTF project. ZTF is supported by the National Science Foundation under grant no. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington (UW), Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee and Lawrence Berkeley National Laboratories. Operations are conducted by Caltech Optical Observatories, IPAC, and UW. The work is partly based on the observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias, in the island of La Palma. The KPED team (M.W.C., R.G.D., D.A.D., M.F., S.R.K., E.S. and R.R.) thanks the National Science Foundation and the National Optical Astronomical Observatory for making the Kitt Peak 2.1-m telescope available. We thank the observatory staff at Kitt Peak for their efforts to assist Robo-AO KP operations. The KPED team thanks the National Science Foundation, the National Optical Astronomical Observatory, the Caltech Space Innovation Council and the Murty family for support in the building and operation of KPED. In addition, they thank the CHIMERA project for use of the Electron Multiplying CCD (EMCCD). SED Machine is based upon work supported by the National Science Foundation under grant no. 1106171 The ZTF forced-photometry service was funded under the Heising-Simons Foundation grant #12540303 (PI: Graham). M.W.C. acknowledges support from the National Science Foundation with grant no. PHY-2010970. S.A. gratefully acknowledges support from a GROWTH PIRE grant (1545949). Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. E.C.K. acknowledges support from the G.R.E.A.T. research environment and the Wenner-Gren Foundations. F.F. gratefully acknowledges support from NASA through grant 80NSSC18K0565, from the NSF through grant PHY-1806278, and from the DOE through CAREER grant DE-SC0020435. \n\nData availability: The data that support the plots within this paper and other findings of this study are available from the corresponding authors on reasonable request. \n\nCode availability: The code (primarily in python) used to produce the figures is available from the corresponding authors on reasonable request. \n\nThese authors contributed equally: Shreya Anand, Michael W. Coughlin. \n\nAuthor Contributions: S.A. and M.W.C. were the primary authors of the manuscript. M.M.K. is the PI of GROWTH and the ZTF EM-GW programme. M.B., A.S.C. and F.F. led the theory and modelling. T.A., M.A., N.G., I.A. and L.P.S. support the development of the GROWTH TOO Marshal and the associated programme. T.A., R. Stein, J.S., S.B.C., V.Z.G., A.K.H.K., H.K., E.C.K., P.M. and S.R. contributed to candidate scanning, vetting and classification. E.C.B. leads the ZTF scheduler and associated interfacing with the TOO programme. B.B. interpreted the asteroid candidates. M.D.C.-G., A.J.C.-T., Y.H., R. Sánchez-Ramírez and A.F.V. provided GTC data and associated analysis. K.D. and M.J.H. provided P200 follow-up. R.G.D., D.A.D., M.F., S.R.K., E.S. and R.R. provided KPED data. M.R. and R.W. provided SEDM data. C.F., M.J.G., R.R.L., F.J.M., P.M, M.P., P.R., B.R., D.L.S., R. Smith, M.T.S. and R.W. are ZTF builders. All authors contributed to editing the manuscript. \n\nThe authors declare no competing interests. \n\nPeer review information: Nature Astronomy thanks Aaron Zimmerman and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.", revision_no = "133", abstract = "LIGO and Virgo’s third observing run revealed the first neutron star–black hole (NSBH) merger candidates in gravitational waves. These events are predicted to synthesize r-process elements creating optical/near-infrared ‘kilonova’ emission. The joint gravitational wave and electromagnetic detection of an NSBH merger could be used to constrain the equation of state of dense nuclear matter, and independently measure the local expansion rate of the Universe. Here, we present the optical follow-up and analysis of two of the only three high-significance NSBH merger candidates detected to date, S200105ae and S200115j, with the Zwicky Transient Facility. The Zwicky Transient Facility observed ~48% of S200105ae and ~22% of S200115j’s localization probabilities, with observations sensitive to kilonovae brighter than −17.5\u2009mag fading at 0.5\u2009mag\u2009d⁻¹ in the g- and r-bands; extensive searches and systematic follow-up of candidates did not yield a viable counterpart. We present state-of-the-art kilonova models tailored to NSBH systems that place constraints on the ejecta properties of these NSBH mergers. We show that with observed depths of apparent magnitude ~22\u2009mag, attainable in metre-class, wide-field-of-view survey instruments, strong constraints on ejecta mass are possible, with the potential to rule out low mass ratios, high black hole spins and large neutron star radii.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/105416, title ="Physical Parameters of the Multiplanet Systems HD 106315 and GJ 9827", author = "Kosiarek, Molly R. and Berardo, David A.", journal = "Astronomical Journal", volume = "161", number = "1", pages = "Art. No. 147", month = "January", year = "2021", doi = "10.3847/1538-3881/abca39", issn = "1538-3881", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200916-112905779", note = "© 2020 The American Astronomical Society. \n\nReceived 2020 September 7; revised 2020 November 9; accepted 2020 November 11; published 2020 December 31. \n\nBased on observations obtained at the W. M. Keck Observatory, which is operated jointly by the University of California and the California Institute of Technology. \n\nThis paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile. \n\nWe thank the anonymous reviewer for their time and helpful comments. \n\nM.R.K is supported by the NSF Graduate Research Fellowship, grant No. DGE 1339067. \n\nC.P. is supported by the Technologies for Exo-Planetary Science (TEPS) CREATE program and further acknowledges financial support by the Fonds de Recherche QuébécoisNature et Technologie (FRQNT; Québec). \n\nG.W.H. acknowledges long-term support from NASA, NSF, Tennessee State University, and the State of Tennessee through its Centers of Excellence program. \n\nL.M.W. is supported by the Beatrice Watson Parrent Fellowship and NASA ADAP grant 80NSSC19K0597. \n\nP.D. acknowledges support from a National Science Foundation Astronomy and Astrophysics Postdoctoral Fellowship under award AST-1903811. \n\nJ.M.A.M. gratefully acknowledges support from the National Science Foundation Graduate Research Fellowship Program under grant No. DGE-1842400. J.M.A.M. also thanks the LSSTC Data Science Fellowship Program, which is funded by LSSTC, NSF Cybertraining grant No. 1829740, the Brinson Foundation, and the Moore Foundation; his participation in the program has benefited this work. \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\nSome of the observations in the paper made use of the High-Resolution Imaging instrument Zorro. Zorro was funded by the NASA Exoplanet Exploration Program and built at the NASA Ames Research Center by Steve B. Howell, Nic Scott, Elliott P. Horch, and Emmett Quigley. Zorro is mounted on the Gemini South telescope of the international Gemini Observatory, a program of NSFs OIR Lab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. \n\nThis work is based in part on observations made with the Spitzer Space Telescope, which was operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. \n\nThis research has made use of the Exoplanet Follow-up Observing Program (ExoFOP), which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration. \n\nPart of the research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). \n\nThis work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. \n\nFacilities: Keck:I(HIRES) - KECK I Telescope, Magellan:Clay(PFS) - Magellan II Landon Clay Telescope, Spitzer - Spitzer Space Telescope satellite, APF - , TSU:AIT - , Gemini:South(Zorro). - \n\nSoftware: radvel (Fulton et al. 2018), batman (Kreidberg 2015), SpecMatch-Emp (Yee et al. 2017), isoclassify (Huber et al. 2017), spock (Tamayo et al. 2020), rebound (Rein & Liu 2011), numpy (van der Walt et al. 2011), astropy (Astropy Collaboration et al. 2013), emcee (Foreman-Mackey et al. 2013).", revision_no = "32", abstract = "HD 106315 and GJ 9827 are two bright, nearby stars that host multiple super-Earths and sub-Neptunes discovered by K2 that are well suited for atmospheric characterization. We refined the planets' ephemerides through Spitzer transits, enabling accurate transit prediction required for future atmospheric characterization through transmission spectroscopy. Through a multiyear high-cadence observing campaign with Keck/High Resolution Echelle Spectrometer and Magellan/Planet Finder Spectrograph, we improved the planets' mass measurements in anticipation of Hubble Space Telescope transmission spectroscopy. For GJ 9827, we modeled activity-induced radial velocity signals with a Gaussian process informed by the Calcium II H&K lines in order to more accurately model the effect of stellar noise on our data. We measured planet masses of M_b = 4.87 ± 0.37 M_⊕, M_c = 1.92 ± 0.49 M_⊕, and M_d = 3.42 ± 0.62 M_⊕. For HD 106315, we found that such activity radial velocity decorrelation was not effective due to the reduced presence of spots and speculate that this may extend to other hot stars as well (T_(eff) > 6200 K). We measured planet masses of M_b = 10.5 ± 3.1 M_⊕ and M_c = 12.0 ± 3.8 M_⊕. We investigated all of the planets' compositions through comparison of their masses and radii to a range of interior models. GJ 9827 b and GJ 9827 c are both consistent with a 50/50 rock-iron composition, GJ 9827 d and HD 106315 b both require additional volatiles and are consistent with moderate amounts of water or hydrogen/helium, and HD 106315 c is consistent with a ~10% hydrogen/helium envelope surrounding an Earth-like rock and iron core.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/107501, title ="Probing the CGM of low-redshift dwarf galaxies using FIRE simulations", author = "Li, Fei and Rahman, Mubdi", journal = "Monthly Notices of the Royal Astronomical Society", volume = "500", number = "1", pages = "1038-1053", month = "January", year = "2021", doi = "10.1093/mnras/staa3322", issn = "0035-8711", url = "https://resolver.caltech.edu/CaltechAUTHORS:20210114-164620520", note = "© 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model) \n\nAccepted 2020 October 13. Received 2020 September 26; in original form 2020 June 10. \n\nWe thank Lauren Corlies for her help in using TRIDENT. FL thanks Gunjan Lakhlani for sharing the routines to calculate the dynamical time. We benefitted from discussions with Bili Dong and Maan H. Hani. The analysis on the FIRE simulation data were run on XSEDE computational resources (allocations TG-AST120025 and TG-AST120023) and on the CITA compute cluster Sunnyvale. This research was enabled in part by support provided by SciNet (http://www.scinet.utoronto.ca) and Compute Canada =\"http://www..computecanada.ca). Computations were performed on the Niagara supercomputer (Ponce et al. 2019; Loken et al. 2010) at the SciNet HPC Consortium. SciNet is funded by: the Canada Foundation for Innovation; the Government of Ontario; Ontario Research Fund - Research Excellence; and the University of Toronto. The data used in this work were, in part, hosted on facilities supported by the Scientific Computing Core at the Flatiron Institute, a division of the Simons Foundation. This work was performed in part at the Aspen Center for Physics, which is supported by National Science Foundation grant PHY-1607611. CAFG was supported by NSF through grants AST-1517491, AST-1715216, and CAREER award AST-1652522, by NASA through grant 17-ATP17-0067, by STScI through grants HST-GO-14681.011, HST-GO-14268.022-A, and HST-AR-14293.001-A, and by a Cottrell Scholar Award from the Research Corporation for Science Advancement. \n\nSoftware: SCIPY,3 NUMPY4 (van der Walt, Colbert & Varoquaux 2011), MATPLOTLIB5 (Hunter 2007), MPI4PY6 (Dalcín, Paz & Storti 2005), TRIDENT7 (Hummels et al. 2017), and YT8 (Turk et al. 2011). \n\nDATA AVAILABILITY. The data supporting the plots within this article are available on reasonable request to the corresponding author. A public version of the GIZMO code is available at http://www.tapir.caltech.edu/phopkins/Site/GIZMO.html. Additional data including simulation snapshots, initial conditions, and derived data products are available at https://fire.northwestern.edu/data/.", revision_no = "14", abstract = "Observations of ultraviolet (UV) metal absorption lines have provided insight into the structure and composition of the circumgalactic medium (CGM) around galaxies. We compare these observations with the low-redshift (z ≤ 0.3) CGM around dwarf galaxies in high-resolution cosmological zoom-in runs in the FIRE-2 (Feedback In Realistic Environments) simulation suite. We select simulated galaxies that match the halo mass, stellar mass, and redshift of the observed samples. We produce absorption measurements using TRIDENT for UV transitions of C\u2009IV, O\u2009VI, Mg\u2009II, and Si\u2009III. The FIRE equivalent width (EW) distributions and covering fractions for the C\u2009IV ion are broadly consistent with observations inside 0.5R_(vir), but are underpredicted for O\u2009VI, Mg\u2009II, and Si\u2009III. The absorption strengths of the ions in the CGM are moderately correlated with the masses and star formation activity of the galaxies. The correlation strengths increase with the ionization potential of the ions. The structure and composition of the gas from the simulations exhibit three zones around dwarf galaxies characterized by distinct ion column densities: the discy interstellar medium, the inner CGM (the wind-dominated regime), and the outer CGM (the IGM accretion-dominated regime). We find that the outer CGM in the simulations is nearly but not quite supported by thermal pressure, so it is not in hydrostatic equilibrium, resulting in halo-scale bulk inflow and outflow motions. The net gas inflow rates are comparable to the star formation rate of the galaxy, but the bulk inflow and outflow rates are greater by an order of magnitude, with velocities comparable to the virial velocity of the halo. These roughly virial velocities (\u2060∼100 km s⁻¹\u2060) produce large EWs in the simulations. This supports a picture for dwarf galaxies in which the dynamics of the CGM at large scales are coupled to the small-scale star formation activity near the centre of their haloes.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/106968, title ="Transmission Spectroscopy for the Warm Sub-Neptune HD 3167c: Evidence for Molecular Absorption and a Possible High-metallicity Atmosphere", author = "Mikal-Evans, Thomas and Crossfield, Ian J. M.", journal = "Astronomical Journal", volume = "161", number = "1", pages = "Art. No. 18", month = "January", year = "2021", doi = "10.3847/1538-3881/abc874", issn = "1538-3881", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201208-105039183", note = "© 2020. The American Astronomical Society. \n\nReceived 2020 July 31; revised 2020 October 19; accepted 2020 November 5; published 2020 December 7. \n\nThe authors are grateful to the referee for constructive feedback that improved the quality of the manuscript. Support for HST program GO-15333 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. This work is based in part on observations made with the Spitzer Space Telescope, which was operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. Some of the data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX13AC07G and by other grants and contracts. P.M. acknowledges support from the European Research Council under the European Union's Horizon 2020 research and innovation program under grant agreement No. 832428. D.D. acknowledges support from the TESS Guest Investigator Program grant 80NSSC19K1727 and NASA Exoplanet Research Program grant 18-2XRP18 2-0136. M.R.K. is supported by the NSF Graduate Research Fellowship, grant No. DGE 1339067. \n\nFacilities: HST(WFC3) - Hubble Space Telescope satellite, Spitzer(IRAC) - , Kepler(K2) - , Keck(HIRES). - \n\nSoftware: NumPy (van der Walt et al. 2011), SciPy (Virtanen et al. 2020), Matplotlib (Hunter 2007), emcee (Foreman-Mackey et al. 2013), batman (Kreidberg 2015), Astropy (Astropy Collaboration et al. 2013, 2018), pysynphot (STScI Development Team 2013), petitRadtrans (Mollière et al. 2019), PyMultinest (Buchner et al. 2014).", revision_no = "11", abstract = "We present a transmission spectrum for the warm (500−600 K) sub-Neptune HD 3167c obtained using the Hubble Space Telescope Wide Field Camera 3 infrared spectrograph. We combine these data, which span the 1.125–1.643 μm wavelength range, with broadband transit measurements made using Kepler/K2 (0.6–0.9 μm) and Spitzer/IRAC (4–5 μm). We find evidence for absorption by at least one of H₂O, HCN, CO₂, and CH₄ (Bayes factor 7.4; 2.5σ significance), although the data precision does not allow us to unambiguously discriminate between these molecules. The transmission spectrum rules out cloud-free hydrogen-dominated atmospheres with metallicities ≤100× solar at >5.8σ confidence. In contrast, good agreement with the data is obtained for cloud-free models assuming metallicities >700× solar. However, for retrieval analyses that include the effect of clouds, a much broader range of metallicities (including subsolar) is consistent with the data, due to the degeneracy with cloud-top pressure. Self-consistent chemistry models that account for photochemistry and vertical mixing are presented for the atmosphere of HD 3167c. The predictions of these models are broadly consistent with our abundance constraints, although this is primarily due to the large uncertainties on the latter. Interior structure models suggest that the core mass fraction is >40%, independent of a rock or water core composition, and independent of atmospheric envelope metallicity up to 1000× solar. We also report abundance measurements for 15 elements in the host star, showing that it has a very nearly solar composition.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/107276, title ="Characterizing the Circumgalactic Medium of the Lowest-mass Galaxies: A Case Study of IC 1613", author = "Zheng, Yong and Emerick, Andrew", journal = "Astrophysical Journal", volume = "905", number = "2", pages = "Art. No. 133", month = "December", year = "2020", doi = "10.3847/1538-4357/abc875", issn = "1538-4357", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201224-085807319", 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 2020 August 11; revised 2020 October 26; accepted 2020 November 6; published 2020 December 22. \n\nWe thank R. Bordoloi for sharing his python code of escape velocity calculation, E. Patel for discussing the projection effect between the Magellanic System and the LG galaxies using hydrodynamic simulations and HST/Gaia proper motion measurements, and D. Weisz for discussing many aspects of this paper and for his great support as a faculty mentor to Y.Z. at Miller Institute at UC Berkeley. We also thank A. Fox and P. Richter for helpful discussion on the manuscript. Y.Z. acknowledges support from the Miller Institute for Basic Research in Science. Support for Program number HST-GO-15156 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. This material is based upon work supported by the National Science Foundation under grant No. AST-1847909. E.N.K. gratefully acknowledges support from a Cottrell Scholar award administered by the Research Corporation for Science Advancement. This research has made use of the HSLA database, developed and maintained at STScI, Baltimore, USA. \n\nFacilities: Hubble Space Telescope/Cosmic Origins Spectrograph - , Mikulski Archive for Space Telescopes (MAST). - \n\nSoftware: Astropy (The Astropy Collaboration et al. 2018), Numpy (Harris et al. 2020), Matplotlib (Hunter 2007), CLOUDY (Ferland et al. 2017), IDL, the gala package (Price-Whelan et al. 2017).", revision_no = "16", abstract = "Using 10 sight lines observed with the Hubble Space Telescope/Cosmic Origins Spectrograph, we study the circumgalactic medium (CGM) and outflows of IC 1613, which is a low-mass (M_* ~ 10⁸ M_⊙), dwarf irregular galaxy on the outskirts of the Local Group. Among the sight lines, four are pointed toward UV-bright stars in IC 1613, and the other six sight lines are background QSOs at impact parameters from 6 kpc (<0.1R_(200)) to 61 kpc (0.6R_(200)). We detect a number of Si ii, Si iii, Si iv, C ii, and C iv absorbers, most of which have velocities less than the escape velocity of IC 1613 and thus are gravitationally bound. The line strengths of these ion absorbers are consistent with the CGM absorbers detected in dwarf galaxies at low redshifts. Assuming that Si ii, Si iii, and Si iv comprise nearly 100% of the total silicon, we find 3% (~8 × 10³ M_⊙), 2% (~7 × 10³ M_⊙), and 32%–42% [~(1.0–1.3) × 10⁵ M_⊙] of the silicon mass in the stars, interstellar medium, and within 0.6R_(200) of the CGM of IC 1613. We also estimate the metal outflow rate to be Ṁ_(out,Z) ⩾ 1.1 x 10⁻⁵ M_⊙ yr⁻¹ and the instantaneous metal mass loading factor to be η_Z ≥ 0.004, which are in broad agreement with available observation and simulation values. This work is the first time a dwarf galaxy of such low mass is probed by a number of both QSO and stellar sight lines, and it shows that the CGM of low-mass, gas-rich galaxies can be a large reservoir enriched with metals from past and ongoing outflows.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/105068, title ="Kilonova Luminosity Function Constraints Based on Zwicky Transient Facility Searches for 13 Neutron Star Merger Triggers during O3", author = "Kasliwal, Mansi M. and Anand, Shreya", journal = "Astrophysical Journal", volume = "905", number = "2", pages = "Art. No. 145", month = "December", year = "2020", doi = "10.3847/1538-4357/abc335", issn = "1538-4357", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200824-085517593", note = "© 2020. The American Astronomical Society. \n\nReceived 2020 June 19; revised 2020 October 19; accepted 2020 October 19; published 2020 December 22. \n\nThis work was supported by the Global Relay of Observatories Watching Transients Happen (GROWTH) project, funded by the National Science Foundation under PIRE grant No. 1545949. GROWTH is a collaborative project among the California Institute of Technology (USA), University of Maryland College Park (USA), University of Wisconsin Milwaukee (USA), Texas Tech University (USA), San Diego State University (USA), University of Washington (USA), Los Alamos National Laboratory (USA), Tokyo Institute of Technology (Japan), National Central University (Taiwan), Indian Institute of Astrophysics (India), Indian Institute of Technology Bombay (India), Weizmann Institute of Science (Israel), The Oskar Klein Centre at Stockholm University (Sweden), Humboldt University (Germany), Liverpool John Moores University (UK), and University of Sydney (Australia). Based on observations obtained with the Samuel Oschin Telescope 48 inch and the 60 inch telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. The ZTF is supported by the National Science Foundation under grant No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. Operations are conducted by COO, IPAC, and UW. The ZTF forced photometry service was funded under Heising-Simons Foundation grant No. 12540303 (PI: Graham). The SED Machine is based upon work supported by the National Science Foundation under grant No. 1106171. \n\nThe GROWTH-India telescope is a 70 cm telescope with a 0.7° field of view, set up by the Indian Institute of Astrophysics and the Indian Institute of Technology Bombay with support from the Indo-US Science and Technology Forum (IUSSTF) and the Science and Engineering Research Board (SERB) of the Department of Science and Technology (DST), Government of India (https://sites.google.com/view/growthindia/). It is located at the Indian Astronomical Observatory (Hanle), operated by the Indian Institute of Astrophysics (IIA). The GROWTH-India project is supported by SERB and administered by IUSSTF under grant No. IUSSTF/PIRE Program/GROWTH/2015-16. This research has made use of the VizieR catalog access tool, CDS, Strasbourg, France (doi: 10.26093/cds/vizier). The original description of the VizieR service was published in A&AS 143, 23. These results made use of the Lowell Discovery Telescope (LDT) at Lowell Observatory. Lowell is a private, nonprofit institution dedicated to astrophysical research and public appreciation of astronomy and operates the LDT in partnership with Boston University, the University of Maryland, the University of Toledo, Northern Arizona University, and Yale University. The Large Monolithic Imager was built by Lowell Observatory using funds provided by the National Science Foundation (AST-1005313). The upgrade of the DeVeny optical spectrograph has been funded by a generous grant from John and Ginger Giovale and a grant from the Mt. Cuba Astronomical Foundation. The KPED team thanks the National Science Foundation and the National Optical Astronomical Observatory for making the Kitt Peak 2.1 m telescope available. We thank the observatory staff at Kitt Peak for their efforts to assist Robo-AO KP operations. The KPED team thanks the National Science Foundation, the National Optical Astronomical Observatory, the Caltech Space Innovation Council, and the Murty family for support in the building and operation of KPED. In addition, they thank the CHIMERA project for use of the Electron Multiplying CCD (EMCCD). The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council. Some spectroscopic observations were obtained with the Southern African Large Telescope (SALT). The Photometric Redshifts for the Legacy Surveys (PRLS) catalog used in this paper was produced thanks to funding from the U.S. Department of Energy Office of Science, Office of High Energy Physics, via grant DE-SC0007914. This publication has made use of data collected at Lulin Observatory, partly supported by MoST grant 108-2112-M-008-001. Based on observations made with the Gran Telescopio Canarias (GTC), installed at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias on the island of La Palma. \n\nM.M.K. acknowledges generous support from the David and Lucille Packard Foundation. M.W.C. acknowledges support from the National Science Foundation with grant No. PHY-2010970. A.G. and J.S. acknowledge support from the Knut and Alice Wallenberg Foundation and GREAT research environment grant 2016-06012, funded by the Swedish Research Council. Some of the work by D.A.P. was performed at the Aspen Center for Physics, which is supported by National Science Foundation grant PHY-1607611. D.A.P. was partially supported by a grant from the Simons Foundation. H.K. thanks the LSSTC Data Science Fellowship Program, which is funded by LSSTC, NSF Cybertraining Grant 1829740, the Brinson Foundation, and the Moore Foundation; his participation in the program has benefited this work. This work has been supported by the Spanish Science Ministry Centro de Excelencia Severo Ochoa Program under grant SEV-2017-0709. A.J.C.T. acknowledges support from the Junta de Andalucía (Project P07-TIC-03094) and Spanish Ministry Projects AYA2012-39727-C03-01, AYA2015-71718R, and PID2019-109974RB-I00. V.A.F. was supported by grant RFBR 19-02-00432. I.A. acknowledges support by a Ramón y Cajal grant (RYC-2013-14511) of the Ministerio de Ciencia, Innovación, y Universidades (MICIU) of Spain. He also acknowledges financial support from MCIU through grant AYA2016-80889-P. A.A.M. is funded by the Large Synoptic Survey Telescope Corporation, the Brinson Foundation, and the Moore Foundation in support of the LSSTC Data Science Fellowship Program; he also receives support as a CIERA Fellow by the CIERA Postdoctoral Fellowship Program (Center for Interdisciplinary Exploration and Research in Astrophysics, Northwestern University). A.C. acknowledges support from the National Science Foundation with grant No. 1907975. W.-H.I., A.K., K.-L.L., C.-C.N., A.P., H.T., and P.-C.Y. acknowledge support from Ministry of Science and Technology (MoST) Taiwan grants 104-2923-M-008-004-MY5, 107-2119-M-008-012, 108-2628-M-007-005-RSP, and 108-2112-M-007-025-MY3. D.D. is supported by an Australian Government Research Training Program Scholarship. S.A. is supported by the GROWTH project, funded by the National Science Foundation under PIRE grant No. 1545949. A.S.C. is supported by GREAT research environment grant 2016-06012, funded by the Swedish Research Council. E.C.K. acknowledges support from the G.R.E.A.T. research environment and the Wenner-Gren Foundations. A.J.C.T. is thankful for fruitful discussions with J. Cepa, E. Fernández-García, J. A. Font, S. Jeong, A. Martín-Carrillo, A. M. Sintes, and S. Sokolov. D.A.H.B. acknowledges research support from the National Research Foundation of South Africa. S.B.P. and V.B. acknowledge BRICS grant No. \"DST/IMRCD/BRICS/PilotCall1/ProFCheap/2017(G)\" for part of the present work. J.S.B. was partially supported by a Gordon and Betty Moore Foundation Data-Driven Discovery grant and a grant from the National Science Foundation, \"Conceptualization of a Scalable Cyberinfrastructure Center for Multimessenger Astrophysics.\"", revision_no = "63", abstract = "We present a systematic search for optical counterparts to 13 gravitational wave (GW) triggers involving at least one neutron star during LIGO/Virgo's third observing run (O3). We searched binary neutron star (BNS) and neutron star black hole (NSBH) merger localizations with the Zwicky Transient Facility (ZTF) and undertook follow-up with the Global Relay of Observatories Watching Transients Happen (GROWTH) collaboration. The GW triggers had a median localization area of 4480 deg², a median distance of 267 Mpc, and false-alarm rates ranging from 1.5 to 10⁻²⁵ yr⁻¹. The ZTF coverage in the g and r bands had a median enclosed probability of 39%, median depth of 20.8 mag, and median time lag between merger and the start of observations of 1.5 hr. The O3 follow-up by the GROWTH team comprised 340 UltraViolet/Optical/InfraRed (UVOIR) photometric points, 64 OIR spectra, and three radio images using 17 different telescopes. We find no promising kilonovae (radioactivity-powered counterparts), and we show how to convert the upper limits to constrain the underlying kilonova luminosity function. Initially, we assume that all GW triggers are bona fide astrophysical events regardless of false-alarm rate and that kilonovae accompanying BNS and NSBH mergers are drawn from a common population; later, we relax these assumptions. Assuming that all kilonovae are at least as luminous as the discovery magnitude of GW170817 (−16.1 mag), we calculate that our joint probability of detecting zero kilonovae is only 4.2%. If we assume that all kilonovae are brighter than −16.6 mag (the extrapolated peak magnitude of GW170817) and fade at a rate of 1 mag day⁻¹ (similar to GW170817), the joint probability of zero detections is 7%. If we separate the NSBH and BNS populations based on the online classifications, the joint probability of zero detections, assuming all kilonovae are brighter than −16.6 mag, is 9.7% for NSBH and 7.9% for BNS mergers. Moreover, no more than <57% (<89%) of putative kilonovae could be brighter than −16.6 mag assuming flat evolution (fading by 1 mag day⁻¹) at the 90% confidence level. If we further take into account the online terrestrial probability for each GW trigger, we find that no more than <68% of putative kilonovae could be brighter than −16.6 mag. Comparing to model grids, we find that some kilonovae must have M_(ej) < 0.03 M_⊙, X_(lan) > 10⁻⁴, or φ > 30° to be consistent with our limits. We look forward to searches in the fourth GW observing run; even 17 neutron star mergers with only 50% coverage to a depth of −16 mag would constrain the maximum fraction of bright kilonovae to <25%.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/106137, title ="Multiwavelength Radio Observations of Two Repeating Fast Radio Burst Sources: FRB 121102 and FRB 180916.J0158+65", author = "Pearlman, Aaron B. and Majid, Walid A.", journal = "Astrophysical Journal Letters", volume = "905", number = "2", pages = "Art. No. L27", month = "December", year = "2020", doi = "10.3847/2041-8213/abca31", issn = "2041-8213", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201019-093428722", note = "© 2020 The American Astronomical Society. \n\nReceived 2020 September 28; revised 2020 November 11; accepted 2020 November 13; published 2020 December 21. \n\nWe thank Professor Vicky Kaspi and the CHIME/FRB collaboration for their support of these observations and for providing the CHIME/FRB data used in Figure 3. We also thank the reviewer for valuable comments and suggestions. \n\nA.B.P. acknowledges support by the Department of Defense (DoD) through the National Defense Science and Engineering Graduate (NDSEG) Fellowship Program and by the National Science Foundation (NSF) Graduate Research Fellowship under Grant No. DGE-1144469. J.W.T.H. acknowledges funding from an NWO Vici fellowship. \n\nWe thank the Jet Propulsion Laboratory's Spontaneous Concept Research and Technology Development program for supporting this work. We also thank Dr. Stephen Lichten for providing programmatic support. In addition, we are grateful to the DSN scheduling team (Hernan Diaz, George Martinez, and Carleen Ward) and the GDSCC and MDSCC operations staff for scheduling and carrying out these observations. \n\nA portion of this research was performed at the Jet Propulsion Laboratory, California Institute of Technology and the Caltech campus, under a Research and Technology Development Grant through a contract with the National Aeronautics and Space Administration. U.S. government sponsorship is acknowledged.", revision_no = "20", abstract = "The spectra of fast radio bursts (FRBs) encode valuable information about the source's local environment, underlying emission mechanism(s), and the intervening media along the line of sight. We present results from a long-term multiwavelength radio monitoring campaign of two repeating FRB sources, FRB 121102 and FRB 180916.J0158+65, with the NASA Deep Space Network (DSN) 70 m radio telescopes (DSS-63 and DSS-14). The observations of FRB 121102 were performed simultaneously at 2.3 and 8.4 GHz, and spanned a total of 27.3 hr between 2019 September 19 and 2020 February 11. We detected two radio bursts in the 2.3 GHz frequency band from FRB 121102, but no evidence of radio emission was found at 8.4 GHz during any of our observations. We observed FRB 180916.J0158+65 simultaneously at 2.3 and 8.4 GHz, and also separately in the 1.5 GHz frequency band, for a total of 101.8 hr between 2019 September 19 and 2020 May 14. Our observations of FRB 180916.J0158+65 spanned multiple activity cycles during which the source was known to be active and covered a wide range of activity phases. Several of our observations occurred during times when bursts were detected from the source between 400 and 800 MHz with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) radio telescope. However, no radio bursts were detected from FRB 180916.J0158+65 at any of the frequencies used during our observations with the DSN radio telescopes. We find that FRB 180916.J0158+65's apparent activity is strongly frequency-dependent due to the narrowband nature of its radio bursts, which have less spectral occupancy at high radio frequencies (≳ 2 GHz). We also find that fewer or fainter bursts are emitted from the source at high radio frequencies. We discuss the implications of these results for possible progenitor models of repeating FRBs.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/105070, title ="ZTF20aajnksq (AT 2020blt): A Fast Optical Transient at z ≈ 2.9 with No Detected Gamma-Ray Burst Counterpart", author = "Ho, Anna Y. Q. and Perley, Daniel A.", journal = "Astrophysical Journal", volume = "905", number = "2", pages = "Art. No. 98", month = "December", year = "2020", doi = "10.3847/1538-4357/abc34d", issn = "1538-4357", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200824-095838244", note = "© 2020 The American Astronomical Society. \n\nReceived 2020 June 18; revised 2020 October 15; accepted 2020 October 17; published 2020 December 17. \n\nIt is a pleasure to thank the anonymous referee for a thorough and thoughtful report that greatly improved the quality of the paper. A.Y.Q.H. would like to thank Udi Nakar for pointing out that dirty fireballs will have a longer rise time than clean fireballs, and Chris Bochenek and Vikram Ravi for useful discussions regarding scintillation of radio point sources. She would also like to thank Steve Schulze, Eran Ofek, and Avishay Gal-Yam, and David Kaplan for their detailed reading of the manuscript. \n\nA.Y.Q.H. and K.D. were supported by the GROWTH project funded by the National Science Foundation under PIRE grant No. 1545949. A.Y.Q.H. was also supported by the Miller Institute for Basic Research in Science at the University of California Berkeley. A. A. Miller is funded by the Large Synoptic Survey Telescope Corporation, the Brinson Foundation, and the Moore Foundation in support of the LSSTC Data Science Fellowship Program; he also receives support as a CIERA Fellow by the CIERA Postdoctoral Fellowship Program (Center for Interdisciplinary Exploration and Research in Astrophysics, Northwestern University). C.F. gratefully acknowledges support of his research by the Heising-Simons Foundation (#2018-0907). A. Goobar acknowledges support from the K & A Wallenberg Foundation, the Swedish Research Council (VR), and the GREAT research environment grant 2016-06012. \n\nBased on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. Z.T.F. is supported by the National Science Foundation under grant No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. Operations are conducted by COO, IPAC, and UW. SED Machine is based upon work supported by the National Science Foundation under grant No. 1106171. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester. Based on observations obtained at the international Gemini Observatory, a program of NSFs OIR Lab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation, on behalf of the Gemini Observatory partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnología e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). Gemini data were processed using the Gemini IRAF package and DRAGONS (Data Reduction for Astronomy from Gemini Observatory North and South). The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. We acknowledge the use of public data from the Swift data archive. 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. \n\nFacilities: Swift - Swift Gamma-Ray Burst Mission, EVLA - , VLA - , Liverpool:2 m - , PO:1.2 m - , PO:1.5 m, Keck:I (LRIS). - \n\nSoftware: CASA (McMullin et al. 2007), astropy (Astropy Collaboration et al. 2013, 2018), matplotlib (Hunter 2007), scipy (Virtanen et al. 2020), DRAGONS.", revision_no = "50", abstract = "We present ZTF20aajnksq (AT 2020blt), a fast-fading (Δr = 2.3 mag in Δt = 1.3 days) red (g − r ≈ 0.6 mag) and luminous (M_(1626 Å) = −25.9 mag) optical transient at z = 2.9 discovered by the Zwicky Transient Facility (ZTF). AT 2020blt shares several features in common with afterglows to long-duration gamma-ray bursts (GRBs): (1) an optical light curve well-described by a broken power law with a break at t_j = 1 d (observer frame); (2) a luminous (L_(0.3–10 KeV) = 10⁴⁶ erg s⁻¹) X-ray counterpart; and (3) luminous (L_(10 GHz) = 4 × 10³¹ erg s⁻¹ Hz⁻¹) radio emission. However, no GRB was detected in the 0.74 days between the last ZTF nondetection (r > 21.36 mag) and the first ZTF detection (r = 19.60 mag), with an upper limit on the isotropic-equivalent gamma-ray energy release of E_(γ,iso) < 7 × 10⁵² erg. AT 2020blt is thus the third afterglow-like transient discovered without a detected GRB counterpart (after PTF11agg and ZTF19abvizsw) and the second (after ZTF19abvizsw) with a redshift measurement. We conclude that the properties of AT 2020blt are consistent with a classical (initial Lorentz factor Γ₀ ≳ 100) on-axis GRB that was missed by high-energy satellites. Furthermore, by estimating the rate of transients with light curves similar to that of AT 2020blt in ZTF high-cadence data, we agree with previous results that there is no evidence for an afterglow-like phenomenon that is significantly more common than classical GRBs, such as dirty fireballs. We conclude by discussing the status and future of fast-transient searches in wide-field high-cadence optical surveys.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/105433, title ="A Systematic Search of Zwicky Transient Facility Data for Ultracompact Binary LISA-detectable Gravitational-wave Sources", author = "Burdge, Kevin B. and Prince, Thomas A.", journal = "Astrophysical Journal", volume = "905", number = "1", pages = "Art. No. 32", month = "December", year = "2020", doi = "10.3847/1538-4357/abc261", issn = "1538-4357", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200916-113006965", note = "© 2020. The American Astronomical Society. \n\nReceived 2020 September 4; revised 2020 October 13; accepted 2020 October 15; published 2020 December 9. \n\nK.B.B. thanks the National Aeronautics and Space Administration and the Heising-Simons Foundation for supporting his research. \n\nM.W.C. acknowledges support from the National Science Foundation with grant No. PHY-2010970. \n\nP.R.-G. acknowledges support from the State Research Agency (AEI) of the Spanish Ministry of Science, Innovation and Universities (MCIU), and the European Regional Development Fund (FEDER) under grant AYA2017–83383–P. \n\nV.S.D., ULTRACAM, and HiPERCAM are supported by STFC. \n\nThe research leading to these results has received funding from the European Research Council under the European Union's Horizon 2020 research and innovation program numbers 677706 (WD3D) and 340040 (HiPERCAM). \n\nThis work is based on observations obtained with the Samuel Oschin Telescope 48 inch and the 60 inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under grant No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. Operations are conducted by COO, IPAC, and UW. \n\nThis work is based on observations made with the Gran Telescopio Canarias (GTC) installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, in the island of La Palma. \n\nThis work is based on observations made at the European Southern Observatory New Technology Telescope (NTT), La Silla. \n\nThe KPED team thanks the National Science Foundation and the National Optical Astronomical Observatory for making the Kitt Peak 2.1 m telescope available. The KPED team thanks the National Science Foundation, the National Optical Astronomical Observatory, and the Murty family for support in the building and operation of KPED. In addition, they thank the CHIMERA project for use of the Electron Multiplying CCD (EMCCD). \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. 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. \n\nThis article is based on observations made in the Observatorios de Canarias del IAC with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group of Telescopes in the Observatorio del Roque de los Muchachos. \n\nThis research benefited from interactions at the ZTF Theory Network Meeting that were funded by the Gordon and Betty Moore Foundation through grant GBMF5076 and support from the National Science Foundation through PHY-1748958. \n\nFacilities: PO:1.2 m (ZTF) - , KPNO:2.1 m (KPED) - , NTT (ULTRACAM) - , Hale (CHIMERA - , DBSP) - , GTC (HiPERCAM) - , Keck:I (LRIS). -", revision_no = "24", abstract = "Using photometry collected with the Zwicky Transient Facility, we are conducting an ongoing survey for binary systems with short orbital periods (P_b < 1 hr) with the goal of identifying new gravitational-wave sources detectable by the upcoming Laser Interferometer Space Antenna (LISA). We present a sample of 15 binary systems discovered thus far, with orbital periods ranging from 6.91 to 56.35 minutes. Of the 15 systems, seven are eclipsing systems that do not show signs of significant mass transfer. Additionally, we have discovered two AM Canum Venaticorum systems and six systems exhibiting primarily ellipsoidal variations in their lightcurves. We present follow-up spectroscopy and high-speed photometry confirming the nature of these systems, estimates of their LISA signal-to-noise ratios, and a discussion of their physical characteristics.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/106389, title ="An 8.8 Minute Orbital Period Eclipsing Detached Double White Dwarf Binary", author = "Burdge, Kevin B. and Coughlin, Michael W.", journal = "Astrophysical Journal Letters", volume = "905", number = "1", pages = "Art. No. L7", month = "December", year = "2020", doi = "10.3847/2041-8213/abca91", issn = "2041-8213", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201103-093416233", note = "© 2020 The American Astronomical Society. \n\nReceived 2020 October 20; revised 2020 November 13; accepted 2020 November 13; published 2020 December 9. \n\nK.B.B. thanks the National Aeronautics and Space Administration and the Heising-Simons Foundation for supporting his research. K.B.B. also wishes to thank Andrew Tisdale for his generous contribution to this research effort. M.W.C. acknowledges support from the National Science Foundation with grant No. PHY-2010970. J.F. acknowledges support from an Innovator Grant from the Rose Hills Foundation and the Sloan Foundation through grant FG-2018-10515. T.R.M. was supported by the UK's Science and Technology Facilities Council through grant ST/T000406/1. We wish to thank the referee of this work for their excellent suggestions, which have considerably enhanced the quality of the work. \n\nBased on observations obtained with the Samuel Oschin Telescope 48 inch and the 60 inch telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. The ZTF is supported by the National Science Foundation under grant No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. Operations are conducted by the COO, IPAC, and UW. \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. 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. \n\nThe ZTF forced-photometry service was funded under Heising-Simons Foundation grant 12540303 (PI: Graham). \n\nFacilities: PO:1.2 m (ZTF) - , Hale (CHIMERA) - , Keck:I (LRIS) - , Swift (XRT and UVOT). - \n\nSoftware: Aplpy (Robitaille & Bressert 2012), Astropy (Astropy Collaboration et al. 2013), CUVARBASE (https://github.com/johnh2o2/cuvarbase), LCURVE (Copperwheat et al. 2010), Lpipe (Perley 2019), Multinest (Feroz et al. 2009), Numpy (van der Walt et al. 2011).", revision_no = "24", abstract = "We report the discovery of ZTF J2243+5242, an eclipsing double white dwarf binary with an orbital period of just 8.8 minutes, the second known eclipsing binary with an orbital period of less than 10 minutes. The system likely consists of two low-mass white dwarfs and will merge in approximately 400,000 yr to form either an isolated hot subdwarf or an R Coronae Borealis star. Like its 6.91 minute counterpart, ZTF J1539+5027, ZTF J2243+5242 will be among the strongest gravitational-wave sources detectable by the space-based gravitational-wave detector the Laser Space Interferometer Antenna (LISA) because its gravitational-wave frequency falls near the peak of LISA's sensitivity. Based on its estimated distance of d = 2425⁺¹⁰⁸₋₁₁₄ pc, LISA should detect the source within its first few months of operation and achieve a signal-to-noise ratio of 63 ± 7 after 4 yr. We find component masses of M_A = 0.323^(+0.065)_(-0.047) and M_B = 0.335^(+0.052)_(-0.054) M_⊙ , radii of R_A = 0.0298^(+0.0013)_(-0.0012) and R_B = 0.0275^(+0.0012)_(-0.0013) R_⊙, and effective temperatures of T_A = 26, 300⁺¹⁷⁰⁰₋₉₀₀ and T_B = 19, 200⁺¹⁵⁰⁰₋₉₀₀ K. We determine all of these properties and the distance to this system using only photometric measurements, demonstrating a feasible way to estimate parameters for the large population of optically faint (r > 21 m_(AB)) gravitational-wave sources that the Vera Rubin Observatory and LISA should identify.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/106980, title ="Fast Outflows in Hot Dust-obscured Galaxies Detected with Keck/NIRES", author = "Finnerty, Luke and Larson, Kirsten", journal = "Astrophysical Journal", volume = "905", number = "1", pages = "Art. No. 16", month = "December", year = "2020", doi = "10.3847/1538-4357/abc3bf", issn = "1538-4357", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201209-122138973", note = "© 2020. The American Astronomical Society. \n\nReceived 2020 August 7; revised 2020 October 12; accepted 2020 October 20; published 2020 December 8. \n\nWe thank the anonymous reviewer for helpful suggestions that improved this paper. 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 wish to acknowledge the critical importance of the current and recent Maunakea Observatories daycrew, technicians, telescope operators, computer support, and office staff employees, especially during the challenging times presented by the COVID-19 pandemic. Their expertise, ingenuity, and dedication is indispensable to the continued successful operation of these observatories. \n\nThis publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. \n\nD. S. M. was supported in part by a Leading Edge Fund from the Canadian Foundation for Innovation (project No. 30951) and a Discovery Grant (RGPIN-2019-06524) from the Natural Sciences and Engineering Research Council (NSERC) of Canada. D. S. M. is also grateful to the Dunlap Institute for Astronomy and Astrophysics at the University of Toronto for its contribution to the NIRES H2RG detector. T. D.-S. acknowledges support from the CASSACA and CONICYT fund CAS-CONICYT Call 2018. C.-W. Tsai was supported by a grant from the NSFC (No. 11973051). This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2017R1A6A3A04005158). \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\nFacility: Keck:II (NIRES). - \n\nSoftware: astropy (Astropy Collaboration et al. 2013, 2018).", revision_no = "10", abstract = "We present rest-frame optical spectroscopic observations of 24 Hot Dust-Obscured Galaxies (Hot DOGs) at redshifts 1.7–4.6 with KECK/NIRES. Our targets are selected, based on their extreme red colors, to be the highest-luminosity sources from the WISE infrared survey. In 20 sources with well-detected emission, we fit the key [O iii], Hβ, Hα, [N ii], and [S ii] diagnostic lines to constrain physical conditions. Of the 17 targets with a clear detection of the [O iii]λ5007 Å emission line, 15 display broad blueshifted and asymmetric line profiles, with widths ranging from 1000 to 8000 km s⁻¹ and blueshifts up to 3000 km s⁻¹. These kinematics provide strong evidence for the presence of massive ionized outflows of up to 8000 M_ ⊙ yr⁻¹, with a median of 150 M_ ⊙ yr⁻¹. As many as eight sources show optical emission line ratios consistent with vigorous star formation. Balmer-line star formation rates, uncorrected for reddening, range from 30 to 1300 M_ ⊙ yr⁻¹, with a median of 50 M_ ⊙ yr⁻¹. Estimates of the SFR from Spectral Energy Distribution fitting of mid- and far-infrared photometry suggest significantly higher values. We estimate the central black hole masses to be of order 10⁸⁻¹⁰ M_ ⊙, assuming the present-day M_(BH)-σ_★ relation. The bolometric luminosities and the estimated masses of the central black holes of these galaxies suggest that many of the active galactic nucleus-dominated Hot DOGs are accreting at or above their Eddington limit. The combination of ongoing star formation, massive outflows, and high Eddington ratios suggest Hot DOGs are a transitional phase in galaxy evolution.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/107093, title ="NuSTAR Survey of Obscured Swift/BAT-selected Active Galactic Nuclei. II. Median High-energy Cutoff in Seyfert II Hard X-Ray Spectra", author = "Baloković, M. and Harrison, F. A.", journal = "Astrophysical Journal", volume = "905", number = "1", pages = "Art. No. 41", month = "December", year = "2020", doi = "10.3847/1538-4357/abc342", issn = "1538-4357", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201215-141036856", note = "© 2020. The American Astronomical Society. \n\nReceived 2020 April 19; revised 2020 August 7; accepted 2020 August 25; published 2020 December 11. \n\nThe authors appreciate helpful suggestions from the anonymous referee, which helped to improve the clarity of the paper. \n\nM.B. acknowledges support from the YCAA Prize Postdoctoal Fellowship, the National Aeronautics and Space Administration (NASA) under the NASA Earth and Space Science Fellowship program (grant NNX14AQ07H), and support from the Black Hole Initiative at Harvard University, which is funded in part by the Gordon and Betty Moore Foundation (grant GBMF8273) and in part by the John Templeton Foundation. A.C. and G.M. acknowledge support from the ASI/INAF grant I/037/12/0 and the Caltech Kingsley fellowship program. A.A. acknowledges financial support from Ministry of Education Malaysia Fundamental Research Grant Scheme grant code FRGS/1/2019/STG02/UKM/02/7. P.B. acknowledges financial support from the STFC and the Czech Science Foundation project No. 19-05599Y. P.G. acknowledges support from the STFC and a UGC/UKIERI Thematic Partnership. \n\nWe have made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software and Calibration teams for support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the Space Science Data Center (SSDC; ASI, Italy) and the California Institute of Technology (USA). Part of this work is based on archival data, software, or online services provided by the SSDC. This research has made use of the High Energy Astrophysics Science Archive Research Center Online Service, provided by the NASA/Goddard Space Flight Center and NASA's Astrophysics Data System. \n\nFacilities: NuSTAR - The NuSTAR (Nuclear Spectroscopic Telescope Array) mission, Swift. - \n\nSoftware: Astropy (Astropy Collaboration et al. 2013, 2018), ASURV (Feigelson et al. 2014), Matplotlib (Hunter 2007), Xspec (Arnaud 1996).", revision_no = "15", abstract = "Broadband X-ray spectroscopy of the X-ray emission produced in the coronae of active galactic nuclei (AGNs) can provide important insights into the physical conditions very close to their central supermassive black holes. The temperature of the Comptonizing plasma that forms the corona is manifested through a high-energy cutoff that has been difficult to directly constrain even in the brightest AGN because it requires high-quality data at energies above 10 keV. In this paper we present a large collection of coronal cutoff constraints for obscured AGNs based on a sample of 130 AGNs selected in the hard X-ray band with Swift/BAT and observed nearly simultaneously with NuSTAR and Swift/XRT. We find that under a reasonable set of assumptions regarding partial constraints the median cutoff is well constrained to 290 ± 20 keV, where the uncertainty is statistical and given at the 68% confidence level. We investigate the sensitivity of this result to our assumptions and find that consideration of various known systematic uncertainties robustly places the median cutoff between 240 and 340 keV. The central 68% of the intrinsic cutoff distribution is found to be between about 140 and 500 keV, with estimated uncertainties of 20 and 100 keV, respectively. In comparison with the literature, we find no clear evidence that the cutoffs in obscured and unobscured AGNs are substantially different. Our analysis highlights the importance of carefully considering partial and potentially degenerate constraints on the coronal high-energy cutoff in AGNs.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/107122, title ="Quasars That Have Transitioned from Radio-quiet to Radio-loud on Decadal Timescales Revealed by VLASS and FIRST", author = "Nyland, Kristina and Dong, Dillon Z.", journal = "Astrophysical Journal", volume = "905", number = "1", pages = "Art. No. 74", month = "December", year = "2020", doi = "10.3847/1538-4357/abc341", issn = "0004-637X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201216-115150890", note = "© 2020. The American Astronomical Society. \n\nReceived 2020 August 17; revised 2020 October 14; accepted 2020 October 19; published 2020 December 15. \n\nWe thank the anonymous referee for providing us with helpful comments that have improved the quality of this work. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Basic research in radio astronomy at the U.S. Naval Research Laboratory is supported by 6.1 Base Funding. M.K.-B. acknowledges support from the \"National Science Centre, Poland\" under grant No. 2017/26/E/ST9/00216. \n\nFacility: VLA. - \n\nSoftware: Astropy (Astropy Collaboration et al. 2013), CASA (McMullin et al. 2007), Obit (Cotton 2008), and Montage (Jacob et al. 2010; Berriman & Good 2017).", revision_no = "12", abstract = "We have performed a search over 3440 deg² of Epoch 1 (2017–2019) of the Very Large Array Sky Survey to identify unobscured quasars in the optical (0.2 < z < 3.2) and obscured active galactic nuclei (AGNs) in the infrared that have brightened dramatically in the radio over the past one to two decades. These sources would have been previously classified as \"radio-quiet\" quasars based on upper limits from the Faint Images of the Radio Sky at Twenty cm survey (1993–2011), but they are now consistent with \"radio-loud\" quasars L_(3 GHz) = 10⁴⁰⁻⁴² erg s⁻¹. A quasi-simultaneous, multiband (~1–18 GHz) follow-up study of 14 sources with the VLA has revealed compact sources (<0.\"1 or <1 kpc) with peaked radio spectral shapes. The high-amplitude variability over decadal timescales at 1.5 GHz (100% to >2500%) but roughly steady fluxes over a few months at 3 GHz are inconsistent with extrinsic variability due to propagation effects, thus favoring an intrinsic origin. We conclude that our sources are powerful quasars hosting compact/young jets. This challenges the generally accepted idea that \"radio-loudness\" is a property of the quasar/AGN population that remains fixed on human timescales. Our study suggests that frequent episodes of short-lived AGN jets that do not necessarily grow to large scales may be common at high redshift. We speculate that intermittent but powerful jets on subgalactic scales could interact with the interstellar medium, possibly driving feedback capable of influencing galaxy evolution.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/103706, title ="The Zwicky Transient Facility Census of the Local Universe. I. Systematic Search for Calcium-rich Gap Transients Reveals Three Related Spectroscopic Subclasses", author = "De, Kishalay and Kasliwal, Mansi M.", journal = "Astrophysical Journal", volume = "905", number = "1", pages = "Art. No. 58", month = "December", year = "2020", doi = "10.3847/1538-4357/abb45c", issn = "1538-4357", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200604-151423784", note = "© 2020. The American Astronomical Society. \n\nReceived 2020 April 19; revised 2020 August 7; accepted 2020 August 25; published 2020 December 11. \n\nWe thank the anonymous referee for a careful reading of the manuscript that helped significantly improve its content. We thank H. Perets, K. Shen, E.S. Phinney, J. Fuller, D. Kasen, B. Margalit, and S. Schulze for valuable discussions during this work. We thank M. Coughlin, S. Anand, A. Sagues Carracedo, L. Rauch, and U. Feindt for several discussions on the use of simsurvey. \n\nThis work was supported by the GROWTH project funded by the National Science Foundation under Partnerships for International Research and Education (PIRE) grant no. 1545949. GROWTH is a collaborative project among Caltech (USA), University of Maryland College Park (USA), University of Wisconsin Milwaukee (USA), Texas Tech University (USA), San Diego State University (USA), University of Washington (USA), Los Alamos National Laboratory (USA), Tokyo Institute of Technology (Japan), National Central University (Taiwan), Indian Institute of Astrophysics (India), Indian Institute of Technology Bombay (India), Weizmann Institute of Science (Israel), The Oskar Klein Centre at Stockholm University (Sweden), Humboldt University (Germany), Liverpool John Moores University (UK), and University of Sydney (Australia). This research benefited from interactions at several ZTF Theory Network meetings, funded by the Gordon and Betty Moore Foundation through grant GBMF5076. M.M.K. acknowledges generous support from the David and Lucille Packard Foundation. \n\nBased on observations obtained with the Samuel Oschin Telescope 48 inch and the 60 inch Telescope at the Palomar Observatory as part of the ZTF project. ZTF is supported by the National Science Foundation under grant no. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Centre at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. Operations are conducted by COO, IPAC, and UW. SEDM is based upon work supported by the National Science Foundation under grant no. 1106171. The ZTF forced-photometry service was funded under Heising-Simons Foundation grant 12540303 (PI: Graham). Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among Caltech, 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. Based on observations made with NOT (operated by the Nordic Optical Telescope Scientific Association at Observatorio del Roque de los Muchachos, La Palma, Spain, of Instituto de Astrofisica de Canarias). \n\nA.G.Y.'s research is supported by the European Union via European Research Council grant no. 725161, the ISF GW Excellence Center, an IMOS space infrastructure grant, and BSF/Transformative and GIF grants, as well as The Benoziyo Endowment Fund for the Advancement of Science, the Deloro Institute for Advanced Research in Space and Optics, The Veronika A. Rabl Physics Discretionary Fund, Paul and Tina Gardner, Yeda-Sela, and the WIS–CIT joint research grant. A.G.Y. is a recipient of the Helen and Martin Kimmel Award for Innovative Investigation. A.Y.Q.H. is supported by a National Science Foundation Graduate Research Fellowship under grant no. DGE-1144469 and by the GROWTH project funded by the National Science Foundation under PIRE grant no. 1545949. R.L. is supported by a Marie Skłodowska-Curie Individual Fellowship within the Horizon 2020 EU Framework Programme for Research and Innovation (H2020-MSCA-IF-2017-794467). Foscgui is a graphic user interface aimed at extracting SN spectroscopy and photometry obtained with FOSC-like instruments. It was developed by E. Cappellaro. A package description can be found at http://sngroup.oapd.inaf.it/foscgui.html. \n\nFacilities: PO:1.2 m (ZTF) - , PO:1.5 m (SEDM) - , Hale (DBSP - , WaSP) - , NOT: ALFOSC - , THO: ALPY200 - , Keck:I (LRIS). - \n\nSoftware: astropy (Astropy Collaboration et al. 2013), matplotlib (Hunter 2007), scipy (Virtanen et al. 2020), pandas (McKinney 2010), SExtractor (Bertin & Arnouts 1996), scamp (Bertin 2006), SWarp (Bertin et al. 2002), PSFEx (Bertin 2011), pysedm (Rigault et al. 2019), pyraf-dbsp (Bellm & Sesar 2016), lpipe (Perley 2019), simsurvey (Feindt et al. 2019).", revision_no = "115", abstract = "Using the Zwicky Transient Facility alert stream, we are conducting a large spectroscopic campaign to construct a complete, volume-limited sample of transients brighter than 20 mag, and coincident within 100\" of galaxies in the Census of the Local Universe catalog. We describe the experiment design and spectroscopic completeness from the first 16 months of operations, which have classified 754 supernovae. We present results from a systematic search for calcium-rich gap transients in the sample of 22 low-luminosity (peak absolute magnitude M > −17), hydrogen-poor events found in the experiment. We report the detection of eight new events, and constrain their volumetric rate to ≳ 15% ± 5% of the SN Ia rate. Combining this sample with 10 previously known events, we find a likely continuum of spectroscopic properties ranging from events with SN Ia–like features (Ca-Ia objects) to those with SN Ib/c–like features (Ca-Ib/c objects) at peak light. Within the Ca-Ib/c events, we find two populations distinguished by their red (g − r ≈ 1.5 mag) or green (g - r ≈ 0.5 mag) colors at the r-band peak, wherein redder events show strong line blanketing features and slower light curves (similar to Ca-Ia objects), weaker He lines, and lower [Ca ii]/[O i] in the nebular phase. We find that all together the spectroscopic continuum, volumetric rates, and striking old environments are consistent with the explosive burning of He shells on low-mass white dwarfs. We suggest that Ca-Ia and red Ca-Ib/c objects arise from the double detonation of He shells, while green Ca-Ib/c objects are consistent with low-efficiency burning scenarios like detonations in low-density shells or deflagrations.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/98091, title ="A High-Order, Conservative Integrator with Local Time-Stepping", author = "Throwe, William and Teukolsky, Saul", journal = "SIAM Journal on Scientific Computing", volume = "42", number = "6", pages = "A3730-A3760", month = "December", year = "2020", doi = "10.1137/19M1292692", issn = "1064-8275", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190821-155551404", note = "© 2020 Society for Industrial and Applied Mathematics. \n\nSubmitted to the journal's Methods and Algorithms for Scientific Computing section October 11, 2019; accepted for publication (in revised form) September 21, 2020; published electronically December 1, 2020. \n\nThis work was partially supported by the Sherman Fairchild Foundation and by NSF through grants PHY-1606654 and ACI-1713678.", revision_no = "18", abstract = "We present a family of multistep integrators based on the Adams--Bashforth methods. These schemes can be constructed for arbitrary convergence order with arbitrary step size variation. The step size can differ between different subdomains of the system. It can also change with time within a given subdomain. The methods are linearly conservative, preserving a wide class of analytically constant quantities to numerical roundoff, even when numerical truncation error is significantly higher. These methods are intended for use in solving conservative PDEs in discontinuous Galerkin formulations or in finite-difference methods with compact stencils. A numerical test demonstrates these properties and shows that significant speed improvements over the standard Adams--Bashforth schemes can be obtained.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/105190, title ="Constraining the Kilonova Rate with Zwicky Transient Facility Searches Independent of Gravitational Wave and Short Gamma-Ray Burst Triggers", author = "Andreoni, Igor and Kool, Erik C.", journal = "Astrophysical Journal", volume = "904", number = "2", pages = "Art. No. 155", month = "December", year = "2020", doi = "10.3847/1538-4357/abbf4c", issn = "1538-4357", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200901-074328291", note = "© 2020. The American Astronomical Society. \n\nReceived 2020 July 31; revised 2020 September 22; accepted 2020 October 5; published 2020 November 30. \n\nWe thank the anonymous referee who helped us improve the quality of the manuscript. We thank P. Nugent for reviewing the manuscript and providing us with useful feedback. We thank D. Perley for useful discussion. Based on observations obtained with the Samuel Oschin 48 inch Telescope and the 60 inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project, a scientific collaboration among the California Institute of Technology, the Oskar Klein Centre, the Weizmann Institute of Science, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron, the University of Wisconsin-Milwaukee, and the TANGO Program of the University System of Taiwan. Further support is provided by the U.S. National Science Foundation under grant No. AST-1440341. This work was supported by the GROWTH (Global Relay of Observatories Watching Transients Happen) project funded by the National Science Foundation under PIRE grant No. 1545949. GROWTH is a collaborative project among California Institute of Technology (USA), University of Maryland College Park (USA), University of Wisconsin-Milwaukee (USA), Texas Tech University (USA), San Diego State University (USA), University of Washington (USA), Los Alamos National Laboratory (USA), Tokyo Institute of Technology (Japan), National Central University (Taiwan), Indian Institute of Astrophysics (India), Indian Institute of Technology Bombay (India), Weizmann Institute of Science (Israel), The Oskar Klein Centre at Stockholm University (Sweden), Humboldt University (Germany), Liverpool John Moores University (UK) and University of Sydney (Australia). E.C.K., A.S.C., and A.G. acknowledge support from the G.R.E.A.T research environment funded by Vetenskapsrådet, the Swedish Research Council, project number 2016-06012. E.C.K. also acknowledges support from The Wenner-Gren Foundations. M.W.C. acknowledges support from the National Science Foundation with grant No. PHY-2010970. D.L.K. is supported by NSF grant AST-1816492. M.M.K. acknowledges generous support from the David and Lucille Packard Foundation. We thank A. Miller for the star/galaxy classification code development for ZTF. This research has made use of the VizieR catalog access tool, CDS, Strasbourg, France (doi:10.26093/cds/vizier). The original description of the VizieR service was published in A&AS 143, 23. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. Software: Astropy (The Astropy Collaboration 2018), Pandas (pandas development team 2020), Matplotlib (Caswell et al. 2020), Kowalski (Duev et al. 2019), lpipe (Perley 2019), PostgreSQL22 , PyRAF DBSP data reduction pipeline (Bellm & Sesar 2016), ztfquery (Rigault 2018), SExtractor (Bertin & Arnouts 2010), ForcePhotZTF (Yao et al. 2019).", revision_no = "29", abstract = "The first binary neutron star merger, GW170817, was accompanied by a radioactivity-powered optical/infrared transient called a kilonova. To date, no compelling kilonova has been found in all-sky optical surveys, independently of short gamma-ray burst and gravitational-wave triggers. In this work, we searched the first 23 months of the Zwicky Transient Facility (ZTF) data stream for candidate kilonovae in the form of rapidly evolving transients. We combined ZTF alert queries with forced point-spread-function photometry and nightly flux stacking to increase our sensitivity to faint and fast transients. Automatic queries yielded >11,200 candidates, 24 of which passed quality checks and selection criteria based on a grid of kilonova models tailored for both binary neutron star and neutron star–black hole mergers. None of the candidates in our sample was deemed a possible kilonova after thorough vetting. The sources that passed our selection criteria are dominated by Galactic cataclysmic variables. We identified two fast transients at high Galactic latitude, one of which is the confirmed afterglow of long-duration GRB 190106A, the other is a possible cosmological afterglow. Using a survey simulation code, we constrained the kilonova rate for a range of models including top-hat, linearly decaying light curves, and synthetic light curves obtained with radiative transfer simulations. For prototypical GW170817-like kilonovae, we constrain the rate to be R < 1775 Gpc⁻³ yr⁻¹ (95% confidence). By assuming a population of kilonovae with the same geometry and composition of GW170817 observed under a uniform viewing angle distribution, we obtained a constraint on the rate of R < 4029 Gpc⁻³ yr⁻¹.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/106914, title ="Detection of 2–4 GHz Continuum Emission from ϵ Eridani", author = "Suresh, A. and Chatterjee, S.", journal = "Astrophysical Journal", volume = "904", number = "2", pages = "Art. No. 138", month = "December", year = "2020", doi = "10.3847/1538-4357/abc004", issn = "1538-4357", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201204-110357143", note = "© 2020. The American Astronomical Society. \n\nReceived 2020 August 14; revised 2020 October 2; accepted 2020 October 8; published 2020 November 27. \n\nAll authors thank J. Villadsen for initial conversations that motivated this work. A.S. thanks P. Nicholson and R. J. Jennings for useful thought-provoking discussions. A.S., S.C., and J.M.C. acknowledge support from the National Science Foundation (AAG 1815242). The VLA observations presented here were obtained as part of program VLA/19A−283, PI: A. Suresh. The VLA is operated by the National Radio Astronomy Observatory, a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. \n\nFacility: VLA. - \n\nSoftware: CASA (McMullin et al. 2007), Python 3 (http://www.python.org), Astropy (Price-Whelan et al. 2018), NumPy (van der Walt et al. 2011), Matplotlib (Hunter 2007), SciPy (Virtanen et al. 2020).", revision_no = "12", abstract = "The nearby star epsilon Eridani has been a frequent target of radio surveys for stellar emission and extraterrestrial intelligence. Using deep 2–4 GHz observations with the Very Large Array, we have uncovered a 29 μJy compact, steady continuum radio source coincident with epsilon Eridani to within 0.\"06 (⩽2σ; 0.2 au at the distance of the star). Combining our data with previous high-frequency continuum detections of epsilon Eridani, our observations reveal a spectral turnover at 6 GHz. We ascribe the 2–6 GHz emission to optically thick, thermal gyroresonance radiation from the stellar corona, with thermal free–free opacity likely becoming relevant at frequencies below 1 GHz. The steep spectral index (α ≃ 2) of the 2–6 GHz spectrum strongly disfavors its interpretation as stellar-wind-associated thermal bremsstrahlung (α ≃ 0.6). Attributing the entire observed 2–4 GHz flux density to thermal free–free wind emission, we thus derive a stringent upper limit of 3 × 10⁻¹¹ M_⊙ yr⁻¹ on the mass-loss rate from epsilon Eridani. Finally, we report the nondetection of flares in our data above a 5σ threshold of 95 μJy. Together with the optical nondetection of the most recent stellar maximum expected in 2019, our observations postulate a likely evolution of the internal dynamo of epsilon Eridani.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/105947, title ="The First Extensive Spectroscopic Study of Young Stars in the North America and Pelican Nebulae", author = "Fang, Min and Hillenbrand, Lynne A.", journal = "Astrophysical Journal", volume = "904", number = "2", pages = "Art. No. 146", month = "December", year = "2020", doi = "10.3847/1538-4357/abba84", issn = "1538-4357", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201009-093746303", note = "© 2020 The American Astronomical Society. \n\nReceived 2020 July 16; revised 2020 September 9; accepted 2020 September 10; published 2020 November 27. \n\nMany thanks to the anonymous referee for comments that helped to improve this paper. We thank Michael A. Kuhn for discussions about the NAP region. We recognize the contributions of former Caltech SURF students Daniel DeFelippis and Danika Wellington to our efforts. This paper uses data products produced by the OIR Telescope Data Center, supported by the Smithsonian Astrophysical Observatory. This work has made use of data from the European Space Agency mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC; https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. We use ZTF data, enabled by support from the National Science Foundation under grant AST-1440341, Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Centre at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. \n\nFacilities: Palomar:P200 (Norris) - , Keck:I (DEIMOS) - , MMT (Hectospec) - , Palomar:P48 (ZTF). -", revision_no = "22", abstract = "We present a spectroscopic survey of over 3400 potential members in the North America and Pelican Nebulae (NAP) using several low-resolution (R ≈ 1300–2000) spectrographs: Palomar/Norris, WIYN/Hydra, Keck/DEep Imaging Multi-Object Spectrograph (DEIMOS), and the Multiple Mirror Telescope (MMT)/Hectospec. We identify 580 young stars as likely members of the NAP region based on criteria involving infrared excess, Li I 6708 Å absorption, X-ray emission, parallax, and proper motions. The spectral types of individual spectra are derived by fitting them with templates that are either empirical spectra of pre-main-sequence stars or model atmospheres. The templates are artificially veiled, and a best-fit combination of spectral type and veiling parameter is derived for each star. We use the spectral types with archival photometry to derive V-band extinction and stellar luminosity. From the Hertzsprung–Russell diagram, the median age of the young stars is about 1 Myr, with a luminosity dispersion of ~0.3–0.4 dex. We investigate the photometric variability of the spectroscopic member sample using Zwicky Transient Facility data and conclude that photometric variability, while present, does not significantly contribute to the luminosity dispersion. While larger than the formal errors, the luminosity dispersion is smaller than if veiling were not taken into account in our spectral typing process. The measured ages of the stellar kinematic groups, combined with the inferred ages for embedded stellar populations revealed by Spitzer, suggest a sequential history of star formation in the NAP region.", }