Rappaport, S. and Levine, A. and Chiang, E. and Mellah, I. El. and Jenkins, J. and Kalomeni, B. and Kite, E. S. and Kotson, M. and Nelson, L. and Rousseau-Nepton, L. and Tran, K. (2012) Possible Disintegrating Short-period Super-Mercury Orbiting KIC 12557548. Astrophysical Journal, 752 (1). Art. No. 1. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20120713-152814100
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We report on the discovery of stellar occultations, observed with Kepler, which recur periodically at 15.685 hr intervals, but which vary in depth from a maximum of 1.3% to a minimum that can be less than 0.2%. The star that is apparently being occulted is KIC 12557548, a V = 16 mag K dwarf with T_eff, s ≃ 4400 K. The out-of-occultation behavior shows no evidence for ellipsoidal light variations, indicating that the mass of the orbiting object is less than ~3 M_J (for an orbital period of 15.7 hr). Because the eclipse depths are highly variable, they cannot be due solely to transits of a single planet with a fixed size. We discuss but dismiss a scenario involving a binary giant planet whose mutual orbit plane precesses, bringing one of the planets into and out of a grazing transit. This scenario seems ruled out by the dynamical instability that would result from such a configuration. We also briefly consider an eclipsing binary, possibly containing an accretion disk, that either orbits KIC 12557548 in a hierarchical triple configuration or is nearby on the sky, but we find such a scenario inadequate to reproduce the observations. The much more likely explanation—but one which still requires more quantitative development—involves macroscopic particles escaping the atmosphere of a slowly disintegrating planet not much larger than Mercury in size. The particles could take the form of micron-sized pyroxene or aluminum oxide dust grains. The planetary surface is hot enough to sublimate and create a high-Z atmosphere; this atmosphere may be loaded with dust via cloud condensation or explosive volcanism. Atmospheric gas escapes the planet via a Parker-type thermal wind, dragging dust grains with it. We infer a mass-loss rate from the observations of order 1 M_⊕ Gyr^(–1), with a dust-to-gas ratio possibly of order unity. For our fiducial 0.1 M_⊕ planet (twice the mass of Mercury), the evaporation timescale may be ~0.2 Gyr. Smaller mass planets are disfavored because they evaporate still more quickly, as are larger mass planets because they have surface gravities too strong to sustain outflows with the requisite mass-loss rates. The occultation profile evinces an ingress-egress asymmetry that could reflect a comet-like dust tail trailing the planet; we present simulations of such a tail.
|Additional Information:||© 2012 American Astronomical Society. Received 2012 January 10; accepted 2012 March 18; published 2012 May 18. We thank the anonymous referee for an encouraging and incisive report that motivated us to consider volcanic activity and to examine more quantitatively the ability of the atmosphere to entrain solids; Raymond Jeanloz and Michael Manga for instructive exchanges about vaporizing silicates and volcano ejecta speeds; Josh Carter for discussions about data validations and the viability of a dynamically stable binary planet; Ruth Murray-Clay for input about thermal winds; Robert Szabo for information about properties of RR Lyrae stars; and Bryce Croll, Dan Fabrycky, Ron Gilliland, Meredith Hughes, John Johnson, Heather Knutson, Tim Morton, Margaret Pan, Erik Petigura, and Josh Winn for stimulating discussions about follow-up observations. We consulted with Ron Remillard, Rob Simcoe, and Adam Burgasser about spectral classifications. We also thank Robert Lamontagne and the staff at the Observatoire Astronomique du Mont-Mégantic for their assistance. E.C. is grateful for support from the National Science Foundation, and for useful and encouraging feedback from participants of the Berkeley Planet and Star Formation Seminar, including Ryan= O’Leary and Geoff Marcy who shared their own analyses of the Kepler data on KIC 12557548. L.N. thanks the Natural Sciences and Engineering Research Council (NSERC) of Canada for financial support. B.K. is grateful to the MIT Kavli Institute for Astrophysics and Space Research for the hospitality they extended during her visit and the support provided by the Turkish Council of Higher Education.|
|Subject Keywords:||eclipses; occultations; planetary systems; planets and satellites: general|
|Official Citation:||Possible Disintegrating Short-period Super-Mercury Orbiting KIC 12557548 S. Rappaport et al. 2012 ApJ 752 1|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||13 Jul 2012 23:04|
|Last Modified:||26 Dec 2012 15:32|
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