The Photoeccentric Effect and Proto-hot Jupiters. III. A Paucity of Proto-hot Jupiters on Super-eccentric Orbits

Creators: Dawson, Rebekah I.; Murray-Clay, Ruth A.; Johnson, John Asher

Abstract

Gas giant planets orbiting within 0.1 AU of their host stars are unlikely to have formed in situ and are evidence for planetary migration. It is debated whether the typical hot Jupiter smoothly migrated inward from its formation location through the proto-planetary disk, or was perturbed by another body onto a highly eccentric orbit, which tidal dissipation subsequently shrank and circularized during close stellar passages. Socrates and collaborators predicted that the latter model should produce a population of super-eccentric proto-hot Jupiters readily observable by Kepler. We find a paucity of such planets in the Kepler sample, which is inconsistent with the theoretical prediction with 96.9% confidence. Observational effects are unlikely to explain this discrepancy. We find that the fraction of hot Jupiters with an orbital period P > 3 days produced by the star-planet Kozai mechanism does not exceed (at two-sigma) 44%. Our results may indicate that disk migration is the dominant channel for producing hot Jupiters with P > 3 days. Alternatively, the typical hot Jupiter may have been perturbed to a high eccentricity by interactions with a planetary rather than stellar companion, and began tidal circularization much interior to 1 AU after multiple scatterings. A final alternative is that early in the tidal circularization process at high eccentricities tidal circularization occurs much more rapidly than later in the process at low eccentricities, although this is contrary to current tidal theories.

Additional Information

© 2015 American Astronomical Society. Received 2012 October 26; accepted 2014 October 20; published 2014 December 22. We are thankful to the anonymous referee(s) for an insightful report that improved the paper, and in particular for advocating more conservative assumptions about the completeness of the Kepler pipeline. R.I.D. gratefully acknowledges the National Science Foundation Graduate Research Fellowship under grant DGE-1144152 and the Miller Institute for Basic Research in Science, University of California, Berkeley. J.A.J. is grateful for the generous grant support provided by the Alfred P. Sloan and David & Lucile Packard foundations. We are grateful to Smadar Naoz for many enlightening discussions and comments, including opening our eyes to other possibilities in Section 4, for which we also thank Simon Albrecht and Fred Rasio. Many thanks to Adrian Barker, Rick Greenberg, Renu Malhotra, Francesca Valsecchi, and especially Brad Hansen for tidal insights; to Katherine Deck, Will Farr, Vicky Kalogera, Yoram Lithwick, and Matthew Payne for helpful dynamical discussions; to Will Farr and Moritz Günther for helpful statistical discussions; to Courtney Dressing and Francois Fressin for Kepler assistance; and to Joel Hartmann for helpful discussions about the ground-based sample. We are grateful to Subo Dong for constructive comments on a manuscript draft. Thanks to Joshua Carter, Boas Katz, Doug Lin, Geoff Marcy, Darin Ragozzine, Kevin Schlaufman, and Aristotle Socrates for helpful comments, and to Thomas Barclay, Christophe Burke, Jon Jenkins, and Jason Rowe for helpful discussions of Kepler's completeness for giant planets. We benefitted from helpful conversations with Thomas Barclay about candidate vetting and Howard Isaacson and Rea Kolb about false positives. We are very grateful to Chelsea Huang for helpful discussions and for providing us with a detrended light curve for KIC 6805414. R.I.D. thanks David Charbonneau, Sean Andrews, Debra Fischer,Matt Holman, and Abraham Loeb for helpful comments on the thesis chapter version of this manuscript. Special thanks to J. Zachary Gazak for helpful modifications to the TAP code. We thank Dáithí Stone for making his library of IDL routines available. This paper includes data collected by the Kepler mission. Funding for the Kepler mission is provided by the NASA Science Mission directorate. We are grateful to Kepler team for their work in making this revolutionizing mission possible and making the rich Kepler data set available. Some of the data presented in this paper were obtained from the Multimission Archive at the Space Telescope Science Institute (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 NNX09AF08G and by other grants and contracts. This research has made use of the Exoplanet Orbit Database, and the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program.

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