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Characterizing the Cool KOIs. IV. Kepler-32 as a Prototype for the Formation of Compact Planetary Systems throughout the Galaxy

Swift, Jonathan J. and Johnson, John Asher and Morton, Timothy D. and Crepp, Justin R. and Montet, Benjamin T. and Fabrycky, Daniel C. and Muirhead, Philip S. (2013) Characterizing the Cool KOIs. IV. Kepler-32 as a Prototype for the Formation of Compact Planetary Systems throughout the Galaxy. Astrophysical Journal, 764 (1). Art. No. 105. ISSN 0004-637X. doi:10.1088/0004-637X/764/1/105.

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The Kepler space telescope has opened new vistas in exoplanet discovery space by revealing populations of Earth-sized planets that provide a new context for understanding planet formation. Approximately 70% of all stars in the Galaxy belong to the diminutive M dwarf class, several thousand of which lie within Kepler's field of view, and a large number of these targets show planet transit signals. The Kepler M dwarf sample has a characteristic mass of 0.5 M_☉ representing a stellar population twice as common as Sun-like stars. Kepler-32 is a typical star in this sample that presents us with a rare opportunity: five planets transit this star, giving us an expansive view of its architecture. All five planets of this compact system orbit their host star within a distance one-third the size of Mercury's orbit, with the innermost planet positioned a mere 4.3 stellar radii from the stellar photosphere. New observations limit possible false positive scenarios, allowing us to validate the entire Kepler-32 system making it the richest known system of transiting planets around an M dwarf. Based on considerations of the stellar dust sublimation radius, a minimum mass protoplanetary nebula, and the near period commensurability of three adjacent planets, we propose that the Kepler-32 planets formed at larger orbital radii and migrated inward to their present locations. The volatile content inferred for the Kepler-32 planets and order of magnitude estimates for the disk migration rates suggest that these planets may have formed beyond the snow line and migrated in the presence of a gaseous disk. If true, then this would place an upper limit on their formation time of ~10 Myr. The Kepler-32 planets are representative of the full ensemble of planet candidates orbiting the Kepler M dwarfs for which we calculate an occurrence rate of 1.0 ± 0.1 planet per star. The formation of the Kepler-32 planets therefore offers a plausible blueprint for the formation of one of the largest known populations of planets in our Galaxy.

Item Type:Article
Related URLs:
URLURL TypeDescription
Swift, Jonathan J.0000-0002-9486-818X
Johnson, John Asher0000-0001-9808-7172
Morton, Timothy D.0000-0002-8537-5711
Crepp, Justin R.0000-0003-0800-0593
Montet, Benjamin T.0000-0001-7516-8308
Fabrycky, Daniel C.0000-0003-3750-0183
Muirhead, Philip S.0000-0002-0638-8822
Additional Information:© 2013 The American Astronomical Society. Received 2012 October 15; accepted 2012 December 11; published 2013 January 29. This work has benefited from the feedback and suggestions of many people, including but not limited to Andrew Youdin, Leslie Rogers, Peter Goldreich, Hilke Schlichting, and Nairn Baliber. We also thank the anonymous referee for a thorough review.D.C.F. acknowledges support for thisworkwas provided by NASA through Hubble Fellowship grant HF-51272.01-A, awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under 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 theNational Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. This paper includes data collected by the Kepler mission. Funding for the Kepler mission is provided by the NASA Science Mission directorate. The Robo-AO system is supported by collaborating partner institutions, the California Institute of Technology and the Inter-University Centre for Astronomy and Astrophysics, by the National Science Foundation under grant Nos. AST-0906060 and AST-0960343, by a grant from the Mt. Cuba Astronomical Foundation and by a gift from Samuel Oschin.
Funding AgencyGrant Number
NASA Hubble FellowshipHF-51272.01-A
NASANAS 5-26555
Subject Keywords:methods: statistical; planetary systems; planets and satellites: detection; planets and satellites: formation; stars: individual (KID 9787239/KOI-952/Kepler-32)
Issue or Number:1
Record Number:CaltechAUTHORS:20130308-134732086
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Official Citation:Characterizing the Cool KOIs. IV. Kepler-32 as a Prototype for the Formation of Compact Planetary Systems throughout the Galaxy Jonathan J. Swift et al. 2013 ApJ 764 105
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37423
Deposited On:08 Mar 2013 23:34
Last Modified:09 Nov 2021 23:28

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