Gautier, Thomas N., III and Ciardi, David R. (2012) Kepler-20: A Sun-like Star with Three Sub-Neptune Exoplanets and Two Earth-size Candidates. Astrophysical Journal, 749 (1). Art. No. 15. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20120103-074846437
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We present the discovery of the Kepler-20 planetary system, which we initially identified through the detection of five distinct periodic transit signals in the Kepler light curve of the host star 2MASSJ19104752+4220194. We find a stellar effective temperature T_(eff)=5455±100K, a metallicity of [Fe/H]=0.01±0.04, and a surface gravity of log(g)=4.4±0.1. Combined with an estimate of the stellar density from the transit light curves we deduce a stellar mass of M_*=0.912±0.034 M_⊙ and a stellar radius of R_*=0.944^(+0.060)_(-0.095) R_⊙. For three of the transit signals, our results strongly disfavor the possibility that these result from astrophysical false positives. We conclude that the planetary scenario is more likely than that of an astrophysical false positive by a factor of 2 x 10^5 (Kepler-20b), 1 x 10^5 (Kepler-20c), and 1.1 x 10^3 (Kepler-20d), sufficient to validate these objects as planetary companions. For Kepler-20c and Kepler-20d, the blend scenario is independently disfavored by the achromaticity of the transit: From Spitzer data gathered at 4.5µm, we infer a ratio of the planetary to stellar radii of 0.075±0.015 (Kepler-20c) and 0.065±0.011 (Kepler-20d), consistent with each of the depths measured in the Kepler optical bandpass. We determine the orbital periods and physical radii of the three confirmed planets to be 3.70d and 1.91^(+0.12)_(-0.21) R_⊕ for Kepler-20b, 10.85 d and 3.07^(+0.20)_(-0.31) R_⊕ for Kepelr-20c, and 77.61 d and 2.75^(+0.17)_(-0.30) R_⊕ for Kepler-20d. From multi-epoch radial velocities, we determine the masses of Kepler-20b and Kepler-20c to be 8.7±2.2 M_⊕ and 16.1±3.5 M_⊕, respectively, and we place an upper limit on the mass of Kepler-20d of 20.1 M_⊕ (2 σ).
|Additional Information:||© 2012 The American Astronomical Society. Received 2011 November 28, accepted for publication 2011 December 19; Published 2012 March 16. Kepler was competitively selected as the tenth Discovery mission. Funding for this mission is provided by NASA’s Science Mission Directorate. The authors thank many people who gave so generously of their time to make this mission a success. This work is also based in part on observations made with the Spitzer Space Telescope, which is 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. We would like to thank the Spitzer staff at IPAC and in particular Nancy Silbermann for scheduling the Spitzer observations of this program. 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.|
|Subject Keywords:||eclipses; planetary systems; stars: individual (Kepler-20, KIC 6850504, 2MASS J19104752+4220194)|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||13 Apr 2012 18:42|
|Last Modified:||26 Dec 2012 14:39|
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