KEPLER-20: A SUN-LIKE STAR WITH THREE SUB-NEPTUNE EXOPLANETS AND TWO EARTH-SIZE CANDIDATES
- Jet Propulsion Laboratory/California Institute of Technology, Pasadena, CA 91109 (United States)
- Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)
- NASA Ames Research Center, Moffett Field, CA 94035 (United States)
- Department of Astronomy, University of California, Berkeley, CA 94720 (United States)
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)
- Niels Bohr Institute, University of Copenhagen, DK-2100, Copenhagen (Denmark)
- NASA Exoplanet Science Institute/California Institute of Technology, Pasadena, CA 91125 (United States)
- Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)
- Astronomy Department, University of Florida, Gainesville, FL 32111 (United States)
- Department of Astronomy, 525 Davey Lab, The Pennsylvania State University, University Park, PA 16802 (United States)
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)
- McDonald Observatory, University of Texas at Austin, Austin, TX 78712 (United States)
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 2MASS J19104752+4220194. From high-resolution spectroscopy of the star, we find a stellar effective temperature T{sub eff} = 5455 {+-} 100 K, a metallicity of [Fe/H] = 0.01 {+-} 0.04, and a surface gravity of log g = 4.4 {+-} 0.1. We combine these estimates with an estimate of the stellar density derived from the transit light curves to deduce a stellar mass of M{sub *} = 0.912 {+-} 0.034 M{sub Sun} and a stellar radius of R{sub *} = 0.944{sup +0.060}{sub -0.095} R{sub Sun }. For three of the transit signals, we demonstrate that our results strongly disfavor the possibility that these result from astrophysical false positives. We accomplish this by first identifying the subset of stellar blends that reproduce the precise shape of the light curve and then using the constraints on the presence of additional stars from high angular resolution imaging, photometric colors, and the absence of a secondary component in our spectroscopic observations. We conclude that the planetary scenario is more likely than that of an astrophysical false positive by a factor of 2 Multiplication-Sign 10{sup 5} (Kepler-20b), 1 Multiplication-Sign 10{sup 5} (Kepler-20c), and 1.1 Multiplication-Sign 10{sup 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 4.5 {mu}m, 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 3.70 days and 1.91{sup +0.12}{sub -0.21} R{sub Circled-Plus} for Kepler-20b, 10.85 days and 3.07{sup +0.20}{sub -0.31} R{sub Circled-Plus} for Kepler-20c, and 77.61 days and 2.75{sup +0.17}{sub -0.30} R{sub Circled-Plus} 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{sub Circled-Plus} and 16.1 {+-} 3.5 M{sub Circled-Plus }, respectively, and we place an upper limit on the mass of Kepler-20d of 20.1 M{sub Circled-Plus} (2{sigma}).
- OSTI ID:
- 22020460
- Journal Information:
- Astrophysical Journal, Vol. 749, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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