The Kepler-20 planetary system

From high-resolution spectroscopy of the star, we find a stellar effective temperature T_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_*_ = 0.912+/-0.034 M_{sun}_and a stellar radius of R_*_ = 0.944^+0.060^_-0.095_R_{sun}_.

For three of the transit signals, we demonstrate that our results strongly disfavor the possibility that these result from astrophysical false positives. We determine the orbital periods and physical radii of the three confirmed planets to be 3.70 days and 1.91^+0.12^_-0.21_R_{earth}_ for Kepler-20b, 10.85 days and 3.07^+0.20^_-0.31_R_{earth}_ for Kepler-20c, and 77.61 days and 2.75^+0.17^_-0.30_R_{earth}_ for Kepler-20d.