K2-287b: an Eccentric Warm Saturn transiting a G-dwarf

Abstract

We report the discovery of K2-287b, a Saturn mass planet orbiting a G-dwarf with a period of $P\approx 15$ days. First uncovered as a candidate using K2 campaign 15 data, follow-up photometry and spectroscopy were used to determine a mass of $M_P=0.317\pm 0.026$ $M_J$, radius $R_P=0.833\pm 0.013$ $R_J$, period $P=14.893291\pm 0.000025$ days and eccentricity $e=0.476\pm 0.026$. The host star is a metal-rich $V=11.410\pm 0.129$ mag G dwarf for which we estimate a mass $M_{\ast }=1.056$ $M_{\odot }$, radius $R_{\ast }=1.07\pm 0.01$ $R_{\odot }$, metallicity [Fe/H] = $0.20\pm 0.05$ and $T_{eff}=5673\pm 75$ K. This warm eccentric planet with a time-averaged equilibrium temperature of $T_{eq}\approx 800$ K adds to the small sample of giant planets orbiting nearby stars whose structure is not expected to be affected by stellar irradiation. Follow-up studies on the K2-287 system could help in constraining theories of migration of planets in close-in orbits.

Accepted in the Astronomical Journal. 9 figures, 3 tables