SOPHIE velocimetry of Kepler transit candidates VIII. KOI-205 b: a brown-dwarf companion to a K-type dwarf

We report the discovery of the discovery of a transiting brown dwarf companion to KOI-205, a K0 main-sequence star, in a 11.720125-day period transits were detected by the Kepler space telescope, and the reflex motion of the star was measured using radial velocity observations obtained with the SOPHIE spectrograph. The atmospheric parameters of the host stars were determined from the high-resolution, high signal-to-noise ratio ESPaDOns spectra obtained for this purpose. Together with spectrophotometric recovered from the literature, these spectra indicate that the star is a mildly metallic K0 dwarf with T-eff 5237 +/- 60 K. of the companion is 39.9 +/- 1.0 M-Jup and its radius is 0.81 +/- 0.02 R-Jup, in agreement with current theoretical predictions. This is the first time a nona fide brown dwarf companion is detected in orbit around a star of this type. The formation and orbital evolution of brown dwarf companions is briefly discussed in the light of this new discovery.