SOPHIE velocimetry of Kepler transit candidates. II. KOI-428b: a hot Jupiter transiting a subgiant F-star

We report the discovery of a hot Jupiter transiting a subgiant star with an orbital period of 6.87 days. This discovery was aided by public photometric data from the Kepler space mission and new radial velocity observations obtained by the SOPHIE spectrograph. The planet KOI-428b, with a radius of 1.17 ± 0.04 R_Jup and a mass of 2.2 ± 0.4 M_Jup, orbits an F5IV star with R _⋆ = 2.13 ± 0.06 R_⊙, M _⋆ = 1.48 ± 0.06 M_⊙, and T_eff = 6510 ± 100 K. The star KOI-428 is the largest and the most evolved star discovered so far with a transiting planet.

Based on observations made with the 1.93-m telescope at Observatoire de Haute-Provence (CNRS), France.