We study the Kepler object Kepler-432 , an evolved star ascending the red giant branch .
By deriving precise radial velocities from multi-epoch high-resolution spectra of Kepler-432 taken with the CAFE spectrograph at the 2.2m telescope of Calar Alto Observatory and the FIES spectrograph at the Nordic Optical Telescope of Roque de Los Muchachos Observatory , we confirm the planetary nature of the object Kepler-432 b , which has a transit period of 52 days .
We find a planetary mass of M _ { \mathrm { p } } = 5.84 \pm 0.05 \mathrm { M } _ { \mathrm { Jup } } and a high eccentricity of e = 0.478 \pm 0.004 .
With a semi-major axis of a = 0.303 \pm 0.007 AU , Kepler-432 b is the first bona fide warm Jupiter detected to transit a giant star .
We also find a radial velocity linear trend of \dot { \gamma } = 0.44 \pm 0.04 m s ^ { -1 } d ^ { -1 } , which suggests the presence of a third object in the system .
Current models of planetary evolution in the post-main-sequence phase predict that Kepler-432 b will be most likely engulfed by its host star before the latter reaches the tip of the red giant branch .