Kepler-432 b: a massive warm Jupiter in a 52-day eccentric orbit transiting a giant star^{⋆,⋆⋆,⋆⋆⋆}

¹ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
e-mail: mortiz@lsw.uni-heidelberg.de
² Instituto de Astrofísica de Canarias, C. Vía Láctea S/N, 38205 La Laguna, Tenerife, Spain
³ Departamento de Astrofísica, Universidad de La Laguna, 38200, La Laguna, Tenerife, Spain
⁴ Isaac Newton Group of Telescopes, Apartado de Correos 321, 38700 Santa Cruz de Palma, Spain
⁵ Nordic Optical Telescope, Apartado 474, 38700 Santa Cruz de La Palma, Spain

Received: 11 October 2014
Accepted: 28 November 2014

Abstract

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 2.2 m 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_p = 5.84 ± 0.05M_Jup and a high eccentricity of e = 0.478 ± 0.004. With a semi-major axis of a = 0.303 ± 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 γ̇ = 0.44 ± 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.