SOPHIE velocimetry of Kepler transit candidates

XIV. A joint photometric, spectroscopic, and dynamical analysis of the Kepler-117 system^⋆,⋆⋆

¹ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille), UMR 7326, 13388 Marseille, France
e-mail: giovanni.bruno@lam.fr
² Centro de Astrofísica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
³ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, PT 4150-762 Porto, Portugal
⁴ Observatoire Astronomique de l’Université de Genève, 51 chemin des Maillettes, 1290 Versoix, Switzerland
⁵ INAF – Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
⁶ Observatoire de Haute-Provence, 04670 Saint Michel l’Observatoire, France
⁷ Institut d’Astrophysique de Paris, UMR 7095 CNRS, Université Pierre & Marie Curie, 98bis boulevard Arago, 75014 Paris, France

Received: 11 July 2014
Accepted: 8 November 2014

Abstract

As part of our follow-up campaign of Kepler planets, we observed Kepler-117 with the SOPHIE spectrograph at the Observatoire de Haute-Provence. This F8-type star hosts two transiting planets in non-resonant orbits. The planets, Kepler-117 b and c, have orbital periods ≃ 18.8 and ≃ 50.8 days, and show transit-timing variations (TTVs) of several minutes. We performed a combined Markov chain Monte Carlo (MCMC) fit on transits, radial velocities, and stellar parameters to constrain the characteristics of the system. We included the fit of the TTVs in the MCMC by modeling them with dynamical simulations. In this way, consistent posterior distributions were drawn for the system parameters. According to our analysis, planets b and c have notably different masses (0.094 ± 0.033 and 1.84 ± 0.18M_J) and low orbital eccentricities (0.0493 ± 0.0062 and 0.0323 ± 0.0033). The uncertainties on the derived parameters are strongly reduced if the fit of the TTVs is included in the combined MCMC. The TTVs allow measuring the mass of planet b although its radial velocity amplitude is poorly constrained. Finally, we checked that the best solution is dynamically stable.