SOPHIE velocimetry of Kepler transit candidates XIV. A joint photometric, spectroscopic, and dynamical analysis of the Kepler-117 system

TL;DR

This study combines photometric, spectroscopic, and dynamical data to precisely characterize the Kepler-117 planetary system, revealing distinct planetary masses and low eccentricities through integrated analysis of transit timing variations and radial velocities.

Contribution

It introduces a joint MCMC approach that incorporates TTVs and radial velocities for comprehensive system parameter estimation.

Findings

Kepler-117 b has a mass of 0.094 ± 0.033 M_J

Kepler-117 c has a mass of 1.84 ± 0.18 M_J

Including TTVs reduces uncertainties in system parameters

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 $\simeq 18.8$ and $\simeq 50.8$ 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 ($0.094 \pm 0.033$ and $1.84 \pm 0.18$ M$_{\rm J}$) and low orbital eccentricities ($0.0493 \pm 0.0062$ and $0.0323 \pm 0.0033$). 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.