Wednesday, June 25, 2014

KOI-1257b: A Warm Jupiter in an Highly Eccentric Orbit

SOPHIE velocimetry of Kepler transit candidates XII. KOI-1257 b: a highly-eccentric 3-month period transiting exoplanet

Authors:

Santerne et al

Abstract:

In this paper we report a new transiting warm giant planet: KOI-1257 b. It was first detected in photometry as a planet-candidate by the Kepler space telescope and then validated thanks to a radial velocity follow-up with the SOPHIE spectrograph. It orbits its host star with a period of 86.647661 d ± 3 s and a high eccentricity of 0.772 ± 0.045. The planet transits the main star of a metal-rich, relatively old binary system with stars of mass of 0.99 ± 0.05 Msun and 0.70 ± 0.07 Msun for the primary and secondary (respectively). This binary system is constrained thanks to a self-consistent modelling of the Kepler transit light curve, the SOPHIE radial velocities, line bisector and full-width half maximum (FWHM) variations as well as the spectral energy distribution. However, future observations are needed to confirm it. The PASTIS fully-Bayesian software was used to validate the nature of the planet and to determine which star of the binary system is the transit host. By accounting for the dilution from the binary both in photometry and in radial velocity, we find that the planet has a mass of 1.45 ± 0.35 Mjup, and a radius of 0.94 ± 0.12 Rjup, and thus a bulk density of 2.1 ± 1.2 g.cm−3. The planet has an equilibrium temperature of 511 ± 50 K, making it one of the few known membre of the warm-jupiter population. The HARPS-N spectrograph was also used to observe a transit of KOI-1257 b, simultaneously with a joint amateur and professional photometric follow-up, with the aims at constraining the orbital obliquity of the planet. However, the Rossiter-McLaughlin was not clearly detected, resulting in poor constraints on the orbital obliquity of the planet.

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