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

A. Santerne (1) , G. Hébrard (2) , M. Deleuil (3) , M. Havel , A. C. M. Correia (4) , J. -M Almenara , R. Alonso (5) , L. Arnold , S. C. C. Barros (3) , R. Behrend (6, 7) , L. Bernasconi (8) , I. Boisse (3) , A. S. Bonomo , F. Bouchy (9, 2) , G. Bruno , C. Damiani (10) , R. F. Diaz , D. Gravallon , T. Guillot (11) , O. Labrevoir , G. Montagnier (12) , C. Moutou (3) , C. Rinner (13) , N. C. Santos (1, 14) , L. Abe (11) , M. Audejean (15) , P. Bendjoya (11) , C. Gillier , J. Gregorio , P. Martinez (16) , J. Michelet (17) , R. Montaigut , R. Poncy (18) , J. -P. Rivet (11) , G. Rousseau , R. Roy (19) , O. Suarez (20) , M. Vanhuysse , D. Verilhac

1 CAUP - Centro de Astrofísica da Universidade do Porto
2 IAP - Institut d'Astrophysique de Paris
3 LAM - Laboratoire d'Astrophysique de Marseille
4 IMCCE - Institut de Mécanique Céleste et de Calcul des Ephémérides
5 CBMSO - Centro de Biología Molecular Severo Ochoa [Madrid]
6 Geneva Observatory
7 CdR & CdL group
8 Observatoire des Engarouines
9 OHP - Observatoire de Haute-Provence
10 LMNO - Laboratoire de Mathématiques Nicolas Oresme
11 LAGRANGE - Joseph Louis LAGRANGE
12 ESO - European Southern Observatory
13 AUDE - Association des Utilisateurs de Détecteurs Electroniques
14 DFA/FCUP - Departamento de Física e Astronomia [Porto]
15 Observatoire de Chinon
16 EPOC - Environnements et Paléoenvironnements OCéaniques
17 CALA - Club d'Astronomie Lyon Ampéré [Vaulx-en-Velin]
18 Chercheur indépendant
19 EDF R&D STEP - Simulation et Traitement de l'information pour l'Exploitation des systèmes de Production
20 OCA - Observatoire de la Côte d'Azur

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 M-circle dot and 0.70 +/- 0.07 M-circle dot 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, and 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 M-4, and a radius of 0.94(4) +/- 0.12 R-4 and thus a bulk density of 2.1 +/- 1.2 g cm(-3). The planet has an equilibrium temperature of 511 +/- 50K, making it one of the few known members 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 aim of constraining the orbital obliquity of the planet. However, the Rossiter-McLaughlin effect was not clearly detected, resulting in poor constraints on the orbital obliquity of the planet.

Domaines: Astrophysique [astro-ph]

A. Santerne, G. Hébrard, M. Deleuil, M. Havel, A. C. M. Correia, et al.. SOPHIE velocimetry of Kepler transit candidates XII. KOI-1257 b: a highly eccentric three-month period transiting exoplanet. Astronomy and Astrophysics - A&A, 2014, 571, ⟨10.1051/0004-6361/201424158⟩. ⟨hal-01441978⟩