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Centro de Astrofísica da Universidade do Porto

SOPHIE velocimetry of Kepler transit candidates
V. The three hot Jupiters KOI-135b, KOI-204b and KOI-203b (alias Kepler-17b)

A. S. Bonomo, G. Hébrard, A. Santerne, N. C. Santos, M. Deleuil, J.-M. Almenara, F. Bouchy, R. F. Díaz, C. Moutou, M. Vanhuysse

Abstract
We report the discovery of two new transiting hot Jupiters, KOI-135b and KOI-204b, that were previously identified as planetary candidates by Borucki et al. 2011, and, independently of the Kepler team, confirm the planetary nature of Kepler-17b, recently announced by D´esert et al. 2011. Radial-velocity measurements, taken with the SOPHIE spectrograph at the Observatoire de Haute- Provence (France), and Kepler photometry (Q1 and Q2 data) were used to derive the orbital, stellar and planetary parameters. KOI-135b and KOI-204b orbit their parent stars in ~ 3.02 and 3.25 days, respectively. They have approximately the same radius, Rp = 1.20 ± 0.06 RJup and 1.24 ± 0.07 RJup, but different masses Mp = 3.23 ± 0.19 MJup and 1.02 ± 0.07 MJup. As a consequence, their bulk densities differ by a factor of four, ρp = 2.33 ± 0.36 g cm-3 (KOI-135b) and 0.65 ± 0.12 g cm-3 (KOI-204b), meaning that their interior structures are different. All the three planets orbit metal-rich stars with [Fe/H] ~ 0.3 dex. Our SOPHIE spectra of Kepler-17b, used both to measure the radial-velocity variations and determine the atmospheric parameters of the host star, allow us to refine the characterisation of the planetary system. In particular we found the radial-velocity semi-aMplitude and the stellar mass to be respectively slightly smaller and larger than D´esert et al. These two quantities, however, coMpensate and lead to a planetary mass fully consistent with D´esert et al. : our analysis gives Mp = 2.47 ± 0.10 MJup and Rp = 1.33 ± 0.04 RJup. We found evidence for a younger age of this planetary system, t < 1.8 Gyr, which is supported by both evolutionary tracks and gyrochronology. Finally, we confirm the detection of the optical secondary eclipse by D´esert et al. and found also the brightness phase variation with the Q1 and Q2 Kepler data. The latter indicates a low redistribution of stellar heat to the night side (< 16% at 1-σ), if the optical planetary occultation comes entirely from thermal flux. The geometric albedo is Ag < 0.12 (1-σ).

Keywords
planetary systems – stars: fundamental parameters – techniques: photometric – techniques: spectroscopic – techniques: radial velocities

Astronomy and Astrophysics
Volume 538, Page A96_1
February 2012

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