SOPHIE velocimetry of Kepler transit candidates

XVI. Tomographic measurement of the low obliquity of KOI-12b, a warm Jupiter transiting a fast rotator^⋆

¹ Institut d’astrophysique de Paris, UMR 7095 CNRS, Université Pierre & Marie Curie, 98bis boulevard Arago, 75014 Paris, France
² Observatoire de l’Université de Genève, 51 chemin des Maillettes, 1290 Sauverny, Switzerland
e-mail: vincent.bourrier@unige.ch
³ Observatoire de Haute-Provence, CNRS/OAMP, 04870 Saint-Michel-l’ Observatoire, France
⁴ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
⁵ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
⁶ UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), UMR 5274, 38041 Grenoble, France
⁷ INAF–Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
⁸ Canada-France-Hawaii Telescope Corporation, 65-1238 Mamalahoa Hwy, Kamuela, HI 96743, USA

Received: 26 January 2015
Accepted: 20 April 2015

Abstract

We present the detection and characterization of the transiting warm Jupiter KOI-12b, first identified with Kepler with an orbital period of 17.86 days. We combine the analysis of Kepler photometry with Doppler spectroscopy and line-profile tomography of time-series spectra obtained with the SOPHIE spectrograph to establish its planetary nature and derive its properties. To derive reliable estimates for the uncertainties on the tomographic model parameters, we devised an empirical method of calculating statistically independent error bars on the time-series spectra. KOI-12b has a radius of 1.43 ± 0.13 R_Jup and a 3σ upper mass limit of 10 M_Jup. It orbits a fast-rotating star (vsini_⋆ = 60.0 ± 0.9 km s^-1) with mass and radius of 1.45 ± 0.09 M_⊙ and 1.63 ± 0.15 R_⊙, located at 426 ± 40 pc from the Earth. Doppler tomography allowed higher precision on the obliquity to be reached by comparison with analysis of the Rossiter-McLaughlin radial velocity anomaly, and we find that KOI-12b lies on a prograde, slightly misaligned orbit with low sky-projected obliquity λ = 12.6${\stackrel{\mathrm{+}\mathrm{3.0}}{{-2.9}_{}}}^{\mathrm{◦}}$. The properties of this planetary system, with a 11.4 mag host star, make of KOI-12b a precious target for future atmospheric characterization.