Discovery and characterization of WASP-6b, an inflated sub-Jupiter mass planet transiting a solar-type star ^*,**

¹ Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, Bât. B5C, Liège 1, Belgium e-mail: michael.gillon@obs.unige.ch
² Observatoire de Genève, Université de Genève, 51 Chemin des Maillettes, 1290 Sauverny, Switzerland
³ Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK
⁴ Astrophysics Research Centre, School of Mathematics & Physics, Queen's University, University Road, Belfast, BT7 1NN, UK
⁵ Department of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UK
⁶ School of Physics and Astronomy, University of St. Andrews, North Haugh, Fife, KY16 9SS, UK
⁷ Department of Astronomy, Harvard University, 60 Garden Street, MS 10, Cambridge, Massachusetts 02138, USA
⁸ Las Cumbres Observatory, 6740 Cortona Dr. Suite 102, Santa Barbara, CA 93117, USA
⁹ Department of Physics, University of Warwick, Coventry, CV4 7AL, UK

Received: 29 January 2009
Accepted: 4 May 2009

Abstract

We report the discovery of WASP-6b, an inflated sub-Jupiter mass planet transiting every  days a mildly metal-poor solar-type star of magnitude . A combined analysis of the WASP photometry, high-precision followup transit photometry and radial velocities yield a planetary mass M_J and radius R_J, resulting in a density . The mass and radius for the host star are and . The non-zero orbital eccentricity that we measure suggests that the planet underwent a massive tidal heating ~1 Gyr ago that could have contributed to its inflated radius. High-precision radial velocities obtained during a transit allow us to measure a sky-projected angle between the stellar spin and orbital axis  deg. In addition to similar published measurements, this result favors a dominant migration mechanism based on tidal interactions with a protoplanetary disk.