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

We report the discovery of WASP-6b, an inflated sub-Jupiter mass planet transiting every 3.3610060^{+ 0.0000022} _{- 0.0000035} days a mildly metal-poor solar-type star of magnitude V = 11.9. A combined analysis of the WASP photometry, high-precision followup transit photometry and radial velocities yield a planetary mass M_p = 0.503^+0.019_-0.038 M_J and radius R_p = 1.224^+0.051_-0.052 R_J, resulting in a density ρ_p = 0.27 ± 0.05 ρ_J. The mass and radius for the host star are M_ast = 0.88^+0.05_-0.08 M_⊙ and R_ast = 0.870^+0.025_-0.036 R_⊙. The non-zero orbital eccentricity e = 0.054^+0.018_-0.015 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 β = 11⁺¹⁴_-18 deg. In addition to similar published measurements, this result favors a dominant migration mechanism based on tidal interactions with a protoplanetary disk.

Based on data collected with the HARPS spectrograph at ESO La Silla Observatory in the programs 082.C-0040(E) and 082.C-0608. The photometric time-series and radial velocities (Tables 4, 5) used in this work are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/501/785