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^{\rm + 0.0000022 }_ $ 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 $M_{\rm p} = 0.503^_$ $M_{\rm J}$ and radius $R_{\rm p} = 1.224^_$ $R_{\rm J}$, resulting in a density $\rho_{\rm p} = 0.27 \pm 0.05$ $\rho_{\rm J}$. The mass and radius for the host star are $M_\ast = 0.88^_$ $M_\odot$ and $R_\ast = 0.870^_$ $R_\odot$. The non-zero orbital eccentricity $e = 0.054^{\rm +0.018}_$ 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 $\beta = 11^_$ deg. In addition to similar published measurements, this result favors a dominant migration mechanism based on tidal interactions with a protoplanetary disk.