2008A&A...481..529L

In this paper, we report a refined determination of the orbital parameters and the detection of the Rossiter-McLaughlin effect of the recently discovered transiting exoplanet HD 147506b (HAT-P-2b). The large orbital eccentricity at the short orbital period of this exoplanet is unexpected and is distinguishing from other known transiting exoplanets. We performed high-precision radial velocity spectroscopic observations of HD 147506 (HAT-P-2) with the new spectrograph SOPHIE, mounted on the 1.93 m telescope at the Haute-Provence observatory (OHP). We obtained 63 new measurements, including 35 on May 14 and 20 on June 11, when the planet was transiting its parent star. The radial velocity (RV) anomaly observed illustrates that HAT-P-2b orbital motion is set in the same direction as its parent star spin. The sky-projected angle between the normal of the orbital plane and the stellar spin axis, λ=0.2^+12.2_–12.5°, is consistent with zero. The planetary and stellar radii were re-determined, yielding R_p=0.951^+0.039_–0.053R_Jup, R_s=1.416^+0.040_–0.062R_☉. The mass (M_p=8.62^+0.39_–0.55M_Jup) and radius of HAT-P-2b indicate a density of 12.5^+2.6_–3.6g/cm3, suggesting an object in between the known close-in planets with typical density of the order of 1g/cm3, and the very low-mass stars, with density greater than 50g/cm3.