2011A&A...533A.113M

We report the measurement of the spin-orbit angle of the extra-solar planets HAT-P-8b, HAT-P-9b, HAT-P-16b, and HAT-P-23b, based on spectroscopic observations performed at the Observatoire de Haute-Provence with the SOPHIE spectrograph on the 1.93-m telescope. Radial velocity measurements of the Rossiter-McLaughlin effect show the detection of an apparent prograde, aligned orbit for all systems. The projected spin-orbit angles are found to be λ=-17°^+9.2_–11.5, -16°±8°, -10°±16°, and+15° ±22 ° for, HAT-P-8, HAT-P-9, HAT-P-16, and HAT-P-23, respectively, with corresponding projected rotational velocities of 14.5±0.8, 12.5±1.8, 3.9±0.8, and 7.8±1.6km/s. These new results increase to 37 the number of accurately measured spin-orbit angles in transiting extrasolar systems. We conclude by drawing a tentative picture of the global behaviour of orbital alignement, involving the complexity and diversity of possible mechanisms.