Spin-orbit inclinations of the exoplanetary systems HAT-P-8b, HAT-P-9b, HAT-P-16b, and HAT-P-23b ^⋆

¹ Laboratoire d’Astrophysique de Marseille, UMR 6110, OAMP, CNRS and Univ. de Provence, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
e-mail: Claire.Moutou@oamp.fr
² Institut d’Astrophysique de Paris, UMR 7095 CNRS, Université Pierre and Marie Curie, 98bis boulevard Arago, 75014 Paris, France
³ Observatoire de Haute-Provence, CNRS and OAMP, 04870 Saint-Michel l’Observatoire, France
⁴ Observatoire de Genève, Université de Genève, 51 Chemin des Maillettes, 1290 Sauverny, Switzerland
⁵ UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble 38041, France
⁶ Centro de Astrofísica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
⁷ Association Adagio, L’Observatoire, 31540 Belesta Lauragais, France
⁸ Université Toulouse III, UMR5187, 118 route de Narbonne 31062 Toulouse, France
⁹ Oversky, 47 Allée des Palanques, 33127 Saint Jean d’Illac, France
¹⁰ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Portugal

Received: 21 February 2011
Accepted: 18 May 2011

Abstract

We report the measurement of the spin-orbit angle of the extra-solar planets HAT-P-8 b, HAT-P-9 b, HAT-P-16 b, and HAT-P-23 b, 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°$\begin{array}{}\mathrm{+}\mathrm{9.2}\\ -11.5\end{array}$, −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 ± 1.6  km s^-1. 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.