Volume 527, March 2011
|Number of page(s)||4|
|Published online||09 February 2011|
Letters to the Editor
Institut d’Astrophysique de Paris, UMR7095 CNRS, Université Pierre
& Marie Curie,
98bis boulevard Arago,
2 Observatoire de Haute-Provence, CNRS/OAMP, 04870 Saint-Michel-l’Observatoire, France
3 UJF-Grenoble 1 / CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), UMR 5274, 38041 Grenoble, France
4 Laboratoire d’Astrophysique de Marseille, Univ. de Provence, CNRS (UMR6110), 38 rue F. Joliot Curie, 13388 Marseille Cedex 13, France
5 Centro de Astrofísica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
6 Observatoire de Genève, Université de Genève, 51 Chemin des Maillettes, 1290 Sauverny, Switzerland
7 Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Portugal
Received: 15 December 2010
Accepted: 26 January 2011
We observed the transit of the HAT-P-6b exoplanet across its host star with the SOPHIE spectrograph (OHP, France). The resulting stellar radial velocities display the Rossiter-McLaughlin anomaly and reveal a retrograde orbit: the planetary orbital spin and the stellar rotational spin point in approximately opposite directions. A fit to the anomaly measures a sky-projected angle λ = 166° ± 10° between these two spin axes. All seven known retrograde planets are hot Jupiters with masses Mp < 3 MJup. About two thirds of the planets in this mass range, however, are prograde and aligned (λ ≃ 0°). In contrast, most of the more massive planets (Mp > 4 MJup) are prograde but misaligned. Different mechanisms may therefore be responsible for planetary obliquities above and below ~3.5 MJup.
Key words: planets and satellites: dynamical evolution and stability / techniques: radial velocities / planetary systems / stars: individual: HAT-P-6
Based on observations collected with the SOPHIE spectrograph on the 1.93-m telescope at Observatoire de Haute-Provence (CNRS), France, by the SOPHIE Consortium (program 10A.PNP.CONS).
SOPHIE radial velocities are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (126.96.36.199) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/527/L11
© ESO, 2011
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