The retrograde orbit of the HAT-P-6b exoplanet

G. HÉBRARD; D. EHRENREICH; F. BOUCHY; X. DELFOSSE; C. MOUTOU; L. ARNOLD; I. BOISSE; X. BONFILS; R. F. DÍAZ; A. EGGENBERGER; T. FORVEILLE; A. M. LAGRANGE; C. LOVIS; F. PEPE; C. PERRIER; D. QUELOZ; A. SANTERNE; N. C. SANTOS; D. SÉGRANSAN; S. UDRY; A. VIDAL-MADJAR

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2011 vol. 527 p. 1 - 4

0004-6361

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.