A window on exoplanet dynamical histories: Rossiter-McLaughlin observations of WASP-13b and WASP-32b

R. D. Brothwell , C. A. Watson , G. Hebrard , A. H. M. J. Triaud , H. M. Cegla , A. Santerne (1) , E. Hebrard , D. R. Anderson , D. Pollacco , E. K. Simpson , F. Bouchy , D. J. A. Brown , Y. Gomez Maqueo Chew , A. Collier Cameron , D. J. Armstrong , S. C. C. Barros , J. Bento , J. Bochinski , V. Burwitz , R. Busuttil , L. Delrez , A. P. Doyle , F. Faedi , A. Fumel , M. Gillon , C. A. Haswell , C. Hellier , E. Jehin , U. Kolb , M. Lendl , C. Liebig , P. F. L. Maxted , J. Mccormac , G. R. M. Miller , A. J. Norton , F. Pepe , D. Queloz , J. Rodriguez , D. Segransan , I. Skillen , B. Smalley , K. G. Stassun , S. Udry , R. G. West , P. J. Wheatley

1 LAM - Laboratoire d'Astrophysique de Marseille

We present Rossiter-McLaughlin observations of WASP-13b and WASP-32b and determine the sky-projected angle between the normal of the planetary orbit and the stellar rotation axis (lambda). WASP-13b and WASP-32b both have prograde orbits and are consistent with alignment with measured sky-projected angles of lambda = 8 degrees(+13)(-12) and lambda = -2 degrees(+17)(-19), respectively. Both WASP-13 and WASP-32 have T-eff \textless 6250 K, and therefore, these systems support the general trend that aligned planetary systems are preferentially found orbiting cool host stars. A Lomb-Scargle periodogram analysis was carried out on archival SuperWASP data for both systems. A statistically significant stellar rotation period detection (above 99.9 per cent confidence) was identified for the WASP-32 system with P-rot = 11.6 +/- 1.0 days. This rotation period is in agreement with the predicted stellar rotation period calculated from the stellar radius, R-*, and nu sin i if a stellar inclination of i(*) = 90 degrees is assumed. With the determined rotation period, the true 3D angle between the stellar rotation axis and the planetary orbit, psi, was found to be psi = 11 degrees +/- 14 degrees. We conclude with a discussion on the alignment of systems around cool host stars with T-eff \textless 6150 K by calculating the tidal dissipation time-scale. We find that systems with short tidal dissipation time-scales are preferentially aligned and systems with long tidal dissipation time-scales have a broad range of obliquities.

Domaines: Astrophysique [astro-ph]

R. D. Brothwell, C. A. Watson, G. Hebrard, A. H. M. J. Triaud, H. M. Cegla, et al.. A window on exoplanet dynamical histories: Rossiter-McLaughlin observations of WASP-13b and WASP-32b. Monthly Notices of the Royal Astronomical Society, 2014, 440 (4), pp.3392--3401. ⟨10.1093/mnras/stu520⟩. ⟨hal-01434396⟩