A window on exoplanet dynamical histories : Rossiter-McLaughlin observations of WASP-13b and WASP-32b
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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 λ = 8º+13-12 and λ = -2º+17-19, respectively. Both WASP-13 and WASP-32 have Teff <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 Prot = 11.6 ± 1.0 days. This rotation period is in agreement with the predicted stellar rotation period calculated from the stellar radius, R*, and vsin i if a stellar inclination of i* = 90º is assumed. With the determined rotation period, the true 3D angle between the stellar rotation axis and the planetary orbit, ψ, was found to be ψ = 11º ± 14º. We conclude with a discussion on the alignment of systems around cool host stars with Teff <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.
Brothwell , R D , Watson , C A , Hebrard , G , Triaud , A H M J , Cegla , H M , Santerne , A , Hebrard , E , Anderson , D R , Pollacco , D , Simpson , E K , Bouchy , F , Brown , D J A , Chew , Y G M , Cameron , A C , Armstrong , D J , Barros , S C C , Bento , J , Bochinski , J , Burwitz , V , Busuttil , R , Delrez , L , Doyle , A P , Faedi , F , Fumel , A , Gillon , M , Haswell , C A , Hellier , C , Jehin , E , Kolb , U , Lendl , M , Liebig , C E , Maxted , P F L , McCormac , J , Miller , G , Norton , A J , Pepe , F , Queloz , D , Rodriguez , J , Segransan , D , Skillen , I , Smalley , B , Stassun , K G , Udry , S , West , R G & Wheatley , P J 2014 , ' A window on exoplanet dynamical histories : Rossiter-McLaughlin observations of WASP-13b and WASP-32b ' , Monthly Notices of the Royal Astronomical Society , vol. 440 , no. 4 , pp. 3392-3401 . https://doi.org/10.1093/mnras/stu520
Monthly Notices of the Royal Astronomical Society
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
DescriptionRDB acknowledges support from the Queen's University Belfast Department for Education and Learning (DEL) university scholarship. CAW acknowledges support by STFC grant ST/I001123/1. A. H. M. J. Triaud is Swiss National Science Foundation fellow under grant number PBGEP2-145594. AS acknowledges the support from the European Research Council/European Community under the FP7 through Starting Grant agreement number 239953.
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