Journal Article

Rossiter–McLaughlin effect measurements for WASP-16, WASP-25 and WASP-31*

D. J. A. Brown, A. Collier Cameron, D. R. Anderson, B. Enoch, C. Hellier, P. F. L. Maxted, G. R. M. Miller, D. Pollacco, D. Queloz, E. Simpson, B. Smalley, A. H. M. J. Triaud, I. Boisse, F. Bouchy, M. Gillon and G. Hébrard

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 423, issue 2, pages 1503-1520
Published in print June 2012 | ISSN: 0035-8711
Published online June 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.20973.x
Rossiter–McLaughlin effect measurements for WASP-16, WASP-25 and WASP-31*

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We present new measurements of the Rossiter–McLaughlin (RM) effect for three Wide Angle Search for transiting Planets (WASP) planetary systems, WASP-16, WASP-25 and WASP-31, from a combined analysis of their complete sets of photometric and spectroscopic data. We find a low-amplitude RM effect for WASP-16 (Teff= 5700 ± 150 K), suggesting that the star is a slow rotator and thus of an advanced age, and obtain a projected alignment angle of . For WASP-25 (Teff= 5750 ± 100 K), we detect a projected spin–orbit angle of λ= 14°.6 ± 6°.7. WASP-31 (Teff= 6300 ± 100 K) is found to be well aligned, with a projected spin–orbit angle of λ= 2°.8 ± 3°.1. A circular orbit is consistent with the data for all three systems, in agreement with their respective discovery papers. We consider the results for these systems in the context of the ensemble of RM measurements made to date. We find that whilst WASP-16 fits the hypothesis of Winn et al. that ‘cool’ stars (Teff < 6250 K) are preferentially aligned, WASP-31 has little impact on the proposed trend. We bring the total distribution of the true spin–orbit alignment angle, ψ, up to date, noting that recent results have improved the agreement with the theory of Fabrycky & Tremaine at mid-range angles. We also suggest a new test for judging misalignment using the Bayesian information criterion, according to which WASP-25 b’s orbit should be considered to be aligned.

Keywords: techniques: radial velocities; stars: individual: WASP-16; stars: individual: WASP-25; stars: individual: WASP-31; planetary systems

Journal Article.  11652 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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