A window on exoplanet dynamical histories

Rossiter-McLaughlin observations of WASP-13b and WASP-32b

R. D. Brothwell*, C. A. Watson, G. Hébrard, A. H M J Triaud, H. M. Cegla, A. Santerne, E. Hébrard, D. R. Anderson, D. Pollacco, E. K. Simpson, F. Bouchy, D. J A Brown, Y. Gómez Maqueo Chew, A. Collier Cameron, D. J. Armstrong, S. C C Barros, J. Bento, J. Bochinski, V. Burwitz, R. Busuttil & 25 others 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. Rodríguez, D. Ségransan, I. Skillen, B. Smalley, K. G. Stassun, S. Udry, R. G. West, P. J. Wheatley

*Corresponding author for this work

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Abstract

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 (λ). WASP-13b and WASP-32b both have prograde orbits and are consistent with alignment with measured sky-projected angles of λ =8°-12+13 and λ = -2°-19+17, 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 Super WASP 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* = 90° 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 = 11° ± 14°. 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.

Original languageEnglish
Article numberstu520
Pages (from-to)3392-3401
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Volume440
Issue number4
DOIs
Publication statusPublished - 2014

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    Brothwell, R. D., Watson, C. A., Hébrard, G., Triaud, A. H. M. J., Cegla, H. M., Santerne, A., ... 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, 440(4), 3392-3401. [stu520]. https://doi.org/10.1093/mnras/stu520