The Dynamical Evolution of WASP-13b and WASP-32b

A Window on Exoplanet Dynamical Histories: Rossiter-McLaughlin Observations of WASP-13b and WASP-32b

Authors:

Brothwell et al

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∘+13−12 and λ=−2∘+17−19, respectively.

Both WASP-13 and WASP-32 have Teff less than 6250K 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\% 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 vsini 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 less than 6150K by calculating the tidal dissipation timescale. We find that systems with short tidal dissipation timescales are preferentially aligned and systems with long tidal dissipation timescales have a broad range of obliquities.