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

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 ($\lambda$). WASP-13b and WASP-32b both have prograde orbits and are consistent with alignment with measured sky-projected angles of $\lambda ={8^{\circ }}_{-12}^{+13}$ and $\lambda ={-2^{\circ }}_{-19}^{+17}$, respectively. Both WASP-13 and WASP-32 have $T_{\mathrm{eff}}<6250$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\% confidence) was identified for the WASP-32 system with $P_{\mathrm{rot}}=11.6\pm 1.0$ days. This rotation period is in agreement with the predicted stellar rotation period calculated from the stellar radius, $R_{\star }$, and $v\sin i$ if a stellar inclination of $i_{\star }=90^{\circ }$ 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 $\psi =11^{\circ }\pm 14$. We conclude with a discussion on the alignment of systems around cool host stars with $T_{\mathrm{eff}}<6150$K 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.

12 pages, 4 Figures, Accepted for publication in MNRAS

References in corpus (4)

• Prospects for the Characterization and Confirmation of Transiting Exoplanets via the Rossiter-McLaughlin Effect
• WASP-1b and WASP-2b: Two new transiting exoplanets detected with SuperWASP and SOPHIE
• WASP-80b: a gas giant transiting a cool dwarf
• Analysis of spin-orbit alignment in the WASP-32, WASP-38, and HAT-P-27/WASP-40 systems

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• The study on transiting systems HAT-P-13, HAT-P-16 and WASP-32 through combining ground-based and TESS photometry