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Constraining spin-orbit angles photometrically using a fast, efficient transit model for oblate, gravity-darkened planet hosts

Presentation #102.232 in the session Poster Session.

Published onJun 20, 2022

Constraining spin-orbit angles photometrically using a fast, efficient transit model for oblate, gravity-darkened planet hosts

Exoplanets that transit rapidly-rotating stars are unique tools to learn about the dynamical history of such systems photometrically. Rapidly-rotating stars exhibit both oblateness and gravity darkening, where the poles are hotter and more luminous than the equator due to latitude-dependent stellar surface gravity. Both of these effects break spherical symmetry and can allow a photometric measurement of the true spin-orbit angle of the system. We create an efficient, semi-analytic transit model in the starry package that incorporates these effects. The implementation in starry is orders of magnitude faster and more precise than equivalent numerical methods and well suited to posterior inference. We test the model on a TESS light curve of WASP-33. We subtract the host’s delta-Scuti pulsations from the light curve, finding an asymmetric transit characteristic of gravity darkening. We find the projected spin orbit angle is consistent with Doppler tomography and constrain the true spin-orbit angle of the system. We note the method’s use as a complement to spectroscopic measurements that provide the projected spin-orbit angle. Space-based missions such as TESS and CHEOPS will observe transits for hundreds of early-type stars, many of which will be amenable to constraints using this method.