The First Dedicated Survey of Atmospheric Escape from Planets Orbiting F Stars

Abstract Hydrodynamic escape can strip the envelopes of close-in exoplanets, but most observations of atmospheric mass loss to date have been confined to planets orbiting K and M dwarfs. A growing body of detections of atmospheric escape from planets orbiting early-type stars indicates that they may have significantly stronger and more extended outflows than planets orbiting cooler stars. However, it is unclear whether this limited sample of planets is representative of all gas giants orbiting early-type stars. Motivated by this question, we initiated the first dedicated survey of atmospheric escape from gas giants orbiting F stars in order to understand how their distinct radiation environments shape planetary outflows. We observed 10 transits of six planets in an ultra-narrowband filter centered on the metastable helium line using Palomar/WIRC. We report strong (>3 σ ) detections of atmospheric escape for WASP-12 b and WASP-180 A b, tentative (>2 σ ) detections for WASP-93 b and HAT-P-8 b, and nondetections for WASP-103 b and KELT-7 b. We fit these measurements with a 1D Parker wind model to derive corresponding mass-loss rates, and combine our results with literature measurements to obtain an updated picture of mass loss from planets orbiting early-type stars. Our results indicate that the observed variation in mass-loss rates can be explained by a combination of Roche filling factor and X-ray and extreme ultraviolet luminosity, and disfavors near-UV-driven escape models.