Probing the Landscape of Sub-Jovian Planets around A-type Stars with TESS

Nearly all known exoplanets orbit stars later than spectral type A, and the few known planets orbiting A-type stars are larger than Jupiter. Using the Transiting Exoplanet Survey Satellite (TESS) and various ground-based telescopes, we have begun to characterize the population of planets smaller than Jupiter around these hot stars. We present early results from this initiative: (1) the first discovery of a warm Neptune orbiting an A-type star, and (2) a strong tendency for hot Neptune candidates to be false positives. These suggest a dearth of Neptune-size planets at short orbital periods, similar to the “hot Neptune desert” observed around cooler stars. This desert is believed to be due to photoevaporation of planetary atmospheres driven by stellar X-ray and extreme ultraviolet (XUV) photons. However, because most A-type stars lack coronae and therefore emit negligibly in the XUV, a different mechanism must be responsible for the trend we are observing. We explore other explanations for this finding, ranging from photoevaporation driven by less energetic photons to high-eccentricity migration. This work is supported by FINESST Award 80NSSC20K1549 (FI: Steven Giacalone).