Speaker
Description
Planets on misaligned orbits around rapid rotators can experience “gravity-darkened seasons” as their orbits cross over the hot poles and cooler equators of rotationally-flattened stars. The periodically variable heating from these seasons presents a unique case for exploring how changes in stellar irradiation influence planetary atmospheric dynamics. We perform a homogeneous analysis of day-to-nightside winds on the ultra-hot Jupiters KELT-9 b and KELT-20 b, enabling the comparison of a planet experiencing gravity-darkened seasons (KELT-9 b) with a similar planet that does not (KELT-20 b). We conduct high-resolution transmission spectroscopy using two transits observed by the PEPSI spectrograph on the Large Binocular Telescope to empirically constrain supersonic ~10 km/s day-to-nightside winds traced by Fe II features in the atmosphere of KELT-9 b. Reconciling our findings with two archival HARPS-N datasets suggests multi-epoch variability ~5-8 km/s over timescales between weeks to years. In contrast, KELT-20 b’s day-to-nightside winds are less rapid (~2 km/s) and stable across four transits collectively observed by PEPSI and HARPS-N. The observed contrast of KELT-9 b’s wind variability and KELT-20 b’s stability is in accordance with our intuition on the effect of gravity-darkened seasons. A qualitative evaluation of our measured wind velocities and variability against current ultra-hot Jupiter GCMs reveals that KELT-9 b poses unique challenges for validating giant planet atmospheric models.
