287

Yapeng Zhang

High-resolution transmission spectroscopy of ultra-hot Jupiters: the exospheric origin of Fe II absorption

Ultra-hot Jupiters (UHJs), rendering the hottest planetary atmospheres, offer great opportunities of detailed characterisation with high-resolution spectroscopy. The extremely irradiated atmospheres are interesting laboratories for studying the mass loss through hydrodynamic escapes. We present the analysis on the optical transmission spectrum of a recently discovered ultra-hot Jupiter MASCARA-4b using two transit observations taken with the high-resolution spectrograph ESPRESSO at the VLT, and search for atomic absorption features in the atmosphere. We detected planetary absorption by a profusion of species such as H, Na, Mg, Ca, Ca II, Cr, Fe, Fe II. The absorption strength of Fe II significantly exceeds the prediction from a hydrostatic atmospheric model, which is also commonly observed in other UHJs. We attribute this to the presence of Fe II in the extended exosphere as a consequence of hydrodynamic outflows. In exploration of trends within the UHJ population, we find a positive correlation of the absorption strength between Fe II and Halpha, which further indicates the exospheric origin of the Fe II absorption, showing the potential of both species as probes for the mass loss process of strongly irradiated planets.