A hydrodynamic study of radiative cooling and escape of metal species in hot Jupiter atmospheres

The heating by photo-ionization in the thermosphere of short-period exoplanets can drive hydrodynamic escape, which is key to understanding the evolution of the planet atmosphere and explaining the atmospheric measurements. Besides powering the atmosphere escape, the energy deposited by EUV photons from the host star can also be radiated away through collisional excited atomic spectral lines, leading the mass loss rate to fall significantly below the energy limit. Recent observations have detected evidence of atomic Mg and Fe absorptions in the NUV transmission spectrum of hot Jupiter WASP-121b and HD 209458b. Studying the signature of these atomic lines not only can reveal the structure of the upper atmosphere, but also constrain the radiative cooling rates. These lines will also be detectable by the Colorado Ultraviolet Transit Experiment (CUTE) satellite that will monitor extrasolar giant planets for evidence of mass loss and magnetic fields. In this work, we expand the capability of the exoplanet hydrodynamic atmosphere code of Koskinen et al. (2013) to calculate processes of atomic metal species and compare the results with available observations.