UC Santa Barbara

An inquiry into atmospheric escape driven by photoionization. We begin with a brief survey of the relevant historical development of atmospheric escape, spanning from the origins of kinetic theory to the age of exoplanets. Collisional mechanisms justifying the continuum assumption, central to the hydrodynamic framework, are scrutinized. Given the inherent presence of ions in photoionized outflows, we argue for the pervasive application of the hydrodynamic framework. Prefatory investigation of the multifrequency problem is undertaken. Results uncover notable differences from those invoking the monochromatic approximation. Notably, outflows are cooler and slower, yet denser and of higher mass-loss rates. Moreover, of importance to observations, the outflows are less ionized near the optical planetary radius and more ionized further from the planet. Supplementary to these results is our detailed procedure for generating synthetic observations.

To enable both expedited and detailed examination of the problem, a one-dimensional and three-dimensional model are prescribed. The one-dimensional modeling should provide the wider community with access to inexpensive and accurate results. On the other hand, the three-dimensional modeling can be used for precise exploration of more complicated physics. Unique to the three-dimensional results are the inclusion of asymmetric heating, the Coriolis force, and stellar winds. The large-scale morphology of three-dimensional outflows is elucidated. Energetic arguments for the extent of the outflow are presented, along with the prediction of a Coriolis shock. The consequences of varying stellar wind strengths are explored. Results predict a yet unseen, and unsearched for, transitory pretransit signal.