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Using Lyman-Alpha Transits to Constrain Models of Atmospheric Escape

Presentation #102.365 in the session Poster Session.

Published onJun 20, 2022
Using Lyman-Alpha Transits to Constrain Models of Atmospheric Escape

In the past decade it has become clear that atmospheric escape plays a significant role in the evolution of exoplanets. Lyman-Alpha transit spectroscopy is one of the most successful methods used to observe atmospheric escape. However due to the lack of a fundamental model describing how outflows yield a transit, it has been impossible to use them to conclusively measure atmospheric escape parameters.

One of the major problems is that the absorption of Lyman-Alpha photons in the interstellar medium makes meaningful transit detections only available in the line wings of the spectrum. 3D hydrodynamics simulations show that the outflow observed in these line wings is determined by the interaction of the escaping planetary gas and the circumstellar environment. These have been somewhat successful in reproducing the features seen in observations, however due to computational constraints of running 3D simulations it is not possible to run these over a large range of parameters in order to do a proper fit to observations. This is especially important as key parameters such as the stellar wind and EUV output of stars are poorly constrained.

In this talk, I will present a semi-analytic model of the interaction between the escaping gas and the circumstellar environment motivated by the results of 3D hydrodynamics simulations which (1) approximates the outflow to the required level of accuracy to compare to observations and (2) is computationally light enough to perform a rigorous parameter study in order to constrain important escape parameters and models of atmospheric escape. Using this model to compare to real systems undergoing atmospheric escape, such as GJ436b, I will show how one can accurately measure the launch velocity of the gas, a key discriminant between escape models such as photoevaporation and core-powered mass loss.

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