Computing Models of M-type Host Stars and their Panchromatic Spectral Output

 We have begun a program of computing state-of-the-art model
atmospheres from the photospheres to the coronae of M stars that are the
host stars of known exoplanets. For each model we are computing the
emergent radiation at all wavelengths that are critical for assessing
photochemistry and mass-loss from exoplanet atmospheres. In
particular, we are computing the stellar extreme ultraviolet radiation
that drives hydrodynamic mass loss from exoplanet atmospheres and is
essential for determing whether an exoplanet is habitable. The model
atmospheres are computed with the SSRPM radiative transfer/statistical
equilibrium code developed by Dr. Juan Fontenla. The code solves for the
non-LTE statistical equilibrium populations of 18,538 levels of 52 atomic
and ion species and computes the radiation from all species (435,986
spectral lines) and about 20,000,000 spectral lines of 20 diatomic species.

The first model computed in this program was for the modestly active
M1.5 V star GJ 832 by Fontenla et al. (ApJ 830, 152 (2016)). We will
report on a model for the more active M5 V star GJ 876 and compare
this model and its emergent spectrum with GJ 832. In the future, we will
compute and intercompare semi-empirical models and spectra for all
of the stars observed with the HST MUSCLES Treasury Survey, the
Mega-MUSCLES Treasury Survey, and additional stars including Proxima Cen
and Trappist-1.

This talk is dedicated to the memory of Dr. Juan Fontenla who passed
away in January 2018.

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