Model Atmospheres for Irradiated Stars in pre-Cataclysmic Variables

Abstract

Model atmospheres have been computed for M dwarfs that are strongly irradiated by nearby hot companions. A variety of primary and secondary spectral types are explored in addition to models specific to four known systems: GD 245, NN Ser, AA Dor, and UU Sge. This work demonstrates that a dramatic temperature inversion is possible on at least one hemisphere of an irradiated M dwarf and the emergent spectrum will be significantly different from an isolated M dwarf or a black body flux distribution. For the first time, synthetic spectra suitable for direct comparison to high-resolution observations of irradiated M dwarfs in non-mass transferring post-common envelope binaries are presented. The effects of departures from local thermodynamic equilibrium on the Balmer line profiles are also discussed.