Building Reliable Models of M Dwarf Chromospheres: The Spectral Diagnostics

Abstract

As part of an ongoing project to study how reliable are the chromospheric models constructed semiempirically to fit the chromospheric spectrum of cold stars, in this paper we study how changes in the assumed chromospheric structure of dM and dMe stars affect the emitted spectrum. In this way, we study if a given set of features can wholly determine the atmospheric structure, how large are the indeterminations in the atmospheric parameters deduced, and to what extent the atmospheric model computed can be considered unique. We find that the profiles of the Ca II K line or the Na D lines can be used to determine the structure of the Tmin region and that the Hα profile can provide good information on the structure of the chromosphere. The Lyα flux, in turn, can be used to constrain the position of the transition region.