X-ray heating of the quiescent chromospheres of dMe stars

The Einstein Observatory has found dwarf M stars to be particularly intense X-ray sources, with an X-ray luminosity that may be as large as 10% of the stellar visual luminosity. The present paper discusses the potential contributions of the coronal X-ray flux to the heating of dMe star chromospheres. The components of quiescent chromospheric heating by a coronal X-ray source are examined, with attention given to X-ray source characteristics, X-ray transfer, and the atmospheric energy balance. A model chromosphere for dMe stars is constructed based on a radiative equilibrium model photosphere with solar abundances. It is shown that X-ray heating may account for both the quantity and distribution of radiative losses from the chromosphere of a quiescent dMe star, and thus may resolve the problem of the inadequacy of acoustic-wave chromospheric heating.