Lyman-alpha and MG II H and K fluxes in a sample of dwarf M stars.

Abstract

Ly-alpha and Mg II fluxes are given for a group of M dwarfs. The Ly-alpha and Mg II lines were extracted from low resolution spectra taken with the IUE satellite. The Ly-alpha line is shown to be an important source of radiative losses in dMe chromospheres, being at least a factor of two more important than Mg II. Overall it contributes approximately 25 percent of the total chromospheric losses, about the same as the more commonly observed H-alpha line. In order to have approximately equal contributions from these lines, one requires either a plateau region in the lower transition region or different filling factors for the two lines. In dM stars, Ly-alpha is approximately the same magnitude as Mg II.