Stellar Lyman-Alpha Emission and the Local Interstellar Medium

Abstract

The UV spectra now available in the IUE archives have been systematically searched for the presence of Lyman-alpha emission in late-type stars. The results provide the first survey of the behavior of the Ly-alpha emission line across most of the cool half of the H-R diagram. The normalized Ly-alpha emission flux is strongest in the chromospherically active RS CVn stars and in the dMe stars. The range of normalized flux values is much smaller among F-type stars than in stars of later spectral type. A dropoff appears in the flux levels of stars at B-V less than 0.30 mag. The measurements are used to search for evidence of possible high column density clouds in the local ISM. The cloud previously identified toward Alpha Oph may be seen in the reduced flux observed toward Beta Oph.