Late-Type Ca II Emission-Line Stars in the Southern Hemisphere

Abstract

The results of a photometric and spectroscopic study of twenty-three late-type southern stars with strong Ca II H and K emission are presented.The presence of photometric variability, with similar properties to the photometric wave phenomenon seen in the RS Canum Venaticorum binaries, is noted in thirteen of the fifteen stars for which extensive photometry was obtained.Of twenty stars for which high-resolution radial velocity measurements were obtained, ten are found to be single-lined and seven are found to be double-lined spectroscopic binaries.Orbital periods are determined for eight previously-unknown binaries.The periods range from 0.66 up to 53.9 days. ca II H and K spectra of ten of the program stars yield line surface fluxes in the range in the H and·K emission cores. The high proportion of single-lined RS CVn binaries in the sample is discussed in terms of selection effects.The space density of RS CVn systems with mass ratios less than q ~ 0.8 is found to be at least equal to that of the q ~ 0.8 systems. This implies a total space density of at systems in the Galactic plane is found to be 1.9 x 10 pc by this method, in reasonable agreement with the observed .value.ii CONTENTS