The Dependence of Ultraviolet Chromospheric Emission upon Rotation among Late-Type Stars

Abstract

The authors have obtained low-resolution IUE spectra of a large number of chromospherically active stars. Integrated fluxes of chromospheric and transition region emission lines have been measured. These fluxes, supplemented by published observations and measurements of IUE archival spectra, have been used to search for correlations between activity, rotation period, and Rossby number for active and normal chromosphere stars. The UV emission of the active chromosphere stars as an undifferentiated class decreases in strength with declining rotation rate but shows little if any dependence upon rotation within individual luminosity classes. For single, slowly rotating dwarf stars, there is no observational distinction between rotation-activity relations expressed in terms of normalized emission line flux versus Rossby number, and surface flux versus rotation period.