Sigma Geminorum (K1 III + ?) : variability of the ultraviolet emission lines near conjunction.

Abstract

Far-ultraviolet IUE echelle spectra are reported of the moderate-period RS CVn system σ Geminorum. Despite the location of the red giant primary of σ Gem in a portion of the H-R diagram where cool stellar winds are common, no evidence is found for circumstellar absorption features or blueward asymmetries in the chromospheric O I emission cores. However, observations on two consecutive days indicate significant changes in the profiles of high-excitation species, such as Si IV and C IV which probably were produced by the rotation off of the visible hemisphere of the primary of a large-scale magnetic active region identified in a previous photometric study.