Sigma Geminorum (K1 III + ?) - Variability of the ultraviolet emission lines near conjunction

Far-ultraviolet IUE echelle spectra of the moderate-period RS CVn system Sigma Geminorum (K1 III + ?) are reported. Despite the location of the red-giant primary of Sigma Gem in a portion of the H-R diagram where cool stellar winds are common, no evidence for circumstellar absorption features or blueward asymmetries is found in the chromospheric O I (or Mg I and Mg II) 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 likely were produced by the rotation of a large-scale active region (Fried et al., 1983) off the visible hemisphere of the primary.