Towards an Understanding of Radial Velocity Shift in Uv Spectra of Symbiotic Stars

Abstract

A systematic redshift of high ionization resonance emission lines relative to the intercombination lines was found by Friedjung et al. (1883, A & A126, 4071983) in the UV spectra of a number of symbiotic binaries. The interpretation was not then clear. We present a study of archival IUE and GHRS/HST spectra of the symbiotic binary CI Cyg. The shift varies during the orbital cycle which can be understood in terms of the presence of strong circum-binary line absorption formed in an outer expanding region.