Ultraviolet Observations of Selective Wind Eclipses in gamma Velorum and Evidence for Colliding Winds
The paper presents an analysis of all IUE high-resolution spectra available in the archives of the WC8 + O9I binary system Gamma Velorum. The IUE data are supplemented by a series of FUV spectra obtained with the Copernicus satellite covering the whole orbital period. The data reveal substantial UV spectral variations confined to resonance and low-excitation lines of Si II, Si III, Si IV, C II, C III, C IV, S IV, and Fe IV. The variations are strongly dependent on orbital phase and are repeatable from one binary cycle to another. It is shown that the observed UV spectral variability of Gamma Velorum is consistent with that expected in the selective line eclipse model for the system. The paper also presents high-resolution IUE observations of V444 Cygni and CV Serpentis binaries, which show a similar pattern of phase-related spectral-line variations.