Stratification of the Extended Atmosphere of the Wolf-Rayet Component of V444 Cygni

Abstract

The authors have obtained ultraviolet spectra covering both eclipses of V444 Cyg. Striking atmospheric eclipses, of up to 0.7 mag in depth, were detected in individual strong lines as well as over large ranges of the continuum shortward of 1500 Å. The continuum in the 1560 - 1900 Å range is produced by electron scattering. At shorter wavelengths extra opacity due to ions in shells centered on the WN 5 component causes marked phase dependence. The primary source of this opacity seems to be excited multiplets of Fe V. Some of these shells extend to well beyond the distance to the O6 component. The terminal velocity of the WN 5 wind, as determined from the blue edges of Si IV and C IV resonance lines, is 2550±200 km s^-1.