Hα spectroscopy of the unusual binary V Sagittae

We present high-quality spectra of the Ha emission line of the nova-like variable V Sge, obtained during a photometric bright state during 1986 July. The profiles have several components, including (1) a very broad, flat-topped emission line that forms in the optically thin wind of one of the stars, (2) a central, narrow peak that probably originates in a circumbinary shell, and (3) a moving component that attains an extreme velocity of approach just prior to secondary eclipse (when the brighter and lower mass Roche lobe-filling primary star is in the foreground). We review models for the emission based on the expected collision of the stellar winds of both stars, and suggest that the moving component originates in a high-density region that extends from between the stars to above the leading hemisphere of the primary. The example of V Sge shows that interacting binaries may cease mass transfer in favor of mass ejection from the system at some stage in their evolution.