TERMINAL VELOCITIES OF WOLF-RAYET WINDS FROM INFRARED HE-I LINES

We have observed 1- and 2-mum spectra covering the He I 2s-2p triplet and singlet lines in a sample of Wolf-Rayet stars. Most of the He I li nes have P Cygni profiles, which are fitted using the SEI (Sobolev wit h exact integration) method to derive terminal velocities. From our ob servations of 41 stars, the He I velocities are only about 70 per cent of those measured at the violet edges of the P Cygni profiles of the C IV and Si IV resonance lines, but are in good agreement with those m easured at the greatest displacements of the saturated absorption trou ghs in these fines (v(black)). We discuss the advantages of the infrar ed method, and also the influence of binarity on the relation between the measured displacement velocities and the stars' terminal wind velo cities. For 18 stars not accessible to the IUE, these are the first ac curate values for the terminal velocities of their winds. The analysis of the He I profiles reveals differences in the radial structure of t he winds between stars of the same subtype and having similar terminal velocities.