OPTICAL OBSERVATIONS OF LINE-PROFILE VARIABILITY IN THE WN5 STAR HD-50896

The WN5 star HD 50896 is a well known variable star but the cause of t he variations is uncertain. As part of an extensive observing campaign on HD 50896, 68 spectra were obtained with the AAT and UCL echelle sp ectrograph over three nights in January 1991. The variations seen in t he emission line profiles of HeII lambda 4686, HeII X4860, NV lambda 4 945 and NV lambda 4603, lambda 4620, sampling different regions of the wind, are described. Gross night-to-night changes are seen in the top s of all the emission lines, with the pattern of variability being dif ferent for each line, as a consequence of the different line formation regions. The edges of the emission line profiles are seen to shift bu t not in a systematic way, as expected for binary motion. In terms of hourly variations which monitor the propagation of instabilities in th e wind, distinct 'blobs' are seen moving outwards through the emission line profiles of the HeII lines but are absent in NV lambda 4945. Thi s appears to indicate that, at least for the epoch of these observatio ns, the instabilities develop farther out in the wind than the NV form ation region and may well rule out photospheric-inducedced wind instab ilities.