UES and IUE observations of the O9.5 V star HD 93521: non-radial pulsations, wind, and distance

We have obtained time-series spectroscopy of the rapidly rotating O9.5 V star HD 93521 during commissioning of the Utrecht Echelle Spectrograph on the William Herschel Telescope. The He I lines show wiggles at the ∼1% level, which move systematically from blue to red across the profile; by contrast, the He II lines do not show detectable variations. We interpret these characteristics as indicative of sectorial-mode non-radial pulsations coupled with significant gravity darkening, and estimate P=1.8 hours, l=−m≃9, k<0.3. The Hα and He I λ5876 A lines show emission wings, and line-profile variability which may be associated with circumstellar material