The spectral variability of HD 192639 and its implications for the star's wind structure

We report the analysis of an extensive set of spectroscopic data of the O(f) supergiant HD 192639. A Fourier analysis of our time-series reveals a recurrent variability with a "period" of roughly 4.8 days which is most prominent in the absorption components of the He II X 4686 and H alpha P-Cygni profiles. The same periodicity is also detected in the blue wing of several absorption lines (e.g. H beta). The variations of the absorption components correspond most probably to a cyclical modulation of the amount of stellar wind material along the line of sight towards the star. The 4.8-day period affects also the morphology of the double-peaked He II lambda 4686 and HQ. emission components, although these emission components display also variations on other (mainly longer) time scales. The most likely explanation for the 4.8-day modulation is that this cycle reflects: the stellar rotational period (or half this period). We find that the most important observational properties can be explained - at least qualitatively - by a corotating interaction region or a tilted confined corotating wind.