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A. W. Fullerton (U. Victoria / JHU), D. L. Massa (Raytheon ITSS / GSFC), I. D. Howarth (UCL), S. P. Owocki (Bartol, U. Delaware), R. K. Prinja, A. J. Willis (UCL)
We present results from an 18-day campaign to monitor stellar wind variability in {Sk~-67{\arcdeg}166} (HDE~269698), an O4~If+ star in the Large Magellanic Cloud, with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. Optical depth enhancements that progress from blue to red through the absorption trough are prominent in all unsaturated P~Cygni profiles, particularly the resonance doublets of {\ion{S}{4}} and {\ion{P}{5}}. Related variability is evident in the resonance lines of {\ion{S}{6}} and {\ion{O}{6}}. The variations are qualitatively similar to those observed in the {\ion{Si}{4}} wind lines of the Galactic supergiant \zeta~Puppis [O4~I(n)f] during a 16-day monitoring campaign with IUE. However, the FUSE observations contain more diagnostic information about the nature of the structures responsible for the observed variability. In particular, the relative amplitudes of the variations in {\ion{S}{4}} and {\ion{S}{6}} provide the first empirical constraint on the ionization equilibrium of these structures in an O star wind, while the variability of {\ion{O}{6}} traces the distribution of very hot gas.
This work is based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer. FUSE is operated for NASA by the Johns Hopkins University under NASA contract NAS5-32985.