The Detection of Wind Variability in Magellanic Cloud O Stars

We present Far Ultraviolet Spectroscopic Explorer (FUSE) spectra for three Magellanic Cloud O stars (Sk 80, Sk -67°05, and Sk -67°111) with repeated observations. The data demonstrate the capabilities of FUSE to perform time-resolved spectroscopy on extragalactic stars. The wavelength coverage of FUSE provides access to resonance lines due to less abundant species, such as sulfur, which are unsaturated in O supergiants. This allows us to examine wind variability at all velocities in resonance lines for stars with higher mass-loss rates than can be studied at longer (λ ≥ 1150 Å) wavelengths. The FUSE wavelength range also includes resonance lines from ions that bracket the expected dominant ionization stage of the wind. Our observations span 1-4 months with several densely sampled intervals of 10 hr or more. These observations reveal wind variability in all of the program stars and distinctive differences in the ionization structure and timescales of the variability. Sk -67°111 demonstrates significant wind variability on a timescale less than 10 hr, and the coolest O star (Sk -67°05) exhibits the largest variations in O VI.