AAS 198th Meeting, June 2001
Session 45. Stellar Observations with FUSE
Display, Tuesday, June 5, 2001, 10:00am-6:30pm, Exhibit Hall

## [45.01] {\em FUSE} snap-shot survey of \ion{O}{6} wind variability in OB-type stars

N. Lehner (JHU), A.W. Fullerton (U. Victoria/JHU), D. Massa (Raytheon ITSS/GSFC), K.R. Sembach (JHU)

Although \ion{O}{6} is found in spectra of stars with temperature classes from O3 to B1, it is a superion" in the winds of those stars; i.e., it cannot be formed by the photospheric radiation field alone. It is usually thought that \ion{O}{6} is produced by ensembles of shocks embedded in the wind, which might be produced by the strong line-driven instability. Therefore, the shapes and strengths of the \ion{O}{6} lines are not determined by the stationary structure of the stellar wind, but by the distribution, strength, and variability of the shocks. To assess the possible origins of \ion{O}{6} in the winds of such stars, we undertook a snap-shot survey of repeated observations toward Galactic and Large Magellanic Cloud stars with the {\em Far Ultraviolet Spectroscopic Explorer} ({\em FUSE}). The data consist of 2 or 3 observations spaced unequally over a variety of time scales, typically a few days to several months. The preliminary results of this survey show that the \ion{O}{6} wind variability, far from being an anomaly, is a normal characteristic, as for the other unsaturated wind lines. The strengths and shapes of the variations can be very different from star to star. The {\em FUSE} bandpass allows us to observe simultaneously other ions, such as \ion{S}{4}, and a systematic comparison is presented between \ion{O}{6} and \ion{S}{4}. We briefly discuss the implications that the \ion{O}{6} wind variability can have on interstellar \ion{O}{6} measurements.

This work is based on data obtained for the Guaranteed Time Team by the NASA-CNES-CSA FUSE mission operated by the Johns Hopkins University. Financial support to U. S. participants has been provided by NASA contract NAS5-32985.