Migrating optical depth enhancements in the UV wind lines of the WolfRayet star HD 93131.

Abstract

We report on the first identification of migrating opacity enhancements in the ultraviolet wind-lines of a Wolf-Rayet star. Systematic variability is identified in the He II lambda 1640 P Cygni profiles HD 93131 (WN 7), and is interpreted in terms of the formation and blueward migration of discrete absorption features. The properties of the features, including their formation at intermediate velocities, their progression, and the observed slow accelerations, are reminiscent of those determined for O-type stars. These data may therefore provide evidence for similarities in the mechanisms responsible for intrinsic wind variability in both classes of stars, and we discuss in particular the role of instabilities in radiatively driven winds.