OBSERVATIONS OF STRUCTURE OF THE STELLAR WIND OF HD-152408

We report on the presence of substantial, low-velocity stellar wind st ructure in the extreme O supergiant HD 152408, based on optical spectr oscopic time-series observations. Systematic variations in the form of migrating optical depth enhancements occur in the absorption trough o f the He I lambda 5876 P Cygni profile. These variations start deep in the stellar wind, slowly accelerate bluewards to greater than or equa l to 0.5 v(infinity) over similar to 1-2 days, and recur at intervals of about 1 day. Sympathetic variations are apparent in the Balmer emis sion lines. The observations provide constraints on the stability of t he low-velocity stellar wind regime, and indicate the presence of larg e-amplitude perturbations at great depths in the outflow.