Large-scale Wind Structures in OB Supergiants: a Search for Rotationally Modulated Halpha variability

We present preliminary results of a long-term spectroscopic monitoring of a sample of bright OB-supergiants aimed at establishing the incidence of co-rotating, large-scale wind structures by detecting rotationally modulated variability in H. Dramatic line-profile variations operating on a daily (and in some cases on a hourly) timescale are observed. A detailed period analysis has been so far carried out for 2 stars, and revealed in both cases the existence of cyclical H variations consistent with rotational modulation. In the case of HD 14134, the same periodicity is found in the contemporaneous light curve.