Non - Radial Pulsations and Large - Scale Structure in Stellar Winds

Almost all early-type stars show Discrete Absorption Components (DACs) in their ultraviolet spectral lines. These can be attributed to Co-rotating Interaction Regions (CIRs): large-scale spiral-shaped structures that sweep through the stellar wind. We used the Zeus hydrodynamical code to model the CIRs. In the model, the CIRs are caused by " spots " on the stellar surface. Through the radiative acceleration these spots create fast streams in the stellar wind material. Where the fast and slow streams collide, a CIR is formed. By varying the parameters of the spots, we quantitatively fit the observed DACs in HD 64760. An important result from our work is that the spots do not rotate with the same velocity as the stellar surface. The fact that the cause of the CIRs is not fixed on the surface eliminates many potential explanations. The only remaining explanation is that the CIRs are due to the interference pattern of a number of non-radial pulsations. Structure in O-type stellar winds Many indicators exist for the presence of structure in the stellar winds of early-type stars. Here we discuss the wind structure in O and early B-type stars; structure in Wolf-Rayet stars is discussed by Gosset (these proceedings). Two types of structure are known to co-exist in the stellar wind: small-scale and large-scale. The small-scale type (clumping) has been discussed by Puls (these