  OB stars are known to exhibit various types of wind variability, as detected
in their ultraviolet spectra, amongst which are the ubiquitous discrete
absorption components (DACs). These features have been associated with
large-scale azimuthal structures extending from the base of the wind to its
outer regions: corotating interaction regions (CIRs). There are several
competing hypotheses as to which physical processes may perturb the star's
surface and generate CIRs, including magnetic fields and non radial pulsations
(NRPs), the subjects of this paper with a particular emphasis on the former.
Although large-scale magnetic fields are ruled out, magnetic spots deserve
further investigation, both on the observational and theoretical fronts.

Solar and Stellar Astrophysics