Magnetically confined winds of hot stars

Abstract
We discuss the interplay between radiatively driven winds and magnetic fields in hot stars. In late main sequence B stars, radiatively driven winds are likely to occur but with a mass loss rate strongly affected by the magnetic field structure at the stellar surface. Away from the stellar surface, the interaction of a radiatively driven wind with a dipolar magnetic field lead to the formation of a large magnetosphere consisting of an extended hot postshock region as well as a dense cooling disk forming near the magnetic equator (Magnetically Confined Wind Shock Model, MCWS). In the context of this model, we try to interpret an extensive set of observations (X-ray, UV and optical data) available for the O7V star Ori C as well as the pulsating B star Cep. We finally show how observations of X-ray lines with the XMM or Chandra spacecrafts could help us to obtain a clearer picture of the interaction between magnetic fields and the winds of hot stars.