Magnetically confined wind shock

Abstract

Many stars across all classes possess strong enough magnetic fields to influence dynamical flow of material off the stellar surface. For the case of massive stars (O and B types), about 10\% of them harbour strong, globally ordered (mostly dipolar) magnetic fields. The trapping and channeling of their stellar winds in closed magnetic loops leads to {\it magnetically confined wind shocks} (MCWS), with pre-shock flow speeds that are some fraction of the wind terminal speed that can be a few thousand km s$^{-1}$. These shocks generate hot plasma, a source of X-rays. In the last decade, several developments took place, notably the determination of the hot plasma properties for a large sample of objects using \xmm\ and \ch, as well as fully self-consistent MHD modelling and the identification of shock retreat effects in weak winds. In addition, these objects are often sources of H$\alpha$ emission which is controlled by either sufficiently high mass loss rate or centrifugal breakout. Here we review the theoretical aspects of such magnetic massive star wind dynamics.