winds

A subpopulation (~9%) of hot (OB) stars exhibit strong (B~100-10,000 G), large-scale (often predominantly dipolar) magnetic fields that channel their stellar wind outflows into circumstellar magnetospheres. For young, rapidly rotating B-stars that have not yet been spun down by wind-magnetic braking, wind material can be trapped between the Kepler co-rotation radius (RK) and the Alfven radius (RA), forming then a “Centrifugal Magnetosphere” (CM), with density set at the critical level for “Centrifugal Breakout” (CBO) against the confining magnetic tension. This talk discusses how such CBO controls both the onset and strength of observed H-alpha emission, while the energetics of the associated CBO-driven magnetic reconnection match well the observed scalings of a non-thermal, circularly polarized radio emission from such stars .