The location and X-ray emission of shocks around isolated be stars

All hot stars are observed to have X-ray emission: O stars haveL _X /L _bol 10^–7, whilst B stars' emission drops off with spectral subtype. Dynamical instability of OB star radiatively driven winds generates shocked regions which may be responsible for the bulk of the X-rays observed. The wind-compressed disc model of Bjorkman & Cassinelli (1993) presents another site for X-ray emission. The disc formed in the equatorial plane of a fast rotating Be star from equatorward drift of wind streamlines is confined on both sides by a shock which may also generate X-rays. As the X-ray emission originating from the wind shocking is ubiquitous amongst B and Be stars then the wind-compressed disc model näively predicts that Be stars should generate more X-rays than B stars of equivalent spectral subtype.The X-ray emission from the shocks confining compression discs has been calculated and compared to a limited set of observations. The excess X-ray emission from the Be star disc shocks is found to be undetectable over the inherent wind shocking emission.