Magnetic OB stars, and normal B stars
Magnetically channeled wind-shock models are promising (q1 Ori C, perhaps t Sco): Schulz (2003) has shown that O stars have these X-ray signatures for less than 1 million years on the main sequence
Normal B stars (like b Cru, B0.5 IV and e CMa B2 II) have very soft X-ray spectra and narrow lines: wind shocks if the X-ray wind isnŐt moving very fast? Magnetically channeled wind shocks if the shocks arenŐt very strong? Dynamo-driven coronae if our understanding of dynamos is incompleteÉ