A Study of the Discontinuous Drop in X-ray Emission at Spectral Type B1

B supergiants display a discontinuous drop in Xray emission along a dividingline in the HR diagram (analogous to the one for K giants) which is referred toas the bistability jump at spectral type B1. Our XMM study of the Xrayproperties on both sides of the jump have revealed several interesting results,but some uncertainties have arisen since B supergiant winds are thick to softXrays, and these winds are thought to be clumpy. We now have observationalevidence that the bistabilty jump extends to the lower luminosity B giants whichhave lower wind densities. Hence, they do not have the problems that areassociated with B supergiants. Therefore we are requesting XMM EPIC observationsof 5 B giants to broaden our understanding of the B star dividing line. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]