The Drop in X-ray Flux at Spectral Type B1: Evidence for a B-Star Dividing Line

All B star luminosity classes show a substantial drop in their Xray emissionbetween spectral type B1 and B2 suggesting an HR diagram Bstar dividing linesomewhat analogous to the one for K giants. This emission appears to be relatedto the bistability jump at spectral type B1. But our analyses of B supergiantand giant XMM data revealed several interesting and unexpected results that donot support theoretical predictions. There seems to be a fundamental, unknown,underlying process at work in this spectral region. We now wish to extent ourstudy by requesting XMM EPIC observations of 4 B main sequence stars and 2additional B giants to help us explain the abrupt Xray changes that areoccurring in this intriguing region of the HR diagram. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]