1997A&A...322..167B

The ROSAT all-sky survey has been used to study the X-ray properties for all OB-type stars listed in the Yale Bright Star Catalogue. Here we present a detailed astrophysical discussion of our analysis of the X-ray properties of our complete sample of OB-type stars; a compilation of the X-ray data is provided in an accompanying paper (Berghoefer, Schmitt & Cassinelli 1996A&AS..118..481B). We demonstrate that the ``canonical'' relation between X-ray and total luminosity of L_x/L_Bol≃10^–7 valid for O-type stars extends among the early B-type stars down to a spectral type B1-B1.5; for stars of luminosity classes I and II the spectral type B1 defines a dividing line for early-type star X-ray emission. We discuss the X-ray properties of X-ray detected B2-B9 stars (LC III-V) in the context of possible companions. We also compare our results to the results obtained from Einstein Observatory data and ROSAT pointed observations. We show for our sample of stars that X-ray variability is generally not common for O-type stars as well as early B-type stars.