X-RAY-PROPERTIES OF BRIGHT OB-TYPE STARS DETECTED IN THE ROSAT ALL-SKY SURVEY

The ROSAT all-sky survey has been used to study the X-ray properties f or 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 (Berghofer, Sch mitt st Cassinelli 1996). We demonstrate that the ''canonical'' relati on between X-ray and total luminosity of L-x/L-Bol approximate to 10(- 7) valid for O-type stars extends among the early B-type stars down to a spectral type B1-B1.5;for stars ofluminosity classes I and II the s pectral type B1 defines a dividing line for early-type star X-ray emis sion. We discuss the X-ray properties of X-ray detected B2-B9 stars (L C III-V) in the context of possible companions. We also compare our re sults to the results obtained from Einstein Observatory data and ROSAT pointed observations. We show for our sample of stars that X-ray vari ability is generally not common for O-type stars as well as early B-ty pe stars.