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Astron. Astrophys. 322, 167-174 (1997)


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X-ray properties of bright OB-type stars detected in the ROSAT all-sky survey

T.W. Berghöfer * 1, 2, J.H.M.M. Schmitt 1, R. Danner 1, 3 and J.P. Cassinelli 4

1 Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstr, 1, D-85740 Garching, Germany
2 Center for EUV Astrophysics, 2150 Kittredge Street, University of California, Berkeley, CA 94720, USA
3 Division of Physics, Mathematics, and Astronomy, Caltech 105-24, Pasadena, CA 91125, USA
4 University of Wisconsin - Madison, Department of Astronomy, 475 North Charter Street, Madison, WI 53706-1582, USA

Received 17 July 1996 / Accepted 26 November 1996

Abstract

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 (Berghöfer, Schmitt & Cassinelli 1996).

We demonstrate that the "canonical" relation between X-ray and total luminosity of [FORMULA] 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.

Key words: stars: early-type – X-rays: stars – stars: mass loss

* On the leave to: Center for EUV Astrophysics

Send offprint requests to: T.W. Berghöfer

© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998

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