GLOBAL X-RAY PROPERTIES OF THE O AND B STARS IN CARINA
- GAPHE, Departement AGO, Universite de Liege, Allee du 6 Aout 17, Bat. B5C, B4000 Liege (Belgium)
- Department of Astronomy and Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park, PA 16802 (United States)
- Institute for Physics and Astronomy, Universitaet Potsdam, 14476 Potsdam (Germany)
- Swarthmore College Department of Physics and Astronomy, 500 College Avenue, Swarthmore, PA 19081 (United States)
- CRESST and X-ray Astrophysics Laboratory, NASA/GSFC, Greenbelt, MD 20771 (United States)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
- Department of Geology and Astronomy, West Chester University, West Chester, PA 19383 (United States)
- Departement de Physique, Universite de Montreal, Succursale Centre-Ville, Montreal, QC, H3C 3J7 (Canada)
- School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom)
- Penn State Worthington Scranton, 120 Ridge View Drive, Dunmore, PA 18512 (United States)
The key empirical property of the X-ray emission from O stars is a strong correlation between the bolometric and X-ray luminosities. In the framework of the Chandra Carina Complex Project, 129 O and B stars have been detected as X-ray sources; 78 of those, all with spectral type earlier than B3, have enough counts for at least a rough X-ray spectral characterization. This leads to an estimate of the L{sub X}-L{sub BOL} ratio for an exceptional number of 60 O stars belonging to the same region and triples the number of Carina massive stars studied spectroscopically in X-rays. The derived log(L{sub X}/L{sub BOL}) is -7.26 for single objects, with a dispersion of only 0.21 dex. Using the properties of hot massive stars listed in the literature, we compare the X-ray luminosities of different types of objects. In the case of O stars, the L{sub X}-L{sub BOL} ratios are similar for bright and faint objects, as well as for stars of different luminosity classes or spectral types. Binaries appear only slightly harder and slightly more luminous in X-rays than single objects; the differences are not formally significant (at the 1% level), except for the L{sub X}-L{sub BOL} ratio in the medium (1.0-2.5 keV) energy band. Weak-wind objects have similar X-ray luminosities but they display slightly softer spectra compared with 'normal' O stars with the same bolometric luminosity. Discarding three overluminous objects, we find a very shallow trend of harder emission in brighter objects. The properties of the few B stars bright enough to yield some spectral information appear to be different overall (constant X-ray luminosities, harder spectra), hinting that another mechanism for producing X-rays, besides wind shocks, might be at work. However, it must be stressed that the earliest and X-ray brightest among these few detected objects are similar to the latest O stars, suggesting a possibly smooth transition between the two processes.
- OSTI ID:
- 21562680
- Journal Information:
- Astrophysical Journal, Supplement Series, Vol. 194, Issue 1; Other Information: DOI: 10.1088/0067-0049/194/1/7; ISSN 0067-0049
- Country of Publication:
- United States
- Language:
- English
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