[en] 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[/SUB]-L [SUB]BOL[/SUB] 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[/SUB]/L [SUB]BOL[/SUB]) 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[/SUB]-L [SUB]BOL[/SUB] 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[/SUB]-L [SUB]BOL[/SUB] 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.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Nazé, Yaël ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Astrophysique observationnelle (sol et espace)
Broos, P. S.; Department of Astronomy & Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park, PA 16802, USA
Oskinova, L.; Institute for Physics and Astronomy, Universität Potsdam, 14476 Potsdam, Germany
Townsley, L. K.; Department of Astronomy & Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park, PA 16802, USA
Cohen, D.; Swarthmore College Department of Physics and Astronomy, 500 College Avenue, Swarthmore, PA 19081, USA
Corcoran, M. F.; CRESST and X-ray Astrophysics Laboratory, NASA/GSFC, Greenbelt, MD 20771, USA ; Universities Space Research Association, 10211 Wincopin Circle, Suite 500 Columbia, MD 21044, USA
Evans, N. R.; Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
Gagné, M.; Department of Geology and Astronomy, West Chester University, West Chester, PA 19383, USA
Moffat, A. F. J.; Département de Physique, Université de Montréal, Succursale Centre-Ville, Montréal, QC, H3C 3J7, Canada ; Centre de recherche en astrophysique du Québec, Canada
Pittard, J. M.; School of Physics and Astronomy, The University of Leeds, Leeds LS2 9JT, UK
Rauw, Grégor ; GAPHE, Département AGO, Université de Liège, Allée du 6 Août 17, Bat. B5C, B4000 Liège, Belgium
ud-Doula, A.; Penn State Worthington Scranton, 120 Ridge View Drive, Dunmore, PA 18512, USA
Walborn, N. R.; Space Telescope Science Institute, 3700 Martin Drive, Baltimore, MD 21218, USA
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