Issue |
A&A
Volume 523, November-December 2010
|
|
---|---|---|
Article Number | A92 | |
Number of page(s) | 39 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361/200913570 | |
Published online | 18 November 2010 |
The X-ray source content of the XMM-Newton Galactic plane survey⋆
1
CNRS, Université de Strasbourg, Observatoire Astronomique, 11 rue de
l’Université,
67000
Strasbourg,
France
e-mail: christian.motch@astro.unistra.fr
2 Department of Physics and Astronomy, University of Leicester,
LE1 7RH, UK
3
Mullard Space Science Laboratory, University College London,
Holmbury St. Mary, Dorking, RH5
6 NT Surrey,
UK
4
Instituto de Fìsica de Cantabria (CSIC-UC),
39005
Santander,
Spain
5
Centre d’Étude Spatiale des Rayonnements, 9 avenue du Colonel
Roche, 31028
Toulouse Cedex 4,
France
6
Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482
Potsdam,
Germany
7
Departamento de Física, Ingeniería de Sistemas y Teoría de la
Señal, Universidad de Alicante, Apdo. 99, 03080
Alicante,
Spain
Received: 29 October 2009
Accepted: 2 July 2010
We report the results of an optical campaign carried out by the XMM-Newton Survey Science Centre with the specific goal of identifying the brightest X-ray sources in the XMM-Newton Galactic plane survey. In addition to photometric and spectroscopic observations obtained at the ESO-VLT and ESO-3.6 m, we used cross-correlations with the 2XMMi, USNO-B1.0, 2MASS, and GLIMPSE catalogues to advance the identification process. Active coronae account for 16 of the 30 positively or tentatively identified X-ray sources and exhibit the softest X-ray spectra. Many of the identified hard X-ray sources are associated with massive stars, possible members of binary systems and emitting at intermediate X-ray luminosities of 1032−34 erg s-1. Among these are (i) a very absorbed, likely hyper-luminous star with X-ray/optical spectra and luminosities comparable to those of η Carina; (ii) a new X-ray-selected WN8 Wolf-Rayet star in which most of the X-ray emission probably arises from wind collision in a binary; (iii) a new Be/X-ray star belonging to the growing class of γ-Cas analogues; and (iv) a possible supergiant X-ray binary of the kind discovered recently by INTEGRAL. One of the sources, XGPS-25, has a counterpart of moderate optical luminosity that exhibits HeII λ4686 and Bowen CIII-NIII emission lines, suggesting that this may be a quiescent or X-ray shielded low mass X-ray binary, although its X-ray properties might also be consistent with a rare kind of cataclysmic variable (CV). We also report the discovery of three new CVs, one of which is a likely magnetic system displaying strong X-ray variability. The soft (0.4–2.0 keV) band log N(>S) − log S curve is completely dominated by active stars in the flux range of 1 × 10-13 to 1 × 10-14 erg cm-2 s-1. Several active coronae are also detected above 2 keV suggesting that the population of RS CVn binaries contributes significantly to the hard X-ray source population. In total, we are able to identify a large fraction of the hard (2–10 keV) X-ray sources in the flux range of 1 × 10-12 to 1 × 10-13 erg cm-2 s-1 with Galactic objects at a rate consistent with what is expected for the Galactic contribution alone.
Key words: X-rays: binaries / X-rays: stars / surveys / binaries: close
Tables 9–11 and Figs. 32, 33 are only available in electronic form at http://www.aanda.org
© ESO, 2010
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