EDP Sciences
Free access
Volume 445, Number 3, January III 2006
Page(s) 1093 - 1097
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20053496

A&A 445, 1093-1097 (2006)
DOI: 10.1051/0004-6361:20053496

Evidence for colliding winds in WR 25 from XMM-Newton observations of X-ray variability

A. M. T. Pollock1 and M. F. Corcoran2, 3

1  European Space Agency, XMM-Newton Science Operations Centre, European Space Astronomy Centre, Apartado 50727, Villafranca del Castillo, 28080 Madrid, Spain
2  Laboratory for High Energy Astrophysics, Goddard Space Flight Center, Greenbelt, MD 20771, USA
3  Universities Space Research Association, 7501 Forbes Blvd, Ste 206, Seabrook, MD 20706, USA

(Received 23 May 2005 / Accepted 8 September 2005 )

The Wolf-Rayet star WR 25 in the Carina Nebula is a surprisingly bright X-ray source, and amongst the brightest WR stars in X-rays. It is a suspected binary star, though its binary nature has been a matter of controversy. We report here observations of WR 25 from the XMM-Newton archive which showed an increase in X-ray luminosity of more than a factor of two. The X-ray absorption also increased. Such a large change in X-ray output is unknown in single massive stars, though large changes in X-ray brightness are seen in binaries. The most likely explanation of the observed X-ray variability is as a result of colliding-wind emission in a moderately eccentric binary with a period of about 4 years. The next periastron passage is expected in 2007. The X-ray spectrum is similar to that of the archetype colliding-wind binary WR 140.

Key words: X-rays: stars -- stars: Wolf-Rayet -- stars: individual: WR 25 -- stars: winds, outflows -- stars: binaries: general

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