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Issue A&A
Volume 402, Number 2, May I 2003
Page(s) 653 - 666
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20030119



A&A 402, 653-666 (2003)
DOI: 10.1051/0004-6361:20030119

XMM-Newton high-resolution X-ray spectroscopy of the Wolf-Rayet object WR 25 in the Carina OB1 association

A. J. J. Raassen1, 2, K. A. van der Hucht1, R. Mewe1, I. I. Antokhin3, 4, 5, G. Rauw3, J.-M. Vreux3, W. Schmutz6 and M. Güdel7

1  SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
    e-mail: a.j.j.raassen@sron.nl;k.a.van.der.hucht@sron.nl;r.mewe@sron.nl
2  Astronomical Institute Anton Pannekoek, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
    e-mail: raassen@astro.uva.nl
3  Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août, 17 Bât. B5c, 4000 Liège, Belgique
    e-mail: rauw@astro.ulg.ac.be; vreux@astro.ulg.ac.be
4  Present address: Department of Physics and Astronomy, University of Glasgow, Kelvin Building, Glasgow G12 8QQ, Scotland, UK
    e-mail: igor@astro.gla.ac.uk
5  On leave from: Sternberg Astronomical Institute, Moscow University, Universitetskij Prospect 13, Moscow 119899, Russia
6  Physikalisch-Meteorologisches Observatorium Davos, Dorfstrasse 33, 7260 Davos Dorf, Switzerland
    e-mail: w.schmutz@pmodwrc.ch
7  Paul Scherrer Institut, Würenlingen & Villigen, 5232 Villigen PSI, Switzerland
    e-mail: guedel@astro.phys.ethz.ch

(Received 26 November 2002 / Accepted 21 January 2003 )

Abstract
We report the analysis of the first high-resolution X-ray spectra of the Wolf-Rayet (WR) object WR 25 (HD 93162, WN6ha+O4f) obtained with the R eflection Grating Spectrometers (RGS) and the E uropean Photon Imaging Cameras (EPIC-MOS and  PN ) CCD spectrometers on board the XMM-Newton satellite. The spectrum exhibits bright emission lines of the H- and He-like ions of Ne, Mg, Si and S, as well as Fe XVIII to Fe XX and Fe XXV lines. Line fluxes have been measured. The RGS and EPIC spectra have been simultaneously fitted to obtain self-consistent temperatures, emission measures, and elemental abundances. Strong absorption by the dense WR stellar wind and the interstellar medium (ISM) is observed equivalent to $N_{\rm H} = 7 \times 10^{21}$ cm -2. Multi-temperature (DEM) fitting yields two dominant components around temperatures of 7.0 and 32 MK, respectively. The XMM intrinsic (i.e. unabsorbed, corrected for the stellar wind absorption and the absorption of ISM) X-ray luminosity of WR 25 is $L_{\rm x}$(0.5-10 keV) = $1.3 \times 10^{34}$ erg s -1, and $L_{\rm x}$(0.5-10 keV) = $0.85 \times 10^{34}$ erg s -1, (when correcting for the ISM only) assuming d=3.24 kpc. The obtained chemical abundances are subsolar, except for S. This may be real, but could equally well be due to a weak coupling to the continuum, which is strongly influenced by the absorption column density and the subtracted background. The expected high N-abundance, as observed in the optical wavelength region, could not be confirmed due to the strong wind absorption, blocking out its spectral signature. The presence of the Fe XXV emission-line complex at ~ 6.7 keV is argued as being indicative for colliding winds inside a WR+O binary system.


Key words: stars: individual: WR 25 -- stars: early-type -- stars: Wolf-Rayet -- stars: binaries: general -- stars: abundances -- X-rays: stars

Offprint request: A. J. J. Raassen, a.j.j.raassen@sron.nl

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