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

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 reflection grating spectrometers (rgs )a nd theeuropean photon imaging cameras (epic-mos and pn) ccd spectrometers on board the XMM-Newtonsatellite. The spectrum exhibits bright emission lines of the H- and He- like ions of Ne, Mg, Si and S, as well as Fexviii to Fexx and Fexxv 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 NH= 710 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 Lx(0.5-10 keV)= 1:3 10 34 erg s 1 ,a ndLx(0.5-10 keV)= 0:85 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.