More Einstein Views of Wolf-Rayet Stars

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 eflection rating pectrometers () and the uropean hoton maging ameras (- and )  spectrometers on board the XMM-Newton satellite. The spectrum exhibits bright emission lines of the H-and Helike ions of Ne, Mg, Si and S, as well as Fe  to Fe  and Fe  lines. Line fluxes have been measured. The  and  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 H = 7×10 21 cm −2 . Multi-temperature () 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 x (0.5-10 keV) = 1.3 × 10 34 erg s −1 , and L x (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  emission-line complex at ∼ 6.7 keV is argued as being indicative for colliding winds inside a WR+O binary system.

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XMM-Newton observations of the nitrogen-rich Wolf-Rayet star WR 1

Ignace

Oskinova²,

Brown

2003

A&A

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Abstract. We present XMM-Newton results for the X-ray spectrum from the N-rich Wolf-Rayet (WR) star WR 1. The EPIC instrument was used to obtain a medium-resolution spectrum. The following features characterize this spectrum: (a) significant emission "bumps" appear that are coincident with the wavelengths of typical strong lines, such as Mg, Si, and S; (b) little emission is detected above 4 keV, in contrast to recent reports of a hard component in the stars WR 6 and WR 110 which are of similar subtype; and (c) evidence for sulfur K-edge absorption at about 2.6 keV, which could only arise from absorption of X-rays by the ambient stellar wind. The lack of hard emission in our dataset is suggestive that WR 1 may truly be a single star, thus representing the first detailed X-ray spectrum that isolates the WR wind alone (in contrast to colliding wind zones). Although the properties of the S-edge are not well-constrained by our data, it does appear to be real, and its detection indicates that at least some of the hot gas in WR 1 must reside interior to the radius of optical depth unity for the total absorptive opacity at the energy of the edge.

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More Einstein Views of Wolf-Rayet Stars

Cited by 4 publications

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Wolf-Rayet stars

Wolf-Rayet stars

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

XMM-Newton observations of the nitrogen-rich Wolf-Rayet star WR 1

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