TY  - JOUR
A1  - Oskinova, Lida
A1  - Gayley, K. G.
A1  - Hamann, Wolf-Rainer
A1  - Huenemoerder, D. P.
A1  - Ignace, R.
A1  - Pollock, A. M. T.
T1  - HIGH-RESOLUTION X-RAY SPECTROSCOPY REVEALS THE SPECIAL NATURE OF
 WOLF-RAYET STAR WINDS
JF  - ASTROPHYSICAL JOURNAL LETTERS
N2  - We present the first high-resolutionX-ray spectrum of a putatively singleWolf-Rayet (WR) star. 400 ks observations of WR 6 by the XMM-Newton telescope resulted in a superb quality high-resolution X-ray spectrum. Spectral analysis reveals that the X-rays originate far out in the stellar wind, more than 30 stellar radii from the photosphere, and thus outside the wind acceleration zone where the line-driving instability (LDI) could create shocks. The X-ray emitting plasma reaches temperatures up to 50 MK and is embedded within the unshocked, "cool" stellar wind as revealed by characteristic spectral signatures. We detect a fluorescent Fe line at approximate to 6.4 keV. The presence of fluorescence is consistent with a two-component medium, where the cool wind is permeated with the hot X-ray emitting plasma. The wind must have a very porous structure to allow the observed amount of X-rays to escape. We find that neither the LDI nor any alternative binary scenario can explain the data. We suggest a scenario where X-rays are produced when the fast wind rams into slow "sticky clumps" that resist acceleration. Our new data show that the X-rays in single WR star are generated by some special mechanism different from the one operating in the O-star winds.
KW  - stars: individual (WR 6)
KW  - stars: winds, outflows
KW  - stars: Wolf-Rayet
KW  - X-rays: stars
Y1  - 2012
U6  - https://doi.org/10.1088/2041-8205/747/2/L25
SN  - 2041-8205
VL  - 747
IS  - 2
PB  - IOP PUBLISHING LTD
CY  - BRISTOL
ER  -