HIGH-RESOLUTION X-RAY SPECTROSCOPY REVEALS THE SPECIAL NATURE OF WOLF-RAYET STAR WINDS
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Oskinova-2012-HIGH-RESOLUTION X-RA.pdf
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Author(s)
Oskinova, Lidia M.
Gayley, K. G.
Hamann, W.-R.
Ignace, R.
Pollock, A. M. T.
Huenemoerder, David P.
Date Issued
February 2012
Journal
The Astrophysical Journal. Letters
Publisher
IOP Publishing
Citation
Oskinova, L. M., K. G. Gayley, W.-R. Hamann, D. P. Huenemoerder, R. Ignace, and A. M. T. Pollock. “HIGH-RESOLUTION X-RAY SPECTROSCOPY REVEALS THE SPECIAL NATURE OF WOLF-RAYET STAR WINDS.” The Astrophysical Journal 747, no. 2 (February 21, 2012): L25. © 2012 The American Astronomical Society
Version
Final published version
Abstract
We present the first high-resolution X-ray spectrum of a putatively single Wolf-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 ≈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.
MIT Department
MIT Kavli Institute for Astrophysics and Space Research
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DOI of Published Version
https://doi.org/10.1088/2041-8205/747/2/l25
