J. A. Toalá, M. A. Guerrero, Y. -H. Chu, R. A. Gruendl, S. J. Arthur, R. C. Smith, S. L. Snowden
The Wolf-Rayet (WR) bubble S\,308 around the WR star HD\,50896 is one of the
only two WR bubbles known to possess X-ray emission. We present
\textit{XMM-Newton} observations of three fields of this WR bubble that, in
conjunction with an existing observation of its Northwest quadrant, map most of
the nebula. The X-ray emission from S\,308 displays a limb-brightened
morphology, with a 22\arcmin\ in size central cavity and a shell thickness of
$\sim$8\arcmin. This X-ray shell is confined by the optical shell of ionized
material. The spectrum is dominated by the He-like triplets of \ion{N}{6} at
$\sim$0.43 keV and \ion{O}{7} at $\sim$0.5 keV, and declines towards high
energies, with a faint tail up to 1 keV. This spectrum can be described by a
two-temperature optically thin plasma emission model ($T_1\sim1.1\times10^6$ K,
$T_2\sim13\times10^6$ K), with a total X-ray luminosity $\sim3\times10^{33}$
erg s$^{-1}$ at the assumed distance of 1.8 kpc. Qualitative comparison of the
X-ray morphology of S\,308 with the results of numerical simulations of
wind-blown WR bubbles suggests a progenitor mass of $40\,M_\odot$ and an age in
the WR phase $\sim$20,000 yrs. The X-ray luminosity
View original:
http://arxiv.org/abs/1201.2879
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