* Astronomy

Title: X-ray emission from the Wolf-Rayet bubble S308
Authors: 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 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' in size central cavity and a shell thickness of ~8'. This X-ray shell is confined by the optical shell of ionised material. The spectrum is dominated by the He-like triplets of N{6} at ~0.43 keV and O{7} at ~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 ~1.1 x 10^6 K, T_2 ~13 x 10^6 K), with a total X-ray luminosity ~3 x 10^{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 solar masses and an age in the WR phase ~20,000 yrs.

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