2012ApJ...755...77T

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 central cavity ∼22' in size and a shell thickness of ∼8'. This X-ray shell is confined by the optical shell of ionized material. The spectrum is dominated by the He-like triplets of N VI at 0.43 keV and O VII at 0.57 keV, and declines toward high energies, with a faint tail up to 1 keV. This spectrum can be described by a two-temperature optically thin plasma emission model (T₁ ∼ 1.1x10⁶ K, T₂∼ 13x10⁶ K), with a total X-ray luminosity ∼2 x10³³ erg/s at the assumed distance of 1.5 kpc.