X-Ray Emission from the Wolf-Rayet Bubble S 308

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 (T ₁ ~ 1.1 × 10⁶ K, T ₂ ~ 13 × 10⁶ K), with a total X-ray luminosity ~2 × 10³³ erg s^-1 at the assumed distance of 1.5 kpc.

Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.