Hot gas in the circumstellar bubble S308

You Hua Chu, Martín A. Guerrero, Robert A. Gruendl, Guillermo García-Segura, Heinrich J. Wendker

Research output: Contribution to journalArticlepeer-review


S308 is a circumstellar bubble blown by the WN4 star HD 50896. It is one of the only two single-star bubbles that show detectable diffuse X-ray emission. We have obtained XMM-Newton EPIC observations of the northwest quadrant of S308. The diffuse X-ray emission shows a limb-brightened morphology, with a clear gap extending from the outer edge of the diffuse X-ray emission to the outer rim of the nebular shell. The X-ray spectrum of the diffuse emission is very soft and is well fitted by an optically thin plasma model for an N-enriched plasma at temperatures of ∼1.1 × 106 K. A hotter gas component may exist but its temperature is not well constrained since it contributes less than 6% of the observed X-ray flux. The total X-ray luminosity of S308, extrapolated from the bright northwest quadrant, is ≤(1. 2 ± 0.5) × 1034 ergs s-1. We have used the observed bubble dynamics and the physical parameters of the hot interior gas of S308, in conjunction with the circumstellar bubble model of García-Segura & Mac Low, to demonstrate that the X-ray-emitting gas must be dominated by mixed-in nebular material.

Original languageEnglish (US)
Pages (from-to)1189-1195
Number of pages7
JournalAstrophysical Journal
Issue number2 I
StatePublished - Dec 20 2003


  • ISM: bubbles
  • ISM: individual (S308)
  • Stars: Wolf-Rayet
  • Stars: individual (HD 50896)
  • Stars: winds, outflows
  • X-rays: individual (S308)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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