Hot Gas in Wolf-Rayet Bubbles. I. XMM-Newton Observations of S 308

Details Hot Gas in Wolf-Rayet Bubbles. I. XMM-Newton Observations of S 308 Hot Gas in Wolf-Rayet Bubbles. I. XMM-Newton Observations of S 308

May 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003aas...202.3215c&link_type=abstract

American Astronomical Society Meeting 202, #32.15; Bulletin of the American Astronomical Society, Vol. 35, p.745

Astronomy and Astrophysics

Astronomy

Scientific paper

S 308 is a circumstellar bubble blown by the fast wind of the Wolf-Rayet star HD 50896. Diffuse X-ray emission from its interior has been previously detected by ROSAT; however, a significant fraction of the diffuse emission was occulted by the PSPC window support structure, making it difficult to determine the distribution of X-ray emission. Spectral analysis is also difficult because of its low surface brigthness and contamination by point sources. We have obtained XMM-Newton observations of the northewest quadrant of S 308 with 10'' resolution. The exposure time was 47 ks, but a high-background flare occurred during the observation and limited the useful exposure times to 22.7 ks and 16.9 ks for the EPIC/MOS and EPIC/pn observations, respectively. Even with reduced exposures, diffuse X-ray emission from S 308 was clearly detected. The X-ray emission shows a limb-brightened morphology; however, a distinct gap with widths of 100--200'' (0.7--1.4 pc) exists between the optical shell rim and the outer edge of the diffuse X-ray emission. This is in sharp contrast to NGC 6888, in which the X-ray emission extends all the way to the edge of the optical shell. The integrated X-ray spectrum of S 308 is soft, showing prominent N vii lines which reflect the enhanced N abundance in the nebula. Spectral fits with thin plasma model indicate that the hot gas in S 308 has a temperature of T ˜ 1.1*E6 K (kT ˜ 0.094 keV). This temperature is lower than those of NGC 6888 and planetary nebulae, 2--3x106 K. The differences in morphology and plasma temperature between S 308 and NGC 6888 may be attributed to an evolutionary effect, as S 308 is 70,000 yr old and NGC 6888 is only 24,000 yr old.

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