Astronomy and Astrophysics – Astronomy
Scientific paper
May 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003aas...202.3216g&link_type=abstract
American Astronomical Society Meeting 202, #32.16; Bulletin of the American Astronomical Society, Vol. 35, p.746
Astronomy and Astrophysics
Astronomy
3
Scientific paper
NGC 6888, the Crescent Nebula, is a circumstellar bubble blown by the fast wind of the Wolf-Rayet star HD 192163. Diffuse X-ray emission from its interior has been previously detected by Einstein, ROSAT, and ASCA with 30''--150'' angular resolution. We have obtained a Chandra ACIS-S observation of the northeast quadrant of NGC 6888 with 1'' resolution. The observation clearly resolved point sources from the diffuse X-ray emission. A total of 13,000 counts from the diffuse emission were detected. The diffuse X-ray emission shows a limb-brightened morphology with spatial extent similar to that of the cool, dense nebular shell, but with the X-ray emission peaking interior to the optical emission. The integrated X-ray spectrum is soft, showing prominent N vii lines consistent with the N-enriched nebular abundance. Spectral fits with a thin plasma model indicate that the hot gas in NGC 6888 has a temperature of T ˜ 2.8*E6 K (kT ˜ 0.24 keV). This temperature is higher than that of S 308, but similar to those found in planetary nebulae. The differences in morphology and plasma temperature between NGC 6888 and S 308 suggest an evolutionary effect consistent with their dynamic ages, 24,000 yr for NGC 6888 and 70,000 yr for S 308.
Chu Y.-H. Y.-H.
Gruendl Robert A.
Guerrero Martin A.
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