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标题：X-RAY EMISSION FROM THE WOLF-RAYET BUBBLE NGC 6888. I. CHANDRA ACIS-S OBSERVATIONS
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作者：J. A. Toalá ; M. A. Guerrero ; R. A. Gruendl 等
期刊名称：The Astronomical journal
印刷版ISSN：0004-6256
电子版ISSN：1538-3881
出版年度：2014
卷号：147
期号：2
DOI：10.1088/0004-6256/147/2/30
语种：English
出版社：American Institute of Physics
摘要：We analyze Chandra observations of the Wolf-Rayet (W-R) bubble NGC 6888. This W-R bubble presents similar spectral and morphological X-ray characteristics to those of S 308, the only other W-R bubble also showing X-ray emission. The observed spectrum is soft, peaking at the N VII line emission at 0.5 keV, with additional line emission at 0.7-0.9 keV and a weak tail of harder emission up to ~1.5 keV. This spectrum can be described by a two-temperature optically thin plasma emission model (T 1 ~ 1.4 × 106 K, T 2 ~ 7.4 × 106 K). We confirm the results of previous X-ray observations that no noticeable temperature variations are detected in the nebula. The X-ray-emitting plasma is distributed in three apparent morphological components: two caps along the tips of the major axis and an extra contribution toward the northwest blowout not reported in previous analyses of the X-ray emission toward this W-R nebula. Using the plasma model fits of the Chandra ACIS spectra for the physical properties of the hot gas and the ROSAT PSPC image to account for the incomplete coverage of Chandra observations, we estimate a luminosity of L X = (7.7 ± 0.1) ×1033 erg s–1 for NGC 6888 at a distance of 1.26 kpc. The average rms electron density of the X-ray-emitting gas is 0.4 cm–3 for a total mass 1.2 M ☉.
关键词：ISM: bubbles;ISM: individual objects (NGC 6888);stars: winds; outflows;stars: Wolf–Rayet;X-rays: individual (NGC 6888) Online-only material: color figures 6 6