S 308: A Textbook Example of Wolf-Rayet Bubbles
Abstract
Wolf-Rayet (WR) stars are evolved massive stars whose H-rich envelopes have been stripped by copious stellar winds at a red supergiant (RSG) or luminous blue variable (LBV) phase. The fast WR wind can sweep up the circumstellar material and form a bubble. Hydrodynamical models of WR bubbles have been calculated both analytically and numerically by García-Segura, Mac Low, and Langer.
S 308 is a circumstellar bubble blown by the WN4 star HD 50896. It is one of the only two WR bubbles that have been detected in X-rays. XMM-Newton observations of the northwestern quadrant of S 308 show X-ray emission in the bubble interior, but an apparent gap exists between the outer edge of the X-ray emission and the outer rim of the [O iii] λ 5007 emission. We have obtained high-dispersion, long-slit echelle spectra of S 308 in the Hα , [N ii] λ 6583, and [O iii] λ 5007 lines. The echelle spectra reveal a thick shell of expanding RSG wind with an outer shock advancing into the ambient interstellar medium and an inner rim of swept-up RSG wind. We have also obtained additional XMM-Newton observations to map the entire bubble of S 308. The X-ray mosaic image of S 308 shows that the hot gas is confined within the innermost swept-up RSG wind shell. These results indicate that S 308 is a textbook example of WR bubbles modeled by García-Segura et al. Our upcoming FUSE observations of O vi line emission from S 308 will further allow us to investigate the thermal conduction between the cold nebular shell and the hot interior gas.- Publication:
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American Astronomical Society Meeting Abstracts
- Pub Date:
- December 2004
- Bibcode:
- 2004AAS...20513801C