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Y.-H. Chu, R.A. Gruendl (UIUC), M.A. Guerrero (IAA/CSIC), G. Garcia-Segura (UNAM), S.L. Snowden (USRA/GSFC)
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 Garc\'{i}a-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~{\sc iii}] \lambda5007 emission.
We have obtained high-dispersion, long-slit echelle spectra of S\,308 in the H\alpha, [N~{\sc ii}] \lambda6583, and [O~{\sc iii}] \lambda5007 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 Garc\'{i}a-Segura et al. Our upcoming FUSE observations of O~{\sc 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.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.