WOLF-RAYET BUBBLES .2. GASDYNAMICAL SIMULATIONS

We perform two-dimensional gasdynamical simulations to model the growt h of a stellar wind bubble around a Wolf-Rayet (W-R) star, taking into account the prior main-sequence and red supergiant phases. Following the three-wind model eve have proposed in Garcia-Segura & Mac Low (199 5, Paper I), we take the main-sequence, red supergiant, and W-R winds each to be constant in time. We consider the possibilities that the ma in-sequence bubble either cools or remains hot and pressurized. We sim ulate the history of a realistic bubble using qualitative simulations. We then perform a numerical resolution study to get a quantitative de scription of the swept-up, unstable shell. We find that the Vishniac i nstability dominates the behavior of the ring nebula, while the W-R wi nd sweeps up the red supergiant wind. Clumps form with column densitie s at least a factor of 2 higher than the unperturbed shell, while the column density in the rest of the shell decreases by two orders of mag nitude. As a result, external neutral shells probably cannot exist aro und W-R ring nebulae. The only place neutral material could exist woul d be within dense, self-shielding clumps. When the W-R wind finishes s weeping up the red supergiant wind, it breaks out into the surrounding low-density, main-sequence bubble, becoming Rayleigh-Taylor unstable. At breakout, we find a 12 degrees wavelength to be dominant in the cl umpy shell. The shapes and dynamics of the individual blowouts suggest that observed W-R ring nebulae such as NGC 6888 lie within main-seque nce bubbles that have already cooled. No more than 90% of the swept-up gas lies in visible clumps. Before blowout, clumps travel up to 40% s lower than the interclump shell and contain less than 65% of the shell kinetic energy expected from analytic models. At this time, the obser vable clumps carry less than 18% of the total wind kinetic energy.