Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...455..160g&link_type=abstract
Astrophysical Journal v.455, p.160
Astronomy and Astrophysics
Astronomy
58
Hydrodynamics, Ism: Bubbles, Stars: Mass Loss, Stars: Wolf-Rayet
Scientific paper
We perform two-dimensional gasdynamical simulations to model the growth 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 we have proposed in Garcia-Segura & Mac Low (1995, 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 main-sequence bubble either cools or remains hot and pressurized. We simulate the history of a realistic bubble using qualitative simulations. We then perform a numerical resolution study to get a quantitative description of the swept-up, unstable shell.
We find that the Vishniac instability dominates the behavior of the ring nebula, while the W-R wind sweeps up the red supergiant wind. Clumps form with column densities 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 magnitude. As a result, external neutral shells probably cannot exist around W-R ring nebulae. The only place neutral material could exist would be within dense, self-shielding clumps. When the W-R wind finishes sweeping 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° wavelength to be dominant in the clumpy shell. The shapes and dynamics of the individual blowouts suggest that observed W-R ring nebulae such as NGC 6888 lie within main-sequence 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% slower than the interclump shell and contain less than 65% of the shell kinetic energy expected from analytic models. At this time, the observable clumps carry less than 18% of the total wind kinetic energy.
Garcia-Segura Guillermo
Mac Low Mordecai-Mark
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