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Session 27 - Variable Stars, Novae, & Supernovae.
Display session, Tuesday, June 10
South Main Hall,
It has been theorized for some time now that the progenitor of the supernova remnant Cassiopeia A was surrounded by a dense shell of circumstellar material. This shell is believed to have formed as a result of the interaction of a slow stellar wind, ejected while the star was a red giant, and a fast wind, ejected when the star became a blue giant. Current theory claims that the fast blue wind shocked the slow red wind into a spherical shell of approximately constant thickness and density. The ragged appearance of the supernova remnant can be partially explained by the instabilities arising from the interaction of the supernova blast wave with this spherical shell. There is, however, an asphericity to the remnant which suggests the shell was not spherical.
If the red giant wind had been more dense around the equator of the star than at the poles, an elliptical shell could have resulted. To explore this scenario, the VH-1 code was modified to simulate a pre-Sedov mass-driven wave shocking an elliptical shell of constant density and of thickness a function of angle. Initial results yield instabilities similar to those of the spherical model. However, the pattern for the elliptical shell changes as a function of angle and may therefore lead to a model which fits Cas A as presently observed. Future modifications of this model include shifting the center of the shell with respect to the blast wave and roughening of the simulation grid to remove artificially smooth interactions.
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Program listing for Tuesday