1. Evolving a self-similar driven wave with s=2 and n=8.6 to fully develop the convective instability expected behind the shockwave as it propagates through the undisturbed stellar wind of the BSG progenitor.
2. Running this evolved SSDW into a reverse wind shock at a distance roughly one-half the distance to the inner ring, and following its evolution until it reaches the ring.
3. Running this final blastwave into the HST ring.

This density image shows the fully saturated convective instability in the self-similar driven wave. Red marks the highest density gas, the shocked stellar ejecta. The yellow underneath the band of red is the unshocked (supersonic) ejecta, and the light blue is the shocked CSM.

This density image shows the blastwave after it has encountered the reverse wind shock, and just before it hits the HST ring. A blastwave that started out in a circumstellar wind has a higher density in the shocked ejecta, and longer, narrower fingers from the convective instability, than a blastwave that propagated entirely in a uniform density environment.

The following sequence shows the density of the gas at four successive times during the encounter of the blastwave with the dense ring of gas surrounding the supernova. The presence of the Rayleigh-Taylor fingers in the unstable blastwave can alter the dynamics of the impact such that the pressure at the surface of the ring rises faster than without the fingers, perhaps shifting the turn-on of the X-ray emission to earlier times.

The role of the Rayleigh-Taylor fingers in modifying the pressure at the surface of the ring is best seen in this MPEG animation of the gas pressure. Notice in this frame the high pressure behind a reflected shock reflecting off the head of a RT finger.
(MPEG is 500 kbytes)