  Two dimensional hydrodynamical simulations of convective oxygen burning shell
in the presupernova evolution of a 20 solar-mass star are extended to later
times. We used the VULCAN code to simulate longer evolution times than
previously possible. Our results confirm the previous work of Bazan and Arnett
(98) over their time span of 400s. However, at 1200s, we could identify a new
steady state that is significantly different than the original one dimensional
model. There is considerable overshooting at both the top and bottom boundaries
of convection zone. Beyond the boundaries, the convective velocity falls off
exponentially, with excitation of internal modes. The resulting mixing greatly
affect the evolution of the simulations. Connections with other works of
simulation of convection, in which such behavior is found in a different
context, are discussed.

Astrophysics