Large nuclear networks in presupernova models

We outline the role of multidimensional hydrodynamics coupled to large nuclear networks in the case of core silicon burning in massive stars. Using an implementation of the Piecewise Parabolic Method (PPM) of solving the Euler equations for mass, momentum, and total energy, we examine the differences and similarities between a 1-D hydrostatic stellar evolution model and a 2-D hydrodynamical model at two resolutions. We find that 2-D models exhibit significantly less vigorous convection than 1-D hydrostatic models, and that the core compensates for the lack of energy production by increasing temperatures and densities through contraction. Equilibration between the Si-burning and convective timescales appears to occur. Including an 123 isotope network from Y_e to ⁵⁶Ge to the hydrodynamic code leads to similar global behaviors as the 2-D model with the simplified burning algorithm used in the 1-D models. However, significant inhomogeneity in iron peak isotope composition occurs, which could have important consequences to energy losses via electron captures onto G-T resonances and the local energetics which drive convective silicon burning.