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Session 19 - Hot Stars.
Display session, Monday, January 15
North Banquet Hall, Convention Center

[19.07] Hydrodynamical Simulations of Core Silicon Burning

G. Bazan, D. Arnett (Steward Obs.)

We use an application of the piecewise parabolic method (PPM) of numerical hydrodynamics on massively parallel computers to study core silicon burning in massive stars. Core silicon burning lays the foundation for Type Ib/Ic/II SNe in that the Fe core mass, electron fraction, and entropy are determined at that time. Each of these quantities has already been found to play an important role during core collapse, shock propagation, and neutrino emission. In core silicon burning, simulations must contend with convection and its interaction with nuclear burning and neutrino cooling, something which mixing length theory cannot provide in a self-consistent manner. In effect, this stage of evolution is very similar to shell silicon and oxygen burning, which we have already simulated in two dimensions (Bazan and Arnett 1994, 1995a,b), in that convection depends on the competition between nuclear heating and neutrino cooling, rather than the normal cooling by radiative diffusion. However, since silicon burning actually results in a nuclear statistical equilibrium (NSE) composition, the exact treatment of weak interaction processes, including contributions from enhanced electron captures and beta-decays due to the Fermi energy being greater than the thermal energy, must also be included. First, comparisons will be made against one-dimensional, quasi-static models. Next, we compare three different approaches of handling weak interactions: a schematic NSE distribution based on previous work (Arnett 1977; Bethe, Brown, Applegate and Lattimer 1979), (2) a 90 isotope network from e^- to Zn using recently published equilibrium URCA rates (Arnett 1995), and (3) a 90 isotope network from e^- to Zn using non-equilibrium rates incorporating enhanced forward and backward channels due to high lying Gamow-Teller and Fermi resonances. We also will comment on the nature of this study as a benchmark for future massively parallel computing platforms.

Arnett, W. D. 1977, Ap. J., 218, 815. Arnett, W. D. 1995, in "Supernovae: A History of Matter from the Big Bang to the Present", (). Bazan, G. amp; Arnett, D. 1994, Ap. J., 433, L41. Bazan, G. amp; Arnett, D. 1995a, in preparation. Bazan, G. amp; Arnett, D. 1995b, in preparation. Bethe, H., Brown, G., Applegate, J., and Lattimer, J. 1979, Nucl. Phys., A324, 487.

Program listing for Monday