Hydrodynamical Simulations of Convective Burning Shells \\ In Massive Stars

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Session 111 -- Stellar Interiors
Display presentation, Saturday, January 15, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[111.04] Hydrodynamical Simulations of Convective Burning Shells \\ In Massive Stars

Grant Bazan (Steward Observatory), David Arnett (Steward Observatory)

The nature of convective O and Si burning shells in the last phases of massive star evolution affects both the nucleosynthesis of intermediate and Fe-peak nuclei and many of quantities relevant to the subsequent supernova. Part of our understanding of the solar isotopic distribution in the region from Si to Ni is derived from our knowledge of this stellar evolutionary stage. In addition, the amount of $^{56}$Ni, necessary to power all supernovae light curves, is critically dependent on what transpires in this stage. Normally, common mixing length theory (MLT) is employed in quasistatic stellar evolution codes to describe both the energy and particle transport in these regions. Two assumptions usually arise regarding particle transport from MLT : (1) convection is efficient enough to simply smooth out any composition perturbations caused by nuclear processing, (2) composition concentrations arising from nucleosynthesis diffuse throughout the convective region according to the average eddy speed prescribed by MLT. In most cases in stellar evolution involving convection, either of these approaches is adequate to describe composition evolution and the resulting energy generation and flow. However, when both nuclear evolution timescales are less than the mixing timescale implied from MLT and expected density perturbations caused by the convection reach the linearity limit, neither of these approaches can be considered accurate to describe the energy and particle transport in these regions. We combine the detailed microphysics commonly found in quasistatic stellar evolution codes with the PPM hydrodynamics code PROMETHEUS in order to study the nucleosynthesis and hydrodynamics of convective O- and Si- burning shells. Isotopes whose nucleosynthesis is most likely to deviate from a MLT scenario are identified. We compare the resulting compositions with those of assumed efficient mixing and diffusive mixing scenarios

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