Tuesday, July 16, 2013

1307.3821 (Paul R. Woodward et al.)

Hydrodynamic Simulations with PPMstar. Methods and Convergence Study of Entrainment at the Top Boundary of Shell Convection in Stellar Interiors    [PDF]

Paul R. Woodward, Falk Herwig, Pei-Hung Lin
He-shell flash convection in AGB stars of very low metallicity, in post-AGB or pre-white dwarf stars or in accreting white dwarfs may under certain conditions grow and extend into the H-rich layers above. In this case proton-rich material will be advected into the deep C12-rich He-burning layers leading to a regime of H-C12 combustion which may lead to an observable (e.g. Sakurai's object) stellar response in real-time. This is the nucleosynthesis site of the i process. The properties of this violent phase of stellar evolution depend on the interplay of fuel advection, mixing and nuclear energy production associated with dynamic feedback into the fluid flow. We present 3-dimensional, fully compressible gas-dynamics simulations in 4pi geometry of He-shell flash convection with proton-rich fuel entrainment at the upper boundary. We are focusing on the properties of entrainment of material, and establish the quantitative dependence of the entrainment rate on grid resolution. We find that, with our numerical technique, simulations with 1024^3 cells or more are required to reach a numerical fidelity appropriate for the problem. However, only the results from the 1536^3 simulation provides evidence that we do reach convergence with regard to the entrainment rate. Our results demonstrate that our method, which is described in detail, can provide quantitative results related to entrainment and convective boundary mixing in deep stellar interior environments, which opens up an array of new applications.
View original: http://arxiv.org/abs/1307.3821

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