Vol. 533
In section 7. Stellar structure and evolution

Multidimensional hydrodynamic simulations of the hydrogen injection flash

by M.Mocak, L.Siess, and E.Muller, A&A 533, A53


The study presents 2D and 3D nuclear-hydrodynamic models (using HERAKLES, derived from PROMETHEUS) and a stellar evolution code to model the time and full space development of convection during shell burning in the presence of convection during the core helium flash. The aim is to study the penetration of convection induced during the ignition stages and to test how the mixing proceeds. The study shows that the hydrogen zone is indeed penetrated and that mixing can be far more efficient than previously found. The models apply to Pop. I stars that have been previously modeled with a mean field estimate of entrainment by convective plumes. This study extends the treatment to a full CNO network in 3D and can be used to calibrate the approximations required in 1D evolutionary calculations. Strong penetrative mixing is found at the lower shell boundary, regardless of the entropy differences, because the convection is organized into large eddy-like flows and strongly concentrated filaments.