A Reexamination of the Core Helium Flash

The possibility of a dynamical core helium Ñash has been studied with two-dimensional hydrodynamic simulations using three separate turbulence models for the treatment of time-dependent convection. Two of these are simple algebraic eddy viscosity models. The third model involves a separate equation for the turbulent kinetic energy density, which then feeds into an expression for the eddy viscosity. One of the simple eddy viscosity models is that used by Cole & Deupree in studies of the core helium Ñash about Ðfteen years ago. I Ðnd that this model can be made to produce a more quiescent Ñash than Cole & Deupree found by substantially reducing the eddy viscosity from their value. When this is done, all three turbulence models produce the same primary resultÈthe Ñash does not produce a hydrodynamic event. However, the traditional assumption of adiabatic convection through the Ñash evolution is found in all cases to be inadequate, primarily through the extensive heating of the region interior to the convective region. Subject headings : convection È hydrodynamics È stars : interiors