Semiconvection: numerical simulations (F. Zaussinger and H. C. Spruit)

Vol. 554
In section 2. Astrophysical processes

Semiconvection: numerical simulations

by F. Zaussinger and H. Spruit A&A 554, A119

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The processes that mix stellar interiors are central to their evolution, especially during advanced stages. While classical turbulent convective transport is reasonably under control, with a number of approximations available for homogeneous interiors, the process of chemical transport not understood as well. In semiconvection, the process is governed by molecular weight gradients that develop during advanced stages of nuclear burning. Different than the now popular thermohaline ("salt finger") modes of double diffusive instability, semiconvection is less well understood. This paper presents a direct numerical simulation of single and multiple layers with density stratification. The authors show that the layers are thin and that the Boussinesq approximation yields reliable results in two dimensions that correspond to those obtained from fully compressible computations. While opacity feedback on the radiative properties of the mixing medium have not yet been included, these calculations show that such models are now feasible. The resulting mixing is minor, but thin density stratification barriers, which may be almost a full scale height in extension, produce din models of intermediate-mass stars. This will be important for dynamo, asteroseimological, and rotational studies of evolved stars, and it points the way to a fully generalized theory of inhomogeneous convection.