TL;DR
This paper presents numerical simulations of semiconvection in astrophysical conditions, exploring layered double-diffusive convection, validating approximations, and providing formulas for superadiabatic gradients relevant to stellar models.
Contribution
It offers a translation between astrophysical fluid mechanics and Boussinesq approximation, validates this approach, and provides a fitting formula for superadiabatic gradients in semiconvection.
Findings
Layered convection occurs in astrophysical semiconvection.
The Boussinesq approximation is valid for thin layers.
Superadiabatic gradient depends on layer thickness.
Abstract
A grid of numerical simulations of double-diffusive convection is presented for astrophysical conditions. As in laboratory and geophysical cases convection takes place in a layered form. A translation between the astrophysical fluid mechanics and incompressible (Boussinesq) approximation is given, valid for thin layers. Its validity is checked by comparison of the results of fully compressible and Boussinesq simulations of semiconvection. A fitting formula is given for the superadiabatic gradient as a function of this parameter. The superadiabaticity depends on the thickness of the double diffusive layers, for which no good theory is available, but the effective He-diffusion coefficient is nearly independent of . For a fiducial main sequence model (15 ) the inferred mixing time scale is of the order yr.
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Taxonomy
TopicsGeophysics and Gravity Measurements · Geomagnetism and Paleomagnetism Studies · Solar and Space Plasma Dynamics