TURBULENT CHEMICAL DIFFUSION IN CONVECTIVELY BOUNDED CARBON FLAMES
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Lecoanet-2016-TURBULENT CHEMICAL DIFFUSION IN.pdf
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Author(s)
Lecoanet, Daniel
Schwab, Josiah
Quataert, Eliot
Bildsten, Lars
Timmes, F. X.
Vasil, Geoffrey M.
Oishi, Jeffrey S.
Brown, Benjamin P.
Burns, Keaton James
Date Issued
November 2016
Journal
Astrophysical Journal
Publisher
IOP Publishing
Citation
Lecoanet, Daniel et al. “TURBULENT CHEMICAL DIFFUSION IN CONVECTIVELY BOUNDED CARBON FLAMES.” The Astrophysical Journal 832.1 (2016): 71. © 2016 The American Astronomical Society
Version
Final published version
Abstract
It has been proposed that mixing induced by convective overshoot can disrupt the inward propagation of carbon deflagrations in super-asymptotic giant branch stars. To test this theory, we study an idealized model of convectively bounded carbon flames with 3D hydrodynamic simulations of the Boussinesq equations using the pseudo-spectral code Dedalus. Because the flame propagation timescale is much longer than the convection timescale, we approximate the flame as fixed in space, and only consider its effects on the buoyancy of the fluid. By evolving a passive scalar field, we derive a turbulent chemical diffusivity produced by the convection as a function of height, D[subscript t][subscript z]). Convection can stall a flame if the chemical mixing timescale, set by the turbulent chemical diffusivity, D[subscript t], is shorter than the flame propagation timescale, set by the thermal diffusivity, κ, i.e., when D[subscript t] < kappa. However, we find D[subscript t] < kappa for most of the flame because convective plumes are not dense enough to penetrate into the flame. Extrapolating to realistic stellar conditions, this implies that convective mixing cannot stall a carbon flame and that "hybrid carbon–oxygen–neon" white dwarfs are not a typical product of stellar evolution.
MIT Department
Massachusetts Institute of Technology. Department of Physics
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DOI of Published Version
https://doi.org/10.3847/0004-637x/832/1/71
