TY - JOUR
T1 - TURBULENT CHEMICAL DIFFUSION in CONVECTIVELY BOUNDED CARBON FLAMES
AU - Lecoanet, Daniel
AU - Schwab, Josiah
AU - Quataert, Eliot
AU - Bildsten, Lars
AU - Timmes, F. X.
AU - Burns, Keaton J.
AU - Vasil, Geoffrey M.
AU - Oishi, Jeffrey S.
AU - Brown, Benjamin P.
N1 - Publisher Copyright:
© 2016. The American Astronomical Society. All rights reserved.
PY - 2016/11/20
Y1 - 2016/11/20
N2 - 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, Dt (z). Convection can stall a flame if the chemical mixing timescale, set by the turbulent chemical diffusivity, Dt, is shorter than the flame propagation timescale, set by the thermal diffusivity, κ, i.e., when Dt ≥ k. However, we find Dt >k 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 carbonoxygenneon white dwarfs are not a typical product of stellar evolution.
AB - 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, Dt (z). Convection can stall a flame if the chemical mixing timescale, set by the turbulent chemical diffusivity, Dt, is shorter than the flame propagation timescale, set by the thermal diffusivity, κ, i.e., when Dt ≥ k. However, we find Dt >k 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 carbonoxygenneon white dwarfs are not a typical product of stellar evolution.
KW - convection
KW - hydrodynamics
KW - stars: interiors
KW - turbulence
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U2 - 10.3847/0004-637X/832/1/71
DO - 10.3847/0004-637X/832/1/71
M3 - Article
AN - SCOPUS:84996483317
SN - 0004-637X
VL - 832
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
M1 - 71
ER -