The Laminar Flame Speedup by ²² Ne Enrichment in White Dwarf Supernovae

Abstract

Carbon-oxygen white dwarfs contain 22 Ne formed from α-captures onto 14 N during core He burning in the progenitor star. In a white dwarf (type Ia) supernova, the 22 Ne abundance determines, in part, the neutronto-proton ratio and hence the abundance of radioactive 56 Ni that powers the lightcurve. The 22 Ne abundance also changes the burning rate and hence the laminar flame speed. We tabulate the flame speedup for different initial 12 C and 22 Ne abundances and for a range of densities. This increase in the laminar flame speed-about 30% for a 22 Ne mass fraction of 6%-affects the deflagration just after ignition near the center of the white dwarf, where the laminar speed of the flame dominates over the buoyant rise, and in regions of lower density ∼ 10 7 g cm −3 where a transition to distributed burning is conjectured to occur. The increase in flame speed will decrease the density of any transition to distributed burning.

Evaluating Systematic Dependencies of Type Ia Supernovae: The Influence of Deflagration to Detonation Density

“…We extrapolate a dependence of DDT density on 22 Ne content from [6] and construct a function describing the 56 Ni yield that depends on DDT density and metallicity (through the 22 Ne). We evaluate this function for the fiducial DDT density 6.76 × 10 6 g cm −3 in Figure 4.…”

“…The scheme takes as input a tabulated flame speed [6] and compensates for buoyancy effects of [9]. Carbon simmering neutronizes the core and expands the convection zone pulling in 12 C from the outer layer [10,11].…”

STUDY OF THE DETONATION PHASE IN THE GRAVITATIONALLY CONFINED DETONATION MODEL OF TYPE Ia SUPERNOVAE

“…Further investigation, including studies of three-dimensional deflagration morphologies, is needed to characterize these relationships. The details of flame propagation, including the flame speed dependence on progenitor metallicity (Chamulak et al 2007) and through the algorithm used to treat buoyancydriven turbulent nuclear burning, will also affect this mapping between flame ignition conditions and the outcome following deflagration, and should be examined in future work.…”

Simplified Hydrostatic Carbon Burning in White Dwarf Interiors

“…As first noticed by Chamulak et al (2007), neutron captures onto 56 Fe will be negligible, since the 56 Fe(n, γ ) 57 Fe reaction has a cross section approximately 64 times bigger than that of neutron capture onto 12 C, but the mole fraction of 56 Fe is approximately 1250 times smaller than that of 12 C at solar metallicity in the 12 C-rich environment of a WD. Thus, a 56 Fe abundance of more than 20 times the solar abundance would be required to compete with the reaction 12 C(n, γ ) 13 C.…”