We present two mixing models for post-processing of 3D hydrodynamic simulations applied to convective-reactive i -process nucleosynthesis in a rapidly accreting white dwarf ( RAWD ) with \mathrm { [ Fe / H ] } = -2.6 , in which H is ingested into a convective He shell during a He flash .
A 1D advective two-stream model is formulated with physically motivated radial and horizontal mixing coefficients constrained by 3D hydrodynamic simulations .
A more traditional approach uses diffusion coefficients calculated from the same simulations .
All 3D simulations include the energy feedback of the \mathrm { { } ^ { 12 } C } ( p, \gamma ) \mathrm { { } ^ { 13 } N } reaction from the entrainment of stably stratified H. Global oscillations of shell H ingestion in two of the RAWD simulations cause bursts of entrainment of H and energy feedback into the flow .
With the same nuclear network as in the 3D simulations , the 1D advective two-stream model reproduces the rate and location of the H burning within the He shell closely matching the 3D simulation predictions , as well as qualitatively displaying the asymmetry of the X _ { \mathrm { H } } profiles between the up- and downstream .
With a full i -process network the advective mixing model captures the difference in the n-capture nucleosynthesis in the up- and downstream .
For example , \mathrm { { } ^ { 89 } Kr } and \mathrm { { } ^ { 90 } Kr } with half-lives of 3.18 \mathrm { \mathrm { min } } and 32.3 \mathrm { \mathrm { s } } differ by a factor 2 - 10 in the two streams .
In this particular application the diffusion approach provides globally the same abundance distribution as the advective two-stream mixing model .
The resulting i -process yields from the diffusive and advective post-processing models are compared with observations of the exemplary CEMP-r/s star CS31062-050 .