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 [Fe/H] =-2.6, in which H is ingested into a convective He shell. A 1D advective two-stream model adopts physically motivated radial and horizontal mixing coefficients constrained by 3D hydrodynamic simulations. A simpler approach uses diffusion coefficients calculated from the same simulations. All 3D simulations include the energy feedback of the 12C(p, γ)13N reaction from the H entrainment. Global oscillations of shell H ingestion in two of the RAWD simulations cause bursts of entrainment of H and non-radial hydrodynamic feedback. 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 XH profiles between the upstream and downstream. With a full i-process network the advective mixing model captures the difference in the n-capture nucleosynthesis in the upstream and downstream. For example, 89Kr and 90Kr with half-lives of 3.18 min and 32.3 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 are in excellent agreement with observations of the exemplary CEMP-r/s star CS31062-050.
Bibliographical noteFunding Information:
FH acknowledges funding from NSERC through a Discovery Grant. This research is supported by the National Science Foundation (USA) under Grant No. PHY-1430152 (JINA Center for the Evolution of the Elements). RA, who completed part of this work as a CITA National Fellow, acknowledges support from the Canadian Institute for Theoretical Astrophysics and from the Klaus Tschira Stiftung. PRW acknowledges NSF grants 1413548 and AST-1814181.
© 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.
- nuclear reactions, nucleosynthesis, abundances
- stars: evolution
- stars: interiors
- stars: white dwarfs