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Depending on mass and metallicity as well as evolutionary phase, starsoccasionally experience convective-reactive nucleosynthesis episodes. Wespecifically investigate the situation when nucleosynthetically unprocessed,H-rich material is convectively mixed with a He-burning zone, for example inconvectively unstable shell on top of electron-degenerate cores in AGB stars,young white dwarfs or X-ray bursting neutron stars. Such episodes arefrequently encountered in stellar evolution models of stars of extremely low orzero metal content [...] We focus on the convective-reactive episode in thevery-late thermal pulse star Sakurai's object (V4334 Sagittarii). Asplund etal.(1999) determined the abundances of 28 elements, many of which are highlynon-solar, ranging from H, He and Li all the way to Ba and La, plus the Cisotopic ratio. Our simulations show that the mixing evolution according tostandard, one-dimensional stellar evolution models implies neutron densities inthe He that are too low to obtain a significant neutron capture nucleosynthesison the heavy elements. We have carried out 3D hydrodynamic He-shell flashconvection [...] we assume that the ingestion process of H into the He-shellconvection zone leads only after some delay time to a sufficient entropybarrier that splits the convection zone [...] we obtain significantly higherneutron densities (~few 10^15 1/cm^3) and reproduce the key observed abundancetrends found in Sakurai's object. These include an overproduction of Rb, Sr andY by about 2 orders of magnitude higher than the overproduction of Ba and La.Such a peculiar nucleosynthesis signature is impossible to obtain with themixing predictions in our one-dimensional stellar evolution models. [...] Wedetermine how our results depend on uncertainties of nuclear reaction rates,for example for the C13(\alpha, n)O16 reaction.

astrophysical journal/the astrophysical journal

Convective-reactive proton-C12 combustion in Sakurai's object (V4334  Sagittarii) and implications for the evolution and yields from the first  generations of stars