S-process in hot AGB stars: A complex interplay between diffusive mixing and nuclear burning

We present new qualitative results of the s-process nucleosynthesis in hot AGB stars resulting from diffusive convective overshooting. In this approach, protons from the convective envelope are injected into the adjacent C-12-rich layers, but depending on the thermodynamic conditions in the mixing zone, the nuclear proton lifetime can be comparable with (or even smaller than) the diffusion timescale. In such a case, the nucleosynthesis and diffusion equations must be coupled. Our simulations indicate that during this diffusive burning phase, the N-14-rich and C-13-rich layers overlap with drastic impact on the s-process distribution. Our study emphasizes the sensitivity of the s-process nucleosynthesis on the temperature of the partial mixing zone. We show that in this framework, a deep hot third dredge-up tends to inhibit the production of s-elements. We also provide a first qualitative estimate of the metallicity and mass dependence of the s-process efficiency in AGB stars and propose that this complex interplay could account for the large variety of the observed s-process efficiencies.