First models of the s process in AGB stars of solar metallicity for the stellar evolutionary code ATON with a novel stable explicit numerical solver

Aims. We describe the first s-process post-processing models for asymptotic giant branch (AGB) stars of masses 3, 4, and 5 M· at solar metallicity (Z = 0.018) computed using the input from the stellar evolutionary code ATON. 

Methods. The models are computed with the new code SNUPPAT (S-process NUcleosynthesis Post-Processing code for ATON), which includes an advective scheme for the convective overshoot that leads to the formation of the main neutron source, 13C. Each model is post-processed with three different values of the free overshoot parameter. Included in the code SNUPPAT is the novel Patankar-Euler-Deflhard explicit numerical solver, which we use to solve the nuclear network system of differential equations. 

Results. The results are compared to those from other s-process nucleosynthesis codes (Monash, FRUITY, and NuGrid), as well as observations of s-process enhancement in AGB stars, planetary nebulae, and barium stars. This comparison shows that the relatively high abundance of 12C in the He-rich intershell in ATON results in an s-process abundance pattern that favours the second over the first s-process peak for all the masses explored. Also, our choice of an advective as opposed to a diffusive numerical scheme for the convective overshoot results in significant s-process nucleosynthesis for the 5 M· models as well, which may be in contradiction with observations.