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

¹ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Eötvös Loránd Research Network (ELKH), Konkoly Thege Miklós út 15-17, 1121 Budapest, Hungary
e-mail: andres.yague@csfk.org
² Instituto de Astrofísica de Canarias, C/Via Láctea s/n, 38205 La Laguna, Spain
³ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Spain
⁴ INAF-Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio, Italy
⁵ School of Physics and Astronomy, Monash University, Clayton, VIC 3800, Australia
⁶ ELTE Eötvös Loránd University, Institute of Physics, Pázmány Péter sétány 1/A, Budapest 1117, Hungary
⁷ X Computational Physics (XCP) Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
⁸ Computer, Computational and Statistical Sciences (CCS) Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA

Received: 1 September 2020
Accepted: 20 September 2021

Abstract

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.