Impact of T- and ρ-dependent decay rates and new (n,γ) cross-sections on the s process in low-mass asymptotic giant branch stars

¹ Department of Experimental Physics, Institute of Physics, University of Szeged, H-6720 Szeged, Dóm tér 9, Hungary
² Konkoly Observatory, HUN-REN CSFK/RCAES, Konkoly Thege Miklós út 15-17, H-1121 Budapest, Hungary
³ CSFK, MTA Centre of Excellence, Konkoly Thege Miklós út 15-17., H-1121 Budapest, Hungary
⁴ Computer, Computational and Statistical Sciences (CCS) Division, Center for Theoretical Astrophysics, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
⁵ School of Physics and Astronomy, Monash University, VIC 3800, Australia
⁶ ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Clayton, VIC 3800, Australia
⁷ ELTE Eötvös Loránd University, Institute of Physics and Astronomy, Pázmány Péter sétány 1/A, Budapest 1117, Hungary

^⋆ Corresponding author: szanyi.balazs@csfk.org

Received: 20 November 2024
Accepted: 1 March 2025

Abstract

Aims. We study the impact of nuclear input related to weak-decay rates and neutron-capture reactions on predictions for the slow neutron-capture process (s process) in asymptotic giant branch (AGB) stars. We provide the first database of surface abundances and stellar yields of the isotopes heavier than iron from the Monash models.

Methods. We ran nucleosynthesis calculations with the Monash post-processing code for seven stellar structure evolution models of low-mass AGB stars with three different sets of nuclear inputs. The reference set has constant decay rates and represents the set used in the previous Monash publications. The second set contains the temperature and density dependence of β decays and electron captures based on the default rates of nuclear NETwork GENerator (NETGEN). In the third set, we further update 92 neutron-capture rates based on re-evaluated experimental cross sections from the ASTrophysical Rate and rAw data Library. We compare and discuss the predictions of the sets relative to each other in terms of isotopic surface abundances and total stellar yields. We also compare the results to isotopic ratios measured in presolar stardust silicon carbide (SiC) grains from AGB stars.

Results. The new sets of models result in a ∼66% solar s-process contribution to the p-nucleus ¹⁵²Gd, confirming that this isotope is predominantly made by the s process. The nuclear input updates result in predictions for the ⁸⁰Kr/⁸²Kr ratio in the He intershell and surface ⁶⁴Ni/⁵⁸Ni, ⁹⁴Mo/⁹⁶Mo, and ¹³⁷Ba/¹³⁶Ba ratios that are more consistent with the corresponding ratios measured in stardust; however, the new predicted ¹³⁸Ba/¹³⁶Ba ratios are higher than the typical values of the SiC grains. The W isotopic anomalies are in agreement with data from the analyses of other meteoritic inclusions. We confirm that the production of ¹⁷⁶Lu and ²⁰⁵Pb is affected by too large uncertainties in their decay rates from NETGEN.