Comparison of the predicted s-process enrichments from different AGB evolutionary models

We compare predicted enrichments of s-process nucleosynthesis products during the Asymptotic Giant Branch (AGB) from independent theoretical models, focusing on stars with initial masses of 2.0 and 3.0 M_⊙ and near-solar and half-solar metallicities: Z = 0.005–0.015. The motivation for this study, in part, is to compare these predictions with observations of elevated abundances of s-process products in planetary nebulae. We compared abundance enhancements for calculations based on Monash models (Karakas & Lugaro 2016, ApJ, 825, 26), the FRUITY database (Cristallo et al. 2015, ApJS, 219, 40), and more recent calculations based on NuGrid (Battino et al. 2019, MNRAS, 489, 1082), FRANEC (Busso et al. 2021, ApJ, 908, 55) and ATON models (Yagüe López et al. 2022 A&A, 657 A28, and Yagüe López, private communication).Some of these authors present multiple models at a given mass and metallicity with different values for parameters that have the effect of raising or lowering the overall enrichment of s-process products. For example, in the Monash models this variation is parameterized by the mass of the partial mixing zone (PMZ) where protons interact with ¹²C nuclei, producing ¹³C that acts as a major neutron source for the s-process. In the NuGrid models, different amounts of mixing contributed by internal gravity waves (IGW) plays a similar role. We find that the NuGrid models predict similar overall enrichments as the Monash models that adopt a PMZ mass of 1 × 10^-4 M_⊙. However, Kobayashi, Karakas, & Lugaro (2020, ApJ, 900, 179) suggest that Monash models with PMZ masses of 1 × 10^-3 M_⊙ provide better fits to observational data for these masses. These models predict higher s-process enrichments than NuGrid models with and without enhanced IGW for the same initial mass and metallicity. Enrichments reported in the FRUITY online database (http://fruity.oa-teramo.inaf.it/) are similar to those of the preferred Monash models, especially for 2.0 M_⊙. In addition, results from the ATON and more recent FRANEC models both exhibit lower overall enrichments than Monash and FRUITY, but similarly higher enrichments than the NuGrid models. This study illustrates the range of theoretical abundance enhancements predicted by codes that model internal mixing, convection, and mass loss AGB stars differently, which can be compared with observed elemental abundances in evolved stars and planetary nebulae. This work was supported by NSF grant AST 1715332.