Mixing and Magnetic Fields in Asymptotic Giant Branch Stars in the Framework of FRUITY Models

Abstract

In the last few years, the modeling of asymptotic giant branch (AGB) stars has been much investigated, both focusing on nucleosynthesis and stellar evolution aspects. Recent advances in the input physics required for stellar computations made it possible to construct more accurate evolutionary models, which are an essential tool to interpret the wealth of available observational and nucleosynthetic data. Motivated by such improvements, the FUNS stellar evolutionary code has been updated. Nonetheless, mixing processes occurring in AGB stars’ interiors are currently not well-understood. This is especially true for the physical mechanism leading to the formation of the 13C pocket, the major neutron source in low-mass AGB stars. In this regard, post-processing s-process models assuming that partial mixing of protons is induced by magneto-hydrodynamics processes were shown to reproduce many observations. Such mixing prescriptions have now been implemented in the FUNS code to compute stellar models with fully coupled nucleosynthesis. Here, we review the new generation of FRUITY models that include the effects of mixing triggered by magnetic fields by comparing theoretical findings with observational constraints available either from the isotopic analysis of trace-heavy elements in presolar grains or from carbon AGB stars and Galactic open clusters.

The Gaia-ESO survey: Mapping the shape and evolution of the radial abundance gradients with open clusters

“…The average [s/Fe] gra-dient does not show a remarkable variation with age in the inner region, while in the outer regions the youngest clusters are more enriched in s-process elements. This is likely due to the different timescales of their production and to the strong metallicity dependence of their yields (Casali et al 2020b;Magrini et al 2021b;Vescovi 2021;Viscasillas Vázquez et al 2022). In the [s/Fe] plane the separation between the three age bins is clearer and is driven by the differences in [Fe/H] of the clusters.…”

“…Carraro et al 2007;Yong et al 2012). A few years later, the era of large spectroscopic surveys started, also aimed at complementing the subsequent exploitation of the data coming from the Gaia satellite, which was launched in 2013 (Gaia Collaboration et al 2016b,a, 2018, 2021. Among these the Gaia-ESO survey (Gilmore et al 2012(Gilmore et al , 2022Randich et al 2013Randich et al , 2022, the only one performed on a 8m class telescope, put a specific focus on the Galactic population of OCs; Gaia-ESO targeted OCs over a wide range of ages, distances, masses, and metallicities, observing large unbiased samples of cluster candidates, with a well-defined selection function (Bragaglia et al 2022;Randich et al 2022).…”

Production of solar abundances for nuclei beyond Sr: The s- and r-process perspectives

“…These works deal with the particular approach that considers the buoyancy of magnetic flux tubes in a stellar dynamo process as responsible for the deep mixing episodes mentioned in Section 1 (see Nordhaus et al, 2008;Denissenkov et al, 2009). This idea led to analytical models of the underlying physical mechanisms in terms of 3D solutions for the magneto-hydrodynamic (MHD) equations involved (Nucci and Busso, 2014), where the previously quoted recent upgrades were obtained with the help of full stellar models (Vescovi et al, 2020;Vescovi, 2021), subsequently integrated by post-process computations, derived with the aim of reproducing the relevant physical parameters without recomputing the energy generation (Busso et al, 2021). In those attempts, comparisons were presented between model predictions and some major available constraints to sprocessing (from high-resolution spectroscopy of selected classes of evolved stars to the S.S. abundances as emerging from the chemical evolution of the Galaxy and to isotopic admixtures of heavy elements, as measured in presolar grains recovered in pristine meteorites).…”