Observational constraints on the origin of the elements. VI. Origin and evolution of neutron-capture elements as probed by the Gaia-ESO survey

TL;DR

This study uses Gaia-ESO survey data and Galactic chemical evolution models to investigate the origins of neutron-capture elements, revealing insights into the timescales and astrophysical sites responsible for their synthesis.

Contribution

It provides observational constraints on neutron-capture element origins, highlighting the need for short delay r-process sites and suggesting possible overestimation of s-process efficiency in current models.

Findings

Short delay times for Eu production are suggested by [Eu/Fe]-[Fe/H] data.

Inconsistencies exist between NS-NS merger models and observed Eu abundances.

Current AGB models may overestimate s-process efficiency in low-mass stars.

Abstract

Most heavy elements beyond the iron peak are synthesized via neutron capture processes. The nature of the astrophysical sites of neutron capture processes is still very unclear. In this work we explore the observational constraints of the chemical abundances of s-process and r-process elements on the sites of neutron-capture processes by applying Galactic chemical evolution (GCE) models to the data from Gaia-ESO large spectroscopic stellar survey. For the r-process, the [Eu/Fe]-[Fe/H] distribution suggests a short delay time of the site that produces Eu. Other independent observations (e.g., NS-NS binaries), however, suggest a significant fraction of long delayed ($>1$Gyr) neutron star mergers (NSM). When assuming NSM as the only r-process sites, these two observational constraints are inconsistent at above 1$\sigma$ level. Including short delayed r-process sites like magneto-rotational supernova can resolve this inconsistency. For the s-process, we find a weak metallicity dependence of the [Ba/Y] ratio, which traces the s-process efficiency. Our GCE model with up-to-date yields of AGB stars qualitatively reproduces this metallicity dependence, but the model predicts a much higher [Ba/Y] ratio compared to the data. This mismatch suggests that the s-process efficiency of low mass AGB stars in the current AGB nucleosynthesis models could be overestimated.