New Neutron-Capture Measurements in 23 Open Clusters. I. The R-Process

TL;DR

This study measures neutron-capture element abundances in 23 open clusters to understand their nucleosynthesis origins and Galactic distribution, revealing age and spatial trends for r- and s-process elements.

Contribution

It provides a homogeneous analysis of multiple neutron-capture elements across open clusters, highlighting their abundance trends with age and Galactic position.

Findings

Pure r-process elements increase with cluster age.

Mixed r- and s-process elements show no significant age trend.

Several elements exhibit gradients of ~0.04 dex/kpc across the Galaxy.

Abstract

Neutron-capture elements, those with Z > 35, are the least well-understood in terms of nucleosynthesis and formation environments. The rapid neutron-capture, or r-process, elements are formed in the environments and/or remnants of massive stars, while the slow neutron-capture, or s-process, elements are primarily formed in low-mass AGB stars. These elements can provide much information about Galactic star formation and enrichment, but observational data is limited. We have assembled a sample of 68 stars in 23 open clusters that we use to probe abundance trends for six neutron-capture elements (Eu, Gd, Dy, Mo, Pr, and Nd) with cluster age and location in the disk of the Galaxy. In order to keep our analysis as homogenous as possible, we use an automated synthesis fitting program, which also enables us to measure multiple (3-10) lines for each element. We find that the pure r-process elements (Eu, Gd, and Dy) have positive trends with increasing cluster age, while the mixed r- and s- process elements (Mo, Pr, and Nd) have insignificant trends consistent with zero. Pr, Nd, Eu, Gd, and Dy have similar, slight (though mostly statistically significant) gradients of ~0.04 dex/kpc. The mixed elements also appear to have nonlinear relationships with Galactocentric radius.