O, Na, Ba and Eu abundance patterns in open clusters

TL;DR

This study analyzes high-resolution elemental abundances in open clusters and finds no significant chemical differences from field stars, challenging previous claims of Na enhancement and globular cluster-like abundance patterns.

Contribution

It provides a homogenized analysis of Na, O, Ba, and Eu abundances in open clusters, demonstrating the absence of globular cluster-like Na-O anti-correlations in these clusters.

Findings

No significant abundance trends compared to field stars.

Na-enhancement previously reported is due to NLTE effects.

Open clusters do not exhibit globular cluster-like chemical signatures.

Abstract

Open clusters are historically regarded as single-aged stellar populations representative of star formation within the Galactic disk. Recent literature has questioned this view, based on discrepant Na abundances relative to the field, and concerns about the longevity of bound clusters contributing to a selection bias: perhaps long-lived open clusters are chemically different to the star formation events that contributed to the Galactic disk. We explore a large sample of high resolution Na, O, Ba & Eu abundances from the literature, homogenized as much as reasonable including accounting for NLTE effects, variations in analysis and choice of spectral lines. Compared to a template globular cluster and representative field stars, we find no significant abundance trends, confirming that the process producing the Na-O anti-correlation in globular clusters is not present in open clusters. Furthermore, previously reported Na-enhancement of open clusters is found to be an artefact of NLTE effects, with the open clusters matching a subset of chemically tagged field stars.