CN Variations in High Metallicity Globular and Open Clusters

TL;DR

This study compares CN bandstrength variations in high-metallicity globular and open clusters, revealing that globular clusters exhibit star-to-star abundance variations while open clusters do not, highlighting environmental influences on cluster formation.

Contribution

It demonstrates that high-metallicity globular clusters show bimodal CN variations similar to halo clusters, unlike open clusters, emphasizing environmental effects on chemical inhomogeneities.

Findings

Globular clusters have broad, bimodal CN distributions.

Open clusters have narrow, unimodal CN distributions.

Environmental factors influence cluster chemical enrichment.

Abstract

We present a comparison of CN bandstrength variations in the high-metallicity globular clusters NGC 6356 and NGC 6528 with those measured in the old open clusters NGC 188, NCG 2158 and NGC 7789. Star-to-star abundance variations, of which CN differences are a readily observable sign, are commonplace in moderate-metallicity halo globular clusters but are unseen in the field or in open clusters. We find that the open clusters have narrow, unimodal distributions of CN bandstrength, as expected from the literature, while the globular clusters have broad, bimodal distributions of CN bandstrength, similar to moderate-metallicity halo globular clusters. This result has interesting implications for the various mechanisms proposed to explain the origin of globular cluster abundance inhomogeneities, and suggests that the local environment at the epoch of cluster formation plays a vital role in regulating intracluster enrichment processes.