Breaking the dichotomy between typical and anomalous globular clusters: the case of NGC 3201

TL;DR

This paper challenges the traditional classification of globular clusters by analyzing NGC 3201, revealing it possesses unique features that do not fit existing categories, thus bridging the gap between typical and anomalous clusters.

Contribution

The study demonstrates that NGC 3201 exhibits a combination of features from both typical and anomalous globular clusters, suggesting a need to revise current classification schemes.

Findings

NGC 3201 has multiple C-N sequences.

It lacks a broad sub-giant branch.

It does not follow the mass-size relation of dwarf galaxies.

Abstract

We recently discovered that NGC 3201 has characteristics that set it outside the current twofold classification scheme for Galactic globular clusters (GCs). Most GCs are mono-metallic and show light-element abundance variations (e.g., Na-O and C-N anti-correlations); but a minority of clusters also present variations in Fe correlating with s-process element and C+N+O abundances, and they possess multiple C-N sequences. These anomalous GCs also have a broad sub-giant branch (SGB) and follow the same mass-size relation as dwarf galaxies possibly evolving into GCs. We now revealed that NGC 3201 belongs to neither group. It has multiple C-N sequences, but no broad SGB, no strong evidence of a Fe-spread, and it does not follow the mass-size relation.