Evidence for Enrichment by Supernovae in the Globular Cluster NGC 6273

TL;DR

This study uses combined photometry and spectroscopy to identify supernovae enrichment signatures in the globular cluster NGC 6273, revealing distinct subpopulations with different chemical compositions.

Contribution

It demonstrates a method to detect supernovae enrichment in globular clusters and applies it to NGC 6273, showing evidence of multiple chemical populations.

Findings

Identification of two distinct subpopulations with different calcium abundances.

The Ca-rich subpopulation is also enhanced in CN and CH, showing positive correlations.

NGC 6273 likely retained supernova ejecta, indicating a massive, complex chemical evolution.

Abstract

In our recent investigation (Lim et al. 2015), we have shown that narrow-band photometry can be combined with low-resolution spectroscopy to effectively search for globular clusters (GCs) with supernovae (SNe) enrichments. Here we apply this technique to the metal-poor bulge GC NGC 6273, and find that the red giant branch stars in this GC are clearly divided into two distinct subpopulations having different calcium abun- dances. The Ca rich subpopulation in this GC is also enhanced in CN and CH, showing a positive correlation between them. This trend is identical to the result we found in M22, suggesting that this might be a ubiquitous nature of GCs more strongly affected by SNe in their chemical evolution. Our results suggest that NGC 6273 was massive enough to retain SNe ejecta which would place this cluster in the growing group of GCs with Galactic building block characteristics, such as {\omega} Centauri and Terzan 5.