Chemical tagging of three distinct populations of red giants in the globular cluster NGC 6752

TL;DR

This study identifies three distinct stellar populations in the globular cluster NGC 6752 based on aluminium, magnesium, and silicon abundances, revealing complex chemical evolution and multiple polluters.

Contribution

It provides the first detailed chemical tagging of three populations in NGC 6752 using homogeneous abundance measurements and links these to photometric sequences.

Findings

Three distinct Al abundance groups identified

Correlations and anticorrelations among key elements observed

Different polluters are required for the intermediate population

Abstract

We present aluminium, magnesium, and silicon abundances in the metal-poor globular cluster NGC 6752 for a sample of more than 130 red giants with homogeneous oxygen and sodium abundances. We find that [Al/Fe] shows a spread of about 1.4 dex among giants in NGC 6752 and is anticorrelated with [Mg/Fe] and [O/Fe] and correlated with [Na/Fe] and [Si/Fe]. These relations are not continuous in nature, but the distribution of stars is clearly clustered around three distinct Al values, low, intermediate, and high. These three groups nicely correspond to the three distinct sequences previously detected using Stromgren photometry along the red giant branch. These two independent findings strongly indicate the existence of three distinct stellar populations in NGC 6752. Comparing the abundances of O and Mg, we find that the population with intermediate chemical abundances cannot originate from material with the same composition of the most O- and Mg-poor population, diluted by material with that of the most O- and Mg-rich one. This calls for different polluters.