No evidence for multiple stellar populations in the low-mass Galactic globular cluster E 3

TL;DR

This study finds no evidence of multiple stellar populations in the low-mass globular cluster E 3, suggesting it is a genuine single stellar population, unlike most Galactic globular clusters.

Contribution

It provides the first clear evidence of a low-mass globular cluster with no signs of self-enrichment or multiple populations.

Findings

CN abundance is unimodal in E 3

E 3 shows no signs of multiple stellar populations

E 3 is likely a single stellar population globular cluster

Abstract

Multiple stellar populations are a widespread phenomenon among Galactic globular clusters. Even though the origin of the enriched material from which new generations of stars are produced remains unclear, it is likely that self-enrichment will be feasible only in clusters massive enough to retain this enriched material. We searched for multiple populations in the low mass (M~1.4 x 10^4 M_sun) globular cluster E 3, analyzing SOAR/Goodman multi-object spectroscopy centered on the blue CN absorption features of 23 red giant branch stars. We find that the CN abundance does not present the typical bimodal behavior seen in clusters hosting multi stellar populations, but rather a unimodal distribution that indicates the presence of a genuine single stellar population, or a level of enrichment much lower than in clusters that show evidence for two populations from high-resolution spectroscopy. E 3 would be the first bona fide Galactic old globular cluster where no sign of self-enrichment is found.