Multiple Populations in Low-mass Globular Clusters: Eridanus

TL;DR

This study investigates multiple stellar populations in the low-mass globular cluster Eridanus, providing evidence of MPs at lower masses and exploring the potential mass threshold for their formation.

Contribution

It presents the first detailed chemical abundance analysis of Eridanus, indicating MPs in a low-mass cluster and suggesting a possible mass threshold for MP development.

Findings

Significant nitrogen abundance dispersion indicates MPs in Eridanus.

Lower mass limit for MPs estimated around log Minitial ~4.98-5.26.

Trend of increasing initial mass with cluster age observed.

Abstract

Multiple populations (MPs), characterized by variations in light elemental abundances, have been found in stellar clusters in the Milky Way, Magellanic Clouds, as well as several other dwarf galaxies. Based on a large amount of observations, mass has been suggested to be a key parameter affecting the presence and appearance of MPs in stellar clusters. To further investigate the existence of MPs in low-mass clusters and explore the mass threshold for MP formation, we carried out a project studying the stellar population composition in several low-mass Galactic globular clusters. Here we present our study on the cluster Eridanus. With blue-UV low-resolution spectra obtained with the OSIRIS/Multi-object spectrograph on the Gran Telescopio Canarias, we computed the spectral indices of CH and CN for the sample giant stars, and derived their carbon and nitrogen abundances using model spectra. A significant dispersion in the initial surface abundance of nitrogen was found in the sample, indicating the existence of MPs in Eridanus. Inspecting the age-initial mass distribution of in-situ clusters with MPs, we find a slight trend that initial mass increases with increasing age, and the lowest initial mass of log Minitial ~4.98 and 5.26 are found at the young and old end, respectively, which might provide a rough reference for the mass threshold for clusters to form MPs. However, more observations of clusters with low initial masses are still necessary before any firm conclusion can be drawn.