Mixed Populations in Globular Clusters: Et Tu, 47 Tuc?

TL;DR

This study uses HST archival images to identify multiple stellar populations in 47 Tuc, revealing a complex subgiant branch and a broadened main sequence indicative of multiple generations of stars.

Contribution

It provides detailed evidence of multiple populations in 47 Tuc through analysis of the subgiant branch and main sequence, highlighting spatial variations within the cluster.

Findings

Subgiant branch shows a luminosity spread with at least two components.

Main sequence broadening increases with fainter magnitudes.

Approximately 10% of stars are in a fainter subgiant component.

Abstract

We exploit the large number of archival HST images of 47 Tuc to examine its subgiant branch (SGB) and main sequence (MS) for signs of multiple populations. In the cluster core, we find that the cluster's SGB exhibits a clear spread in luminosity, with at least two distinct components: a brighter one with a spread that is real but not bimodal, and a second one about 0.05 mag fainter, containing about 10% of the stars. In a less crowded field 6 arcminutes from the center, we find that the MS is broadened much more than can be accounted for by photometric errors, and that this broadening increases at fainter magnitudes.