Multiple stellar populations in the Galactic globular cluster NGC 6752

TL;DR

This study uses high-precision HST and ground-based photometry to identify multiple stellar populations in NGC 6752, revealing a broadened main sequence and chemical abundance variations among red-giant stars.

Contribution

It provides evidence of multiple stellar populations in NGC 6752 through photometric broadening and chemical correlations, advancing understanding of globular cluster complexity.

Findings

Broadened main sequence not due to binaries or errors

Indication of main-sequence split

Red-giant branch shows Na and O abundance variations

Abstract

We have carried out high-precision photometry on a large number of archival HST images of the Galactic globular cluster NGC 6752, to search for signs of multiple stellar populations. We find a broadened main sequence, and demonstrate that this broadening cannot be attributed either to binaries or to photometric errors. There is also some indication of a main-sequence split. No significant spread could be found along the subgiant branch, however. Ground-based photometry reveals that in the U vs. (U-B) color-magnitude diagram the red-giant branch exhibits a clear color spread, which we have been able to correlate with variations in Na and O abundances. In particular the Na-rich, O-poor stars identified by Carretta et al. (2007) define a sequence on the red side of the red-giant branch, while Na-poor, O-rich stars populate a bluer, more dispersed portion of the red-giant branch.