Observing multiple populations in globular clusters with the ESO archive: NGC 6388 reloaded

TL;DR

This study uses ESO archive data to analyze multiple stellar populations in the globular cluster NGC 6388, revealing distinct chemical groups and insights into the polluters responsible for these populations.

Contribution

It provides the first detailed chemical analysis of NGC 6388's multiple populations using high-resolution spectra from archival data.

Findings

No significant metallicity dispersion in NGC 6388.

Identification of three discrete stellar populations based on chemical abundances.

Evidence suggesting multiple polluter classes contributed to the cluster's chemical diversity.

Abstract

The metal-rich and old bulge globular cluster (GC) NGC 6388 is one of the most massive Galactic GCs (M ~ 10^6 Msun). However, the spectroscopic properties of its multiple stellar populations rested only on 32 red giants (only seven of which observed with UVES, the remaining with GIRAFFE), given the difficulties in observing a rather distant cluster, heavily contaminated by bulge and disc field stars. We bypassed the problem using the largest telescope facility ever: the European Southern Observatory (ESO) archive. By selecting member stars identified by other programmes, we derive atmospheric parameters and the full set of abundances for 15 species from high resolution UVES spectra of another 17 red giant branch stars in NGC 6388. We confirm that no metallicity dispersion is appreciable in this GC. About 30% of stars show the primordial composition of first generation stars, about 20% present an extremely modified second generation composition, and half of the stars has an intermediate composition. The stars clearly distribute in the Al-O and Na-O planes into three discrete groups. We find substantial hints that more than a single class of polluters is required to reproduce the composition of the intermediate component in NGC 6388. In the heavily polluted component the sum Mg+Al increases as Al increases. The sum Mg+Al+Si is constant, and is the fossil record of hot H-burning at temperatures higher than about 70 MK in the first generation polluters that contributed to form multiple populations in this cluster.