Spectroscopic analysis of the bulge Globular Cluster ESO~456-SC38

TL;DR

This study analyzes the chemical composition and stellar populations of the bulge globular cluster ESO 456-SC38 using spectroscopic data, confirming multiple populations and cluster membership of RR Lyrae stars.

Contribution

It provides the first alpha abundance measurements for seven stars in ESO 456-SC38 and confirms the cluster's stellar membership using Gaia and radial velocity data.

Findings

Presence of multiple stellar populations indicated by abundance spreads

Confirmed RR Lyrae stars are members of the cluster

First spectroscopic alpha abundances for this cluster

Abstract

It has been suggested that the oldest stellar populations in the Milky Way Galaxy are tightly bound and confined to the central regions of the Galaxy. This is one of the reasons why a handful of globular clusters located in the bulge region are thought to be remnants of the primeval formation stages of the Milky Way. The globular cluster, ESO 456-SC38 (Djorgovski~2) is one such cluster; it has a blue horizontal branch, is projected very close to the center of the Galaxy, and has an orbit confining it to the bulge/bar region. The first alpha abundances of seven stars in this heavily reddened cluster are presented using APOGEE DR16. A significant spread in the abundances of N, C, Na, and Al indicates the presence of multiple stellar populations in this cluster. Using Gaia DR2 proper motions and radial velocities from BRAVA-RR, we confirm RR Lyrae stars belong to this globular cluster.