Justin Kader, 2022
Title: Multiple Populations in Globular Clusters of the Galactic Bulge
Abstract: Globular clusters (GCs) are compact assemblages of up to several million stars bound by gravity. The stellar populations of GCs are metal-poor (-2<[Fe/H]<0) and old, with ages comparable to the age of the universe. While these and other basic aspects of GCs are well established, more recent observations have revealed unexpected complexity. One example was the discovery of chemical abundance variations among the unevolved stars in several Galactic GCs, suggesting these clusters are composed of at least two stellar populations formed perhaps a few hundred million years apart. The discovery of multiple populations represented a paradigm shift, since GCs had been regarded as archetypical single-age, mono-metallicity, chemically homogeneous stellar populations. In the roughly 20 years since this discovery, it has been demonstrated that almost all Galactic halo GCs harbor multiple stellar populations.
I focus on the stellar populations of the GCs in the Galactic bulge. These clusters have eluded close scrutiny because of extinction and reddening along their sightlines caused by interstellar dust, and because of the astrometric confusion caused by the high degree of stellar crowding in the bulge fields that these clusters inhabit. If obscurity of these clusters alone were not enough to make them tantalizing targets of study, their basic properties and proximity to the bulge warrant attention as well. The GCs of the Galactic bulge have higher metallicity than their halo counterparts for reasons that are not well understood, and there are similarities between their stars and the stars belonging to the bulge. It is possible that the evolution of these GCs is inextricably related to the assembly of the Galactic bulge itself. A detailed understanding of the stellar populations in these clusters is needed to assemble a coherent picture of the joint evolution of the bulge GCs and the bulge itself.