Multiple Populations in Star Clusters

Understand

We review the multiple population (MP) phenomenon of globular clusters (GCs): i.e., the evidence that GCs typically host groups of stars with different elemental abundances and/or distinct sequences in photometric diagrams.

• Most Galactic and extragalactic clusters exhibit internal variations of He, C, N, O, Na, and Al.
• They host two distinct stellar populations: the first population of stars, which resemble field stars with similar metallicities, and one or more second stellar populations that show the signature of high-temperature H-burning.
• In addition, a sub-sample of clusters hosts stellar populations with different heavy-element abundances.