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The presence of more than one stellar population in globular clusters (GCs) is one of the most fascinating recent discoveries in the field of stellar populations. Yet, the phenomenon remains an enigma. For old Milky Way clusters, the properties of the different populations of stars are constrained by chemical abundances coupled with the nicknamed Chromosome Maps photometric diagram. By using these maps we have identified two main classes of GCs: Type I, including ∼83% of the objects, and Type II clusters. Both classes host two main groups of stars, referred to as first and second population. Different stellar populations in GCs are characterized by distinct chemical abundances in specific elements, whose knowledge keeps fundamental information on the processes occurring in the early stages of life of these ancient stellar systems. One of the most intriguing results from studies based on chemical abundances is that, contrary to what commonly believed, some GCs, besides Omega Centauri, harbour stellar populations with different metallicity. The fraction of these clusters might be high as suggested by the Type II morphologies of the Chromosome Maps.
I will present the latest results on how to read the Chromosome Maps in terms of chemical abundances. I will focus on the most intriguing features observed on the maps, namely their variety and the features that can be interpreted as proxies of metallicity variations. I will discuss the impact of these results in the context of GC formation and the assembly of the Galaxy.
To view this talk, please go to: https://youtu.be/DUKyDidiJbc