A MUSE view on the formation of multiple populations in Globular Clusters: Observational constraints from chemistry, binaries, and kinematics

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As part of the Guaranteed Time Observations with the integral field spectrograph MUSE, we have observed the central regions of 26 Galactic Globular clusters (GCs) at multiple epochs, thus collecting more than 2 million individual stellar spectra. This invaluable dataset has been used by our group to characterize, for example, kinematics, binarity, and metallicity properties of individual clusters. An intriguing aspect of globular clusters is the presence of so-called multiple populations. For a long time, GCs have been considered perfect examples of a single stellar population consisting of stars having the same age and the same chemical composition. However, upon closer inspection, the situation appears to be more complex. It has now been shown that almost all GCs older than 2 Gyrs contain multiple populations, albeit with various properties. The stars belonging to the different populations are characterized by varying abundances of certain elements (e.g., N, O, Na) following particular correlations. By combining the information inferred from the photometric colors of red giant branch (RGB) stars with their spectroscopic properties from the MUSE spectra, we will investigate the chemical, kinematic, and binary properties of the populations in GCs included in our survey. In a first time, we will focus our efforts to make a thorough analysis of four priority clusters, NGC 1851, NGC 6752, NGC 7078, and Omega Centauri. This sample of clusters is representative of different phenomena linked to multiple populations, ranging from ``bona fide'' GCs consisting of two main populations to more complex clusters with alleged (NGC 1851) and confirmed (NGC 5139) iron spreads. In a second time, we will work on the remaining 16 clusters for which we have the photometry needed to separate the population. Work on these clusters includes optimizing the separation of RGB stars into their respective populations, comparing binary fractions between populations, and quantifying iron-spread in metal-complex clusters Our work will provide new observational constraints on key aspects that will help to better understand the origin of multiple populations in GCs. This is still an open debate where theories are numerous and characterizing populations' properties homogeneously is most helpful to constrain some of the formation scenarios.