Multiple stellar populations in globular clusters: exploring the low mass regime with JWST

This thesis presents a comprehensive study of multiple stellar populations and their internal kinematics in several Galactic globular clusters (GCs), aiming to deepen our understanding of their complex formation and evolutionary histories. Using state-of-the-art multi-band photometry from the Hubble Space Telescope (HST) and the James Webb Space Telescope (JWST), this work probes detailed chemical and dynamical signatures across broad ranges of stellar mass and cluster radius. The first part examines M 92, a metal-poor GC ([Fe/H] = –2.3), through ultraviolet, optical, and infrared photometry spanning over 20 HST and JWST filters. This analysis reveals multiple populations among K- and M-dwarf stars with measurable helium and oxygen abundance differences, extending chemical complexity deep into the low-mass main sequence. Proper motion analysis shows isotropic motions within ~2 half-light radii, consistent with the cluster’s old dynamical age. Importantly, the oxygen variations among M-dwarfs mirror those of more massive stars, contradicting single-generation accretion scenarios and supporting multiple star-formation episodes that uniformly affected stars across the full mass range. Additionally, JWST NIRCam proves highly effective in detecting oxygen variations in M-dwarfs, underscoring its utility for studying metal-poor clusters. The second study focuses on 47 Tucanae, a Type I GC with well-defined populations. By combining multi-epoch HST and JWST proper motions with Gaia data, the dynamics of first- and second-generation stars are characterized from the RGB to the hydrogen-burning limit. Second-generation stars exhibit higher energy equipartition and more pronounced radial anisotropy, consistent with models in which these stars formed more centrally concentrated and dynamically evolved within a first-generation halo. These results provide new empirical constraints on GC dynamical evolution. The final study investigates Omega Centauri, the most massive and chemically complex Type II GC, using HST and JWST data to explore kinematics in the radial range ~0.9–2.3 half-light radii. Chromosome maps reveal two main streams: lower-stream (LS) stars with first-population chemistry, and upper-stream (US) stars chemically analogous to second population stars. The populations display distinct kinematics: US stars show strong radial anisotropy due to lower tangential velocity dispersion, while LS stars are nearly isotropic. A gradient in anisotropy appears among chemically extreme US subpopulations, highlighting a link between chemical enrichment and dynamical state. Angular momentum dispersion and higher-order moment analyses further distinguish the groups, with LS stars showing greater angular momentum dispersion and velocity skewness. While Omega Centauri is chemically a Type II GC, its kinematic properties resemble those of Type I clusters, pointing to similar formative and evolutionary processes. Together, these studies provide compelling evidence for multiple star formation episodes in individual GCs, challenge monolithic formation scenarios, and highlight the interplay between chemical and dynamical evolution. This research strengthens our understanding of GCs as key tracers of Galactic halo assembly and early cosmic history, while offering new observational benchmarks for models of cluster formation and evolution.