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1. A JWST project on 47 Tucanae: Kinematics, energy equipartition, and anisotropy of multiple populations

   https://doi.org/10.1051/0004-6361/202554038  

   Ziliotto, T; Milone, A P; Cordoni, G; Aros, F I; Vesperini, E; Lee, J-W; Bellini, A; Bianchini, P; Mastrobuono-Battisti, A; Libralato, M; et al (June 2025, Astronomy & Astrophysics)

   Recent work withJWSThas demonstrated its capability to identify and chemically characterize multiple populations in globular clusters down to the H-burning limit. In this study, we explore the kinematics of multiple populations in the globular cluster 47 Tucanae by combining data fromJWST, HST, Gaia, and ground-based telescopes. We analyzed velocity dispersion and anisotropy profiles from the cluster center out to ∼10R_h. Our findings indicate that while first population (1G) stars’ motions are isotropic, second population (2G) stars’ motions are significantly radially anisotropic. These results align with the predictions of simulations of the dynamical evolution of clusters where 2G stars are initially more centrally concentrated than 1G stars. Furthermore, we subdivided the 2G population into two subpopulations: 2G_Aand 2G_B, with the latter being more chemically extreme. We compared their dynamical profiles and found no significant differences. For the first time, we measured the degree of energy equipartition among the multiple populations of 47 Tucanae. Overall, within the analyzed radial range (∼2–4R_h), both populations exhibit a low degree of energy equipartition. The most significant differences between 1G and 2G stars are observed in the tangential velocity component, where 2G stars are characterized by a stronger degree of energy equipartition than 1G stars. In the radial component, the behavior of 1G and 2G stars is more variable, with differences largely dependent on radius. Moreover, our analysis reveals that the ratio of rotational velocity to velocity dispersion is larger for the 2G population. Finally, we found that 1G stars exhibit a higher skewness in their tangential proper motions than 2G stars, providing additional evidence of kinematic differences between the two stellar generations. 

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2. Blanco DECam Bulge Survey (BDBS). VII. Multiple Populations in Globular Clusters of the Galactic Bulge

   https://doi.org/10.3847/1538-4357/ac94c5  

   Kader, Justin A.; Pilachowski, Catherine A.; Johnson, Christian I.; Rich, R. Michael; Young, Michael D.; Simion, Iulia T.; Clarkson, William I.; Michael, Scott; Kunder, Andrea; Vivas, Anna Katherina; et al (November 2022, The Astrophysical Journal)

   Abstract We present photometric evidence for multiple stellar populations (MPs) in 14 globular clusters (GCs) toward the southern Galactic bulge. The photometric data come as part of the Blanco DECam Bulge Survey, which is a deep, wide-field near-UV-near-IR ( ugriz Y) survey of the southern Galactic bulge. Here, we present the first systematic study of bulge GC multiple populations with deep photometry including the u band, which is a crucial indicator of the abundance of CNO-bearing molecules in stellar atmospheres. We identify cluster members using Gaia EDR3 proper motion measurements, and then isolate red giant branch stars using r versus u − r color–magnitude diagrams. We find evidence suggesting all 14 clusters host at least two populations, and NGC 6441, NGC 6626, and NGC 6656 appear to have at least three populations. Many of these clusters are not part of the Hubble Space Telescope (HST) surveys nor do they have comprehensive spectroscopic analyses so we are presenting the first evidence of MPs in several clusters. Not only do we find a strong anticorrelation between the fraction of first-generation stars and cluster absolute V magnitude, but the correlation coefficient and cluster-to-cluster scatter are similar to the results obtained from HST. Our ground-based data extend to much larger radial distances than similar HST observations, enabling a reliable estimate of the global fraction of first-generation stars in each cluster. This study demonstrates that ground-based u -band photometry as provided by DECam will prove powerful in the study of multiple populations in resolved GCs. 

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3. The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XXIV. Differences in Internal Kinematics of Multiple Stellar Populations

   https://doi.org/10.3847/1538-4357/acaec6  

   Libralato, Mattia; Vesperini, Enrico; Bellini, Andrea; Milone, Antonino P.; van der Marel, Roeland P.; Piotto, Giampaolo; Anderson, Jay; Aparicio, Antonio; Barbuy, Beatriz; Bedin, Luigi R.; et al (February 2023, The Astrophysical Journal)

   Abstract Our understanding of the kinematic properties of multiple stellar populations (mPOPs) in Galactic globular clusters (GCs) is still limited compared to what we know about their chemical and photometric characteristics. Such limitation arises from the lack of a comprehensive observational investigation of this topic. Here we present the first homogeneous kinematic analysis of mPOPs in 56 GCs based on high-precision proper motions computed with Hubble Space Telescope data. We focused on red-giant-branch stars, for which the mPOP tagging is clearer, and measured the velocity dispersion of stars belonging to first (1G) and second generations (2G). We find that 1G stars are generally kinematically isotropic even at the half-light radius, whereas 2G stars are isotropic at the center and become radially anisotropic before the half-light radius. The radial anisotropy is induced by a lower tangential velocity dispersion of 2G stars with respect to the 1G population, while the radial component of the motion is comparable. We also show possible evidence that the kinematic properties of mPOPs are affected by the Galactic tidal field, corroborating previous observational and theoretical results suggesting a relation between the strength of the external tidal field and some properties of mPOPs. Although limited to the GCs’ central regions, our analysis leads to new insights into the mPOP phenomenon, and provides the motivation for future observational studies of the internal kinematics of mPOPs. 

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4. JWST imaging of the closest globular clusters: III. Multiple populations along the low-mass main-sequence stars of NGC 6397

   https://doi.org/10.1051/0004-6361/202450589  

   Scalco, M; Libralato, M; Gerasimov, R; Bedin, L R; Vesperini, E; Nardiello, D; Bellini, A; Griggio, M; Apai, D; Salaris, M; et al (September 2024, Astronomy & Astrophysics)

   Thanks to its exceptional near-infrared photometry, JWST can effectively contribute to the discovery, characterisation, and understanding of multiple stellar populations in globular clusters, especially at low masses where theHubbleSpace Telescope (HST) faces limitations. This paper continues the efforts of the JWST GO-1979 programme in exploring the faintest members of the globular cluster NGC 6397. In this work, we show that the combination of HST and JWST data allows us to identify two groups of MS stars: MSa, the first-generation group, and MSb, the second-generation group. We measured the ratio between the two groups and combined it with measurements from the literature focused on more central fields and more massive stars compared to our study. Our findings suggest that the MSa and MSb stars are present in a ≈30−70 ratio regardless of the distance from the centre of the cluster and the mass of the stars used so far. However, considering the limited areal coverage of our study, a more comprehensive spatial analysis is necessary to definitively confirm complete spatial mixing. 

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5. The HST Large Programme on NGC 6752 ‐ V. Differences in luminosity and mass function among stellar populations

   https://doi.org/10.1002/asna.20240018  

   Scalco, Michele; Gerasimov, Roman; Bedin, Luigi_R; Vesperini, Enrico; Nardiello, Domenico; Salaris, Maurizio; Burgasser, Adam; Anderson, Jay; Libralato, Mattia; Bellini, Andrea; et al (March 2024, Astronomische Nachrichten)

   Abstract We exploit the astro‐photometric dataset of the multi‐epoch infrared parallel field of aHubble Space TelescopeLarge Programme aimed at studying the faintest stars of the globular cluster NGC 6752 to determine the luminosity and mass functions of the multiple stellar populations of this cluster. Thanks to the measurement of proper motions and deeper completeness, the results presented in this paper represent a significant improvement over those of previous studies. We successfully derived membership probabilities reaching stars as faint as , allowing us to reliably distinguish the three main stellar populations detected within this cluster. We employed a new set of model isochrones that have been individually fit to the colour–magnitude diagram of each population. We present a comprehensive analysis of the luminosity and mass functions for three stellar populations within NGC 6752. Notably, our findings reveal differences in the present‐day luminosity and mass functions of first‐generation and second‐generation stars; these differences are consistent with the manifestation of the effects of dynamical processes acting on populations with different initial spatial distributions. Finally, we publicly release the catalogues with positions, photometry, proper motions and memberships probabilities, as well as the stacked‐image atlases and all newly calculated stellar models. 

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