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Almost all globular clusters (GCs) contain multiple stellar populations consisting of stars with varying helium and light-element abundances. These populations include first-population stars, which exhibit similar chemical compositions as halo-field stars with comparable [Fe/H], and second-population stars, characterized by higher helium and nitrogen abundances along with reduced levels of oxygen and carbon. Nowadays, one of the most intriguing open questions about GCs pertains to the formation and evolution of their multiple populations. Recent works based on N-body simulations of GCs show that the fractions and characteristics of binary stars can serve as dynamic indicators of the formation period of multiple-population GCs and their subsequent dynamical evolution. Nevertheless, the incidence of binaries among multiple populations is still poorly studied. Moreover, the few available observational studies focus only on the bright stars of a few GCs. We used deep images of the GC 47 Tucanae collected with theJames Webband theHubblespace telescopes to investigate the incidence of binaries among multiple populations of M dwarfs and bright main- sequence stars. To reach this objective, we used UV, optical, and near-infrared filters to construct photometric diagrams that allowed us to disentangle binary systems and multiple populations. Moreover, we compared these observations with a large sample of simulated binaries. In the cluster central regions, the incidence of binaries among first-population stars is only slightly higher than that of second- population stars. In contrast, in the external regions, the majority of the studied binaries (≳85%) are composed of first-population stars. These results are consistent with the GC formation scenarios in which the second-population stars originate in the cluster’s central region, forming a compact and dense stellar group within a more extended system of first-population stars.
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This content will become publicly available on April 1, 2026
Exploring the formation environment and dynamics of multiple stellar populations in globular clusters through binary systems
Aims. Globular clusters (GCs) are known to host distinct stellar populations, characterized by different chemical compositions. Despite extensive research, the origin of these populations remains elusive. According to many formation scenarios, the second population (2P) originated within a compact and denser region embedded in a more extended first population (1P) system. As a result, 2P binaries should be disrupted at a larger rate than 1P binaries. For this reason, binary systems offer valuable insight into the environments in which these stellar populations formed and evolved. Methods. We analyzed the fraction of binaries among 1P and 2P M dwarfs in the outer region of NGC 288 using Hubble Space Telescope data. We combined our results with those from a previous work, where we inferred the fraction of 1P and 2P binaries in the cluster center. Results. In the outer region, we find a predominance of 1P binaries (97−3+1%) compared to 2P binaries (3 ± 1%) corresponding to an incidence of binaries with a mass ratio (i.e., the ratio between the masses of the primary and secondary star) greater than 0.5 equal to 6.4 ± 1.7% for the 1P and 0.3 ± 0.2% for the 2P. These binary fractions and incidences differ from those found in the cluster’s central region, where the 1P and 2P exhibit similar binary incidences and fractions. These results are in general agreement with the predictions of simulations following the evolution of binary stars in multiple-population GCs, starting with a dense 2P subsystem concentrated in the central regions of a 1P system.
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- Award ID(s):
- 2009193
- PAR ID:
- 10626408
- Publisher / Repository:
- Astronomy and Astrophysics
- Date Published:
- Journal Name:
- Astronomy & Astrophysics
- Volume:
- 696
- ISSN:
- 0004-6361
- Page Range / eLocation ID:
- A220
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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