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تسجيل مستخدم جديدGaia and Hubble unveil the kinematics of stellar populations in the Type II globular clusters {omega} Centauri and M 22
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The origin of multiple stellar populations in Globular Clusters (GCs) is one of the greatest mysteries of modern stellar astrophysics. N-body simulations suggest that the present-day dynamics of GC stars can constrain the events that occurred at high redshift and led to the formation of multiple populations. Here, we combine multi-band photometry from the Hubble Space Telescope (HST) and ground-based facilities with HST and Gaia Data Release 2 proper motions to investigate the spatial distributions and the motions in the plane of the sky of multiple populations in the type II GCs NGC 5139 ($omega,$Centauri) and NGC 6656 (M 22). We first analyzed stellar populations with different metallicities. Fe-poor and Fe-rich stars in M 22 share similar spatial distributions and rotation patterns and exhibit similar isotropic motions. Similarly, the two main populations with different iron abundance in $omega,$Centauri share similar ellipticities and rotation patterns. When analyzing different radial regions, we find that the rotation amplitude decreases from the center towards the external regions. Fe-poor and Fe-rich stars of $omega,$Centauri are radially anisotropic in the central region and show similar degrees of anisotropy. We also investigate the stellar populations with different light-element abundances and find that their N-rich stars exhibit higher ellipticity than N-poor stars. In $omega,$Centauri Centauri both stellar groups are radially anisotropic. Interestingly, N-rich, Fe-rich stars exhibit different rotation patterns than N-poor stars with similar metallicities. The stellar populations with different nitrogen of M 22 exhibit similar rotation patterns and isotropic motions. We discuss these findings in the context of the formation of multiple populations.
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The internal dynamics of multiple stellar populations in Globular Clusters (GCs) provides unique constraints on the physical processes responsible for their formation. Specifically, the present-day kinematics of cluster stars, such as rotation and ve
locity dispersion, seems to be related to the initial configuration of the system. In recent work (Milone et al. 2018), we analyzed for the first time the kinematics of the different stellar populations in NGC0104 (47Tucanae) over a large field of view, exploiting the Gaia Data Release 2 proper motions combined with multi-band ground-based photometry. In this paper, based on the work by Cordoni et al. (2019), we extend this analysis to six GCs, namely NGC0288, NGC5904 (M5), NGC6121 (M4), NGC6752, NGC6838 (M71) and further explore NGC0104. Among the analyzed clusters only NGC0104 and NGC5904 show significant rotation on the plane of the sky. Interestingly, multiple stellar populations in NGC5904 exhibit different rotation curves.
The internal dynamics of multiple stellar populations in Globular Clusters (GCs) provides unique constraints on the physical processes responsible for their formation. Specifically, the present-day kinematics of cluster stars, such as rotation and ve
locity-dispersion, could be related to the initial configuration of the system. In recent work, we provided the first study of the kinematics of different stellar populations in NGC$,$0104 over a large field of view in the plane of the sky, exploiting Gaia Data Release 2 (DR2) proper motions combined with multi-band ground-based photometry. In this paper, we combine Gaia DR2 proper motions with Very Large Telescope radial velocities to investigate the kinematics along the line of sight and in the plane of the sky of multiple populations in seven GCs, namely NGC$,$0104, NGC$,$0288, NGC$,$5904, NGC$,$6121, NGC$,$6254, NGC$,$6752 and NGC$,$6838. Among the analyzed clusters only NGC$,$0104 and NGC$,$5904 show significant rotation. Separating our sample into two groups of first- and second-population stars (1P and 2P) we find that overall these two populations exhibit a similar rotation pattern in NGC$,$0104. However, some hints of different rotation are observed in the external regions of this cluster. Interestingly, 1P and 2P stars in NGC$,$5904 show different rotation curves, with distinct phases and such difference is significant at the $sim$2.5-$sigma$ level. The analysis of the velocity-dispersion profiles of multiple populations confirms that 2P stars of NGC$,$0104 show stronger anisotropy than the 1P.
Historically, photometry has been largely used to identify stellar populations (MPs) in Globular Clusters (GCs) by using diagrams that are based on colours and magnitudes that are mostly sensitive to stars with different metallicities or different ab
undances of helium, carbon, nitrogen and oxygen. In particular, the pseudo two-colour diagram called chromosome map (ChM), allowed the identification and the characterization of MPs in about 70 GCs by using appropriate filters of the Hubble Space Telescope (HST) that are sensitive to the stellar content of He, C, N, O and Fe. We use here high-precision HST photometry from F275W, F280N, F343N, F373N, and F814W images of Omega Centauri to investigate its MPs. We introduce a new ChM whose abscissa and ordinate are mostly sensitive to stellar populations with different magnesium and nitrogen, respectively, in monometallic GCs. This ChM is effective in disentangling the MPs based on their Mg chemical abundances, allowing us to explore, for the first time, possible relations between the production of these elemental species for large samples of stars in GCs. By comparing the colours of the distinct stellar populations with the colours obtained from appropriate synthetic spectra we provide photometric-like estimates of the chemical composition of each population. Our results show that, in addition to first generation (1G) stars, the metal-poor population of Omega Centauri hosts four groups of second-generation stars with different [N/Fe], namely, 2GA--D. 2GA stars share nearly the same [Mg/Fe] as the 1G, whereas 2GB, 2GC and 2GD stars are Mg depleted by ~0.15, ~0.25 and ~0.45 dex, respectively. We provide evidence that the metal-intermediate populations host stars with depleted [Mg/Fe].
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