Multiple populations in massive star clusters under the magnifying glass of photometry: theory and tools

Cassisi, S.; Salaris, Maurizio

doi:10.1007/s00159-020-00127-y

Cited by 30 publications

(10 citation statements)

References 124 publications

(173 reference statements)

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“…The ubiquitous nature of the multiple populations (MPs) in globular clusters (GCs) is an enigmatic phenomenon that cannot be easily understood in modern astrophysics (e.g., see Bastian & Lardo 2018;Gratton et al 2019;Cassisi & Salaris 2020). Once thought to be simple groups of old stars, not only the Galactic but also the extragalactic GCs show MPs containing at least two populations: One is called first generation (FG) with chemical compositions similar to abundance patterns observed in Galactic field stars with the same metallicity, while the other is called a second generation (SG) showing the chemical compositions that experienced proton capture processes at high temperature.…”

Section: Introductionmentioning

confidence: 99%

Multiple Stellar Populations of Globular Clusters from Homogeneous Ca–CN–CH–NH Photometry. VII. Metal-poor Populations in 47 Tucanae (NGC 104)* †

Lee¹

2022

ApJS

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We present new large field-of-view (∼1°×1°) Ca-CN photometry of the prototypical metal-rich globular cluster 47 Tucanae (NGC 104). Our results are the following. (1) The populational number ratios of the red giant branch (RGB) and red horizontal branch (RHB) are in excellent agreement: n(CN-w):n(CN-s) = 30:70 (±1–2), where the CN-w and CN-s stand for the CN-weak and CN-strong populations, respectively. Both the CN-s RGB and RHB populations are more centrally concentrated than those of CN-w populations are. (2) Our photometric metallicities of individual RGB stars in each population can be well described by bimodal distributions with two metallicity peaks, [Fe/H] ∼−0.72 and −0.92 dex, where the metal-poor components occupy ∼13% of the total RGB stars. The metal-poor populations are more significantly centrally concentrated than the metal-rich populations, showing a similar result that we found in M3. (3) The RGB bump V magnitudes of individual populations indicate that there is no difference in the helium abundance between the two metal-poor populations, while the helium enhancement of ΔY ∼0.02–0.03 is required between the the two metal-rich populations. (4) The RHB morphology of 47 Tuc appears to support our idea of the bimodal metallicity distribution of the cluster. We suggest that 47 Tuc could be another example of merger remnants of two globular clusters, similar to M3 and M22.

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Section: Introductionmentioning

confidence: 99%

Multiple Stellar Populations of Globular Clusters from Homogeneous Ca–CN–CH–NH Photometry. VII. Metal-poor Populations in 47 Tucanae (NGC 104)* †

Lee¹

2022

ApJS

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“…As of now, we do not properly understand the origin of multiple stellar populations in GCs. In recent years, various excellent reviews have been dedicated to GCs and their stellar populations (e.g., [6][7][8][9]36,37]). Here, we discuss the state of the art of observed properties of multiple stellar populations in GCs by focusing on recent results, largely based on photometry.…”

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confidence: 99%

Multiple Populations in Star Clusters

Milone

Marino

2022

Universe

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We review the multiple population (MP) phenomenon of globular clusters (GCs): i.e., the evidence that GCs typically host groups of stars with different elemental abundances and/or distinct sequences in photometric diagrams. Most Galactic and extragalactic clusters exhibit internal variations of He, C, N, O, Na, and Al. They host two distinct stellar populations: the first population of stars, which resemble field stars with similar metallicities, and one or more second stellar populations that show the signature of high-temperature H-burning. In addition, a sub-sample of clusters hosts stellar populations with different heavy-element abundances. The MP origin remains one of the most puzzling, open issues of stellar astrophysics. We summarize the scenarios for the MP formation and depict the modern picture of GCs and their stellar populations along with the main evolutionary phases. We show that the MP behavior dramatically changes from one cluster to another and investigate their complexity to define common properties. We investigate relations with the host galaxy, the parameters of the host clusters (e.g., GC’s mass, age, orbit), and stellar mass. We summarize results on spatial distribution and internal kinematics of MPs. Finally, we review the relation between MPs and the so-called second-parameter problem of the horizontal-branch morphology of GCs and summarize the main findings on the extended main sequence phenomenon in young clusters.

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“…However, globular clusters are complex systems that host multiple stellar populations. This has been shown both with spectroscopy, with the detection of star-to-star abundance variation [1,2], and with photometry, with the detection of separated sequences in the subgiant and red giant branches in the color magnitude diagram of several clusters [3,4]. Such signatures have been attributed to multiple episodes of star formation.…”

Section: Introductionmentioning

confidence: 81%

“…A few other alternative scenarios have also been proposed [2]. However, it seems that so far all of the proposed scenarios face problems to reproduce key observational facts regarding globular clusters [2,19,4].…”

Section: Introductionmentioning

confidence: 99%

“…Spallation in this material can happen only due to the Galactic cosmic-ray flux, as in principle there is no local source able to accelerate particles to cosmic-ray-like energies. The ejecta would be exposed to cosmic-rays for a time scale that is too short to produce Be abundance at the level found in the ISM, particularly given that second generation stars have about the same C+N+O abundances of first generation stars [4].…”

Section: Introductionmentioning

confidence: 99%

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Beryllium abundances in turn-off stars of globular clusters with the CUBES spectrograph

Giribaldi,

Smiljanic

2022

Preprint

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Globular clusters host multiple stellar populations that display star-to-star variation of light elements that are affected by hot hydrogen burning (e.g., He, C, N, O). Several scenarios have been suggested to explain these variations. Most involve multiple star formation episodes, where later generations are born from material contaminated by the nucleosynthetic products of the previous stellar generation(s). One difficulty in the modelling of such scenarios is knowing the extent to which processed and pristine material are mixed. In this context, beryllium abundances measured in turn-off stars of different generations can provide new information. Beryllium originates from cosmic-ray spallation and can only be destroyed inside stars. Beryllium abundances can thus directly measure the degree of pollution of the material that formed stars in globular clusters. Turn-off stars in globular clusters are however faint and such studies are beyond the capabilities of current instrumentation. In this work, we show the progress that the CUBES spectrograph will bring to this area. Our simulations indicate that CUBES will enable the detection of variations of about 0.6 dex in the Be abundances between stars from different generations, in several nearby globular clusters with turn-off magnitude down to V = 18 mag.

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Multiple populations in massive star clusters under the magnifying glass of photometry: theory and tools

Abstract: The version presented here may differ from the published version or from the version of the record. Please see the repository URL above for details on accessing the published version and note that access may require a subscription.

Cited by 30 publications

References 124 publications

Multiple Stellar Populations of Globular Clusters from Homogeneous Ca–CN–CH–NH Photometry. VII. Metal-poor Populations in 47 Tucanae (NGC 104)* †

Multiple Stellar Populations of Globular Clusters from Homogeneous Ca–CN–CH–NH Photometry. VII. Metal-poor Populations in 47 Tucanae (NGC 104)* †

Multiple Populations in Star Clusters

Beryllium abundances in turn-off stars of globular clusters with the CUBES spectrograph

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