Are there any first-generation stars in globular clusters today?

Charbonnel, C.; Chantereau, William; Krause, Martin; Primas, F.; Wang, Yue

doi:10.1051/0004-6361/201424804

Cited by 29 publications

(44 citation statements)

References 43 publications

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“…This grid of models has been successfully used to explain the lack of Na-rich AGB stars in the GC NGC 6752 (Charbonnel et al 2014). Other aspects related to the properties of stellar populations in GCs and of the GC CMDs at various phases of their evolution will be investigated in forthcoming papers in this series.…”

Section: Discussionmentioning

confidence: 99%

“…As FRMS release the first material of original GC composition at the very beginning of their evolution, and later material richer in H-burning ashes, one expects 2P stars with Na and He contents similar to that of 1P stars to form first, and then 2P stars with various degrees of Na and He enrichment (see, e.g., Charbonnel et al 2014).…”

Section: P Modelsmentioning

confidence: 99%

“…It was also proposed that the ejecta of FRMS and/or high-mass interacting binaries were actually accreted by low-mass pre-main sequence stars of the same generation (Bastian et al 2013b; see also Scenario II of Prantzos & Charbonnel 2006) 3 , in which case the concept of distinct stellar generations is also misleading. Last but not least, in the FRMS polluter model a large percentage of (if not all) the stars exhibiting low sodium abundance (and that are therefore counted as 1G members; see Prantzos & Charbonnel 2006;Carretta et al 2009b) could have formed from pristine material mixed with the H-burning ashes of the fast-evolving 1G polluters (Charbonnel et al 2014); in this case GCs would be formally devoid of 1G low-mass stars, their hosts being actually secondary star formation products with chemical properties spanning the whole range of the observed O-Na anti-correlations.…”

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confidence: 99%

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Evolution of long-lived globular cluster stars

Chantereau

Charbonnel

Decressin

2015

A&A

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Context. Our understanding of the formation and early evolution of globular clusters (GCs) has been totally overthrown with the discovery of the peculiar chemical properties of their long-lived host stars. Aims. As a consequence, the interpretation of the observed color-magnitude diagrams and of the properties of the GC stellar populations requires the use of stellar models computed with relevant chemical compositions.Methods. We present a grid of 224 stellar evolution models for low-mass stars with initial masses between 0.3 and 1.0 M and initial helium mass fraction between 0.248 and 0.8 computed for [Fe/H] = -1.75 with the stellar evolution code STAREVOL. This grid is made available to the community. Results. We explore the implications of the assumed initial chemical distribution for the main properties of the stellar models: evolution paths in the Hertzsprung-Russel diagram (HRD), duration and characteristics of the main evolutionary phases, and the chemical nature of the white dwarf remnants. We also provide the ranges in initial stellar mass and helium content of the stars that populate the different regions of the HRD at the ages of 10 and 13.4 Gyr, which are typical for Galactic GCs.

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Section: Discussionmentioning

confidence: 99%

Section: P Modelsmentioning

confidence: 99%

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confidence: 99%

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Evolution of long-lived globular cluster stars

Chantereau

Charbonnel

Decressin

2015

A&A

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“…expulsion, or because at least all the strongly gravitationally bound gas is converted into stars (Charbonnel et al 2014). The second assumption is that a GC formed sometime within the first two Gyrs after the Big-Bang, corresponding to z > 3 or ∆T epoch 2 Gyr.…”

Section: The Chance To Observe a Forming Gcmentioning

confidence: 99%

Paving the way for the JWST: witnessing globular cluster formation at z > 3

Vanzella¹,

Calura²,

Meneghetti³

et al. 2017

Monthly Notices of the Royal Astronomical Society

178

215

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We report on five compact, extremely young (< 10 Myr) and blue (β U V < −2.5, F λ = λ β ) objects observed with VLT/MUSE at redshift 3.1169, 3.235, in addition to three objects at z = 6.145. These sources are magnified by the Hubble Frontier Field galaxy clusters MACS J0416 and AS1063. Their de-lensed half light radii (R e ) are between 16 to 140 pc, the stellar masses are 1 − 20 × 10 6 M , the magnitudes are m U V = 28.8 − 31.4 (−17 < M U V < −15) and specific star formation rates can be as large as ∼ 800 Gyr −1 . Multiple images of these systems are widely separated in the sky (up to 50 ) and individually magnified by factors 3-40. Remarkably, the inferred physical properties of two objects are similar to those expected in some globular cluster formation scenarios, representing the best candidate proto-globular clusters (proto-GC) discovered so far. Rest-frame optical high dispersion spectroscopy of one of them at z = 3.1169 yields a velocity dispersion σ v 20 km s −1 , implying a dynamical mass dominated by the stellar mass. Another object at z = 6.145, with de-lensed31.4), shows a stellar mass and a star-formation rate surface density consistent with the values expected from popular GC formation scenarios. An additional star-forming region at z = 6.145, with de-lensed m U V 32, a stellar mass of 0.5 ×10 6 M and a star formation rate of 0.06 M yr −1 is also identified. These objects currently represent the faintest spectroscopically confirmed star-forming systems at z > 3, elusive even in the deepest blank fields. We discuss how proto-GCs might contribute to the ionization budget of the universe and augment Lyα visibility during reionization. This work underlines the crucial role of JWST in characterizing the restframe optical and near-infrared properties of such low-luminosity high−z objects.

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“…Norris 2004; Prantzos & Charbonnel 2006;Carretta et al 2010;Schaerer & Charbonnel 2011). However, Charbonnel et al (2014) propose one variation of the FRMS scenario where only massive stars form from pure original proto-cluster material, and all low-mass GC stars form from a mixture between H-processed stellar ejecta and protocluster material in variable proportions accounting for both the observed Li-Na anti-correlation (e.g. Lind et al 2009) and the typical percentage of low-sodium stars that are usually classified as 1P stars (∼30%; Prantzos & Charbonnel 2006;Carretta et al 2009b;Carretta 2013).…”

Section: Introductionmentioning

confidence: 99%

Evolution of long-lived globular cluster stars

Charbonnel

Chantereau

2016

A&A

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Context. Long-lived stars in globular clusters exhibit chemical peculiarities with respect to their halo counterparts. In particular, sodium-enriched stars are identified as belonging to a second stellar population born from cluster material contaminated by the hydrogen-burning ashes of a first stellar population. Their presence and numbers in different locations of the colour-magnitude diagram provide important constraints on the self-enrichment scenarios. In particular, the ratio of Na-poor to Na-rich stars on the asymptotic giant branch (AGB) has recently been found to vary strongly from cluster to cluster (NGC 6752, 47 Tuc, and NGC 2808), while it is relatively constant on the red giant branch (RGB). Aims. We investigate the impact of both age and metallicity on the theoretical sodium spread along the AGB within the framework of the fast rotating massive star (FRMS) scenario for globular cluster self-enrichment. Methods. We computed evolution models of low-mass stars for four different metallicities ([Fe/H] = −2.2, −1.75, −1.15, −0.5) assuming the initial helium-sodium abundance correlation for second population stars derived from the FRMS models and using mass loss prescriptions on the RGB with two realistic values of the free parameter in the Reimers formula. Results. Based on this grid of models we derive the theoretical critical initial mass for a star born with a given helium, sodium, and metal content that determines whether that star will climb or not the AGB. This allows us to predict the maximum sodium content expected on the AGB for globular clusters as a function of both their metallicity and age. We find that (1) at a given metallicity, younger clusters are expected to host AGB stars exhibiting a larger sodium spread than older clusters and (2) at a given age, higher sodium dispersion along the AGB is predicted in the most metal-poor globular clusters than in the metal-rich ones. We also confirm the strong impact of the mass loss rate in the earlier evolution phases on the Na cut on the AGB: the higher the mass loss, the stronger the trends with age and metallicity. Conclusions. The theoretical trends we obtain provide, in principle, an elegant qualitative explanation to the different sodium spreads that are observed along the AGB in the Galactic globular clusters of different ages and [Fe/H] values. Although it is real, the slope with both age and metallicity is relatively flat, although it steepens when accounting for mass loss variations. Therefore, additional parameters may play a role in inducing cluster to cluster variations, that are difficult to disentangle from existing data.

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Are there any first-generation stars in globular clusters today?

Cited by 29 publications

References 43 publications

Evolution of long-lived globular cluster stars

Evolution of long-lived globular cluster stars

Paving the way for the JWST: witnessing globular cluster formation at z > 3

Evolution of long-lived globular cluster stars

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