Evolution of long-lived globular cluster stars

Chantereau, William; Charbonnel, C.; Decressin, T.

doi:10.1051/0004-6361/201525929

Cited by 32 publications

(64 citation statements)

References 77 publications

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“…The implication of initial helium enhancement on the HB morphology has been extensively discussed in the literature (e.g. D 'Antona et al 2010;Chantereau et al 2015, and references therein). Helium variations are also invoked to explain (at least partly) the peculiar photometric patterns (multiple sequences and/or spreads at the turnoff and/or along the subgiant and giant branches) in the colour−magnitude diagram (CMD) of several GCs Marino et al 2012;Piotto et al 2012;Monelli et al 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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Section: Introductionmentioning

confidence: 99%

Evolution of long-lived globular cluster stars

Charbonnel

Chantereau

2016

A&A

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“…These sequences are provided for two progenitor metallicities Z=0.001 and Z=0.0005. To date, no such exploration of the evolution of He-rich stars exists in the literature, the only exception is that of Chantereau et al (2015), who presented evolutionary sequences for He-rich progenitors for low-mass stars (up to 1 M ⊙ ) with Z=0.0005 from the ZAMS to the end of the AGB phase, but did not compute the white dwarf stage. We emphasize that the comptutation of the entire evolutionary history of progenitor stars allows us to have self-consistent white dwarf initial models.…”

Section: Introductionmentioning

confidence: 99%

The evolution of white dwarfs resulting from helium-enhanced, low-metallicity progenitor stars

Althaus

Gerónimo

Córsico

et al. 2017

A&A

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Context. Some globular clusters host multiple stellar populations with different chemical abundance patterns. This is particularly true for ω Centauri, which shows clear evidence of a helium-enriched sub-population characterized by a helium abundance as high as Y = 0.4 Aims. We present a whole and consistent set of evolutionary tracks from the ZAMS to the white dwarf stage appropriate for the study of the formation and evolution of white dwarfs resulting from the evolution of helium-rich progenitors. Methods. White dwarf sequences have been derived from progenitors with stellar mass ranging from 0.60 to 2.0 M ⊙ and for an initial helium abundance of Y = 0.4. Two values of metallicity have been adopted: Z = 0.001 and Z = 0.0005. Results. Different issues of the white dwarf evolution and their helium-rich progenitors have been explored. In particular, the final mass of the remnants, the role of overshooting during the thermally-pulsing phase, and the cooling of the resulting white dwarfs differ markedly from the evolutionary predictions of progenitor stars with standard initial helium abundance. Finally, the pulsational properties of the resulting white dwarfs are also explored. Conclusions. We find that, for the range of initial masses explored in this paper, the final mass of the helium-rich progenitors is markedly larger than the final mass expected from progenitors with the usual helium abundance. We also find that progenitors with initial mass smaller than M ⋆ ≃ 0.65 M ⊙ evolve directly into helium-core white dwarfs in less than 14 Gyr, and that for larger progenitor masses the evolution of the resulting low-mass carbon-oxygen white dwarfs is dominated by residual nuclear burning. For helium-core white dwarfs, we find that they evolve markedly faster than their counterparts coming from standard progenitors. Also, in contrast with what occurs for white dwarfs resulting from progenitors with the standard helium abundance, the impact of residual burning on the cooling time of white dwarfs is not affected by the occurrence of overshooting during the thermally-pulsing phase of progenitor stars.

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“…While the FRMS scenario predicts that 2P stars can start their life with an helium mass fraction of between that of 1P stars (i.e., typically 0.248 for the metallicity presented in this study) and 0.8, the maximum helium enrichment provided by the AGB scenario amounts to at most ∼0.36−0.38 in mass fraction (e.g., Siess 2010;Doherty et al 2014). Since the initial helium content is an important ingredient for the evolution of stars (e.g., Iben & Rood 1969;Demarque et al 1971;Sweigart 1978;Maeder 2009;Chantereau et al 2015), it is mandatory to quantify the effect of these differences on the expected properties of GC multiple populations (e.g., D'Antona et al 2002;Salaris et al 2006;Pietrinferni et al 2009;Sbordone et al 2011;Valcarce et al 2012;Cassisi et al 2013a).…”

Section: Introductionmentioning

confidence: 99%

“…However, the exact processes governing the formation of multiple populations in GCs are far from being understood and are strongly debated (e.g., Bastian & Lardo 2015;Renzini et al 2015;Krause et al 2016). Competing scenarios invoke different types of possible 1P polluters, namely asymptotic giant branch stars (AGB; Ventura et al 2001;D'Ercole et al 2010;Ventura & D'Antona 2011;Ventura et al 2013), fast-rotating massive stars (FRMS; Prantzos & Charbonnel 2006;Decressin et al 2007a,b;Krause et al 2013;Chantereau et al 2015), massive binary stars (de Mink et al 2009), supermassive stars (Denissenkov & Hartwick 2014), or a combination of some of the above-mentioned polluters (Sills & Glebbeek 2010;Bastian et al 2013).…”

Section: Introductionmentioning

confidence: 99%

“…The files containing the relevant evolution characteristics of the complete grid of models from the pre-main sequence up to the end of the stellar life (see Appendix of Chantereau et al 2015) are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/592/A111 As in Chantereau et al (2015), we also provide all the tables on the website http: //obswww.unige.ch/Recherche/evol/starevol/Globular.php High-resolution photometry reveals a wide variety of features in different areas of the color-magnitude diagram (CMD) of many GCs that are not consistent with single stellar populations (see, e.g., the review of Piotto 2009). Depending on the cluster, wide or multiple main sequences are observed (MS, Milone et al 2012b,c;King et al 2012), multiple subgiant branches (SGB, Anderson et al 2009;Milone et al 2009;Moretti et al 2009), distinct red giant branches (RGB, Han et al 2009;Roh et al 2011;Monelli et al 2013), or extended horizontal branches (HB, e.g., Momany et al 2004;Busso et al 2007;Dalessandro et al 2011).…”

Section: Introductionmentioning

confidence: 99%

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Evolution of long-lived globular cluster stars

Chantereau

Charbonnel

Meynet

2016

A&A

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Context. Globular clusters host multiple populations of long-lived low-mass stars whose origin remains an open question. Several scenarios have been proposed to explain the associated photometric and spectroscopic peculiarities. They differ, for instance, in the maximum helium enrichment they predict for stars of the second population, which these stars can inherit at birth as the result of the internal pollution of the cluster by different types of stars of the first population. Aims. We present the distribution of helium-rich stars in present-day globular clusters as it is expected in the original framework of the fast-rotating massive stars scenario (FRMS) as first-population polluters. We focus on NGC 6752. Methods. We completed a grid of 330 stellar evolution models for globular cluster low-mass stars computed with different initial chemical compositions corresponding to the predictions of the original FRMS scenario for [Fe/H] = −1.75. Starting from the initial helium-sodium relation that allows reproducing the currently observed distribution of sodium in NGC 6752, we deduce the helium distribution expected in that cluster at ages equal to 9 and 13 Gyr. We distinguish the stars that are moderately enriched in helium from those that are very helium-rich (initial helium mass fraction below and above 0.4, respectively), and compare the predictions of the FRMS framework with other scenarios for globular cluster enrichment. Results. The effect of helium enrichment on the stellar lifetime and evolution reduces the total number of very helium-rich stars that remain in the cluster at 9 and 13 Gyr to only 12% and 10%, respectively, from an initial fraction of 21%. Within this age range, most of the stars still burn their hydrogen in their core, which widens the MS band significantly in effective temperature. The fraction of very helium-rich stars drops in the more advanced evolution phases, where the associated spread in effective temperature strongly decreases. These stars even disappear from the horizontal branch and the asymptotic giant branch at 13 Gyr. Conclusions. The helium constraint is no suitable criterion for clearly distinguishing between the scenarios for GC self-enrichment because only few very helium-rich stars are predicted in the investigated framework and because it is difficult to derive the helium content of GC stars observationally. However, the helium constraint indicates some difficulties of the original FRMS scenario that require the exploration of alternatives.

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Evolution of long-lived globular cluster stars

Cited by 32 publications

References 77 publications

Evolution of long-lived globular cluster stars

Evolution of long-lived globular cluster stars

The evolution of white dwarfs resulting from helium-enhanced, low-metallicity progenitor stars

Evolution of long-lived globular cluster stars

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