Li in NGC 6752 and the formation of globular clusters

Pasquini, L.; Bonifacio, P.; Molaro, P.; François, P.; Spite, F.; Gratton, R.; Carretta, E.; Wolff, B.

doi:10.1051/0004-6361:20053607

Cited by 118 publications

(181 citation statements)

References 25 publications

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“…The cluster stars display a very mild Li-Na anticorrelation. Compared to NGC 6752, in which a spread of 0.6 dex in [Na/Fe] corresponds to a spread of 0.6 dex in A(Li) (Pasquini et al 2005), the anti-correlation in M 4 is hardly detectable, with a spread of 0.1 dex in A(Li) corresponding to a spread of 0.6 dex in A(Na). The sample has, however, a Spearman rank correlation coefficient of C S = −0.34, corresponding to a probability of 0.002 that the observed correlation is, in fact, spurious.…”

Section: Discussionmentioning

confidence: 68%

Lithium and sodium in the globular cluster M 4

Monaco

Villanova

Bonifacio

et al. 2012

A&A

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Context. The abundance inhomogeneities of light elements observed in globular clusters (GCs), and notably the ubiquitous Na-O anti-correlation, are generally interpreted as evidence that GCs comprise several generations of stars. There is an on-going debate as to the nature of the stars, which produce the inhomogeneous elements, and investigating the behavior of several elements is a way to shed new light on this problem. Aims. We aim at investigating the Li and Na content of the GC M 4, that is known to have a well defined Na-O anti-correlation. Methods. We obtained moderate resolution (R = 17 000-18 700) spectra for 91 main sequence (MS)/sub-giant branch stars of M 4 with the Giraffe spectrograph at the FLAMES/VLT ESO facility. Using model atmospheres analysis we measured lithium and sodium abundances. Results. We detect a weak Li-Na anti-correlation among un-evolved MS stars. One star in the sample, # 37934, shows the remarkably high lithium abundance A(Li) = 2.87, compatible with current estimates of the primordial lithium abundance. Conclusions. The shallow slope found for the Li-Na anti-correlation suggests that lithium is produced in parallel to sodium. This evidence, coupled with its sodium-rich nature, suggests that the high lithium abundance of star # 37934 may originate by pollution from a previous generations of stars. The recent detection of a Li-rich dwarf of pollution origin in the globular cluster NGC 6397 may also point in this direction. Still, no clear cut evidence is available against a possible preservation of the primordial lithium abundance for star # 37934.

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Section: Discussionmentioning

confidence: 68%

Lithium and sodium in the globular cluster M 4

Monaco

Villanova

Bonifacio

et al. 2012

A&A

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133

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“…They are also the only two clusters where an Na-Li anticorrelation has also been observed (Pasquini et al 2005;Bonifacio et al 2007). …”

Section: Introductionmentioning

confidence: 89%

Sulfur in the globular clusters 47 Tucanae and NGC 6752

Sbordone

Limongi

Chieffi

et al. 2009

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Context. The light elements Li, O, Na, Al, and Mg are known to show star-to-star variations in the globular clusters 47 Tuc and NGC 6752. Such variations are interpreted as coming from processing in a previous generation of stars. Aims. In this paper we investigate the abundances of the α-element sulfur, for which no previous measurements exist. In fact this element has not been investigated in any Galactic globular cluster so far. The only globular cluster for which such measurements are available is Terzan 7, which belongs to the Sgr dSph.Methods. We use high-resolution spectra of the S i Mult. 1, acquired with the UVES spectrograph at the 8.2 m VLT-Kueyen telescope, for turn-off and giant stars in the two globular clusters. The spectra were analysed making use of ATLAS static plane parallel model atmospheres and SYNTHE spectrum synthesis. We also compute 3D corrections from CO 5 BOLD hydrodynamic models and apply corrections due to NLTE effects taken from the literature. Results. In the cluster NGC 6752 sulfur has been measured only in four subgiant stars. We find no significant star-to-star scatter and a mean [S/Fe] = +0.49 ± 0.15, consistent with what is observed in field stars of the same metallicity. In the cluster 47 Tuc we measured S in 4 turn-off and 5 subgiant stars with a mean [S/Fe] = +0.18 ± 0.14. While this result is compatible with no star-to-star scatter we notice a statistically significant correlation of the sulfur abundance with the sodium abundance and a tentative correlation with the silicon abundance. Conclusions. The sulfur-sodium correlation is not easily explained in terms of nucleosynthesis. An origin due to atomic diffusion can be easily dismissed. The correlation cannot be easily dismissed either, in view of its statistical significance, until better data for more stars is available.

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“…-The dilution factor a t varies during the lifetime of individual 1P polluters between 0.99 (ejecta strongly diluted with the surrounding intra-cluster gas) and a minimum value a min of 0.2 that is constrained by the Na-Li anti-correlation observed in NGC 6752 turn-off stars (observations by Pasquini et al 2005; see, e.g., Decressin et al 2007b). …”

Section: P Modelsmentioning

confidence: 99%

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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Li in NGC 6752 and the formation of globular clusters

Cited by 118 publications

References 25 publications

Lithium and sodium in the globular cluster M 4

Lithium and sodium in the globular cluster M 4

Sulfur in the globular clusters 47 Tucanae and NGC 6752

Evolution of long-lived globular cluster stars

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