The lithium content of<i>ω</i> Centauri

Monaco, L.; Bonifacio, P.; Sbordone, L.; Villanova, S.; Pancino, E.

doi:10.1051/0004-6361/201015162

Cited by 51 publications

(66 citation statements)

References 48 publications

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“…The two temperature scales are in excellent agreement, with a mean difference of −6 ± 5 K (σ Δ(T eff ) = 60 K). The accuracy of the T eff determination using H α line fitting is usually, however, of the order of ∼150 K and is dominated by uncertainties in the continuum normalization and/or in the correction of the blaze function of the spectrograph (Bonifacio et al 2007;Sbordone et al 2010;Monaco et al 2010). In the following we will adopt 150 K as uncertainty on the T eff determination.…”

Section: Abundance Analysismentioning

confidence: 99%

“…It is interesting in this context that all of the GCs studied so far (ω Cen, NGC 6752, NGC 6397, 47 Tuc, M 4, see Monaco et al 2010;Mucciarelli et al 2011, and references therein), present -at least in their FG of stars -a Li content comparable to that of warm metal-poor halo dwarfs, i.e. the socalled Spite plateau (Spite & Spite 1982;Sbordone et al 2010).…”

Section: Introductionmentioning

confidence: 96%

“…The simplest interpretation of the Spite plateau is that the lithium observed in these old stars is the lithium produced during the Big Bang (Iocco et al 2009). If this is the case, however, there is a "cosmological lithium problem", because the level of the Spite plateau is a factor of three to five lower than the primordial lithium predicted by Standard Big Bang Nucleosynthesis and the baryonic density measured from the fluctuations of the Cosmic Microwave Background (see, e.g., Monaco et al 2010;Sbordone et al 2010, and references therein).…”

Section: Introductionmentioning

confidence: 99%

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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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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: Abundance Analysismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

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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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“…Clearly, the chemical evolution of Li is far from being straightforward, as the remarkably constant Li abundance with metallicity observed by Monaco et al (2010) in ω Cen also shows. In addition, it is important to bear in mind that it is not straightforward to interpret Li abundance observations, given the many ill-constrained physical mechanisms that may play a relevant role in defining surface Li abundances in present-day stars (e.g., Mucciarelli et al 2011b).…”

Section: The Case Of Ngc 2808mentioning

confidence: 99%

Formation of multiple populations in globular clusters: another possible scenario

Valcarce

Catelan

2011

A&A

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Aims. While spreads in chemical composition are now believed to be a universal characteristic of globular clusters (GCs), not all of them display evidence of multiple populations in their color-magnitude diagrams (CMDs). Here we present a new scenario for the formation of GCs, in an attempt to qualitatively explain these otherwise elusive observational results. Methods. Our scenario divides GCs into three groups, depending on the initial mass (M I ) of the progenitor structure (PS), as follows: i) massive PSs can retain the gas ejected by massive stars, including the ejecta of core-collapse SNe. ii) Intermediate-mass PSs can retain at least a fraction of the fast winds of massive stars, but none of the core-collapse SNe ejecta. iii) Low-mass PSs can only retain the slow winds of intermediate-mass stars. The first group would contain members such as ω Centauri (NGC 5139), M 54 (NGC 6715), M 22 (NGC 6656), and Terzan 5, whereas NGC 2808 (and possibly NGC 2419) would be members of the second group. The remaining GCs that have only a spread in light elements, such as O and Na, would be members of the third group. Results. According to our scenario, the different components of ω Cen should not have a sizeable spread in age. We argue that this is consistent with the available observations. We present other simple arguments in favor of our scenario, which can be described in terms of two main analytical relations: i) one between the actual observed ratio of the number of first to second generation stars (R FG SG ) and the fraction of first generation stars that have been lost by the GC (S L ) and ii) another between S L and M I . We also suggest a series of future improvements to and empirical tests of the modeling that may help decide whether the proposed scenario properly describes the chemical evolution of GCs.

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“…After the pioneering works with 4 m class telescopes (Pasquini & Molaro 1996, 1997Castilho et al 2000), the study of Li in globular clusters (GC) has received a tremendous boost with 8 m telescopes (Boesgaard et al 1998;Thévenin et al 2001;Bonifacio et al 2002Bonifacio et al , 2007Pasquini et al 2004), and, with the advent of multi object spectrographs, many un-evolved and evolved stars have been observed for Li in the nearest GCs (Korn et al 2007;Lind et al 2009;D'Orazi & Marino 2010;Monaco et al 2010).…”

Section: Introductionmentioning

confidence: 99%

Li – O anti-correlation in NGC 6752: evidence for Li-enriched polluting gas

Shen

Bonifacio

Pasquini

et al. 2010

A&A

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Context. Elemental correlations and anti-correlations are known to be present in globular clusters (GCs) owing to pollution by CNO cycled gas. Because of its fragility Li is destroyed at the temperature at which the CNO cycling occurs, and this makes Li a crucial study for the nature of the contaminating stars. Aims. We observed 112 un-evolved stars at the Turnoff of the NGC 6752 cluster with FLAMES at the VLT to investigate the presence and the extent of a Li-O correlation. This correlation is expected if there is a simple pollution scenario. Methods. Li (670.8 nm) and O triplet (771 nm) abundances are derived in NLTE. All stars belong to a very narrow region of the color-magnitude diagram, so they have similar stellar parameters (T eff , log g). Results. We find that O and Li correlate, with a high statistical significance that confirms the early results for this cluster. At first glance this is what is expected if a simple pollution of pristine gas with CNO cycled gas (O-poor, Li-poor) occurred. The slope of the relationship, however, is about 0.4, and differs from unity by over 7σ. A slope of one is the value predicted for a pure contamination model. Conclusions. We confirm an extended Li-O correlation in non evolved stars of NGC 6752. At the same time the characteristic of the correlation shows that a simple pollution scenario is not sufficient to explain the observations. Within this scenario the contaminant gas must have been enriched in Li. This would rule out massive stars as main polluters, and favor the hypothesis that the polluting gas was enriched by intermediate or high-mass AGB stars, unless the former can be shown to be able to produce Li. According to our observations, the fraction of polluting gas contained in the stars observed is a considerable fraction of the stellar mass of the cluster.

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The lithium content ofω Centauri

Cited by 51 publications

References 48 publications

Lithium and sodium in the globular cluster M 4

Lithium and sodium in the globular cluster M 4

Formation of multiple populations in globular clusters: another possible scenario

Li – O anti-correlation in NGC 6752: evidence for Li-enriched polluting gas

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