Bimodality of light and s-elements in M4 (NGC 6121)

Villanova, S.; Geisler, Doug

doi:10.1051/0004-6361/201117552

Cited by 68 publications

(80 citation statements)

References 40 publications

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“…The observations of the simultaneous, significant variation in the Na content might pose a problem to the viability of such models for M 4. Notice, however, that the recent results by Villanova & Geisler (2011) support FRMS as likely polluters from which the second generation of stars formed in M 4 (see also Yong et al 2008;Lind et al 2011). Figure 2 shows another remarkable fact: there is one star, # 37934, that displays a lithium abundance, which is significantly higher than that of the others.…”

Section: Discussionmentioning

confidence: 76%

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: Discussionmentioning

confidence: 76%

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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“…This is a small value, comparable with the typical measurement error of any chemical abundance determination procedure (e.g., Villanova et al 2011), so we can assume that any intrinsic spread in CNO (at a given metallicity), if present at all, is negligible. A more straightforward procedure would be a direct calculation of the measurement error on the [C+N+O/Fe] quantity, which depends on the error on the temperature, gravity, metallicity, microturbulence, and S/N, but this is out of the scope of this paper.…”

Section: The Age Spread and The Age-metallicity Relationmentioning

confidence: 92%

The METALLICITY SPREAD AND THE AGE-METALLICITY RELATION OF Ω CENTAURI

Villanova

Geisler

Gratton

et al. 2014

ApJ

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ω Centauri is a peculiar globular cluster formed by a complex stellar population. To investigate it, we studied 172 stars belonging to the five SGBs that we can identify in our photometry, in order to measure their [Fe/H] content as well as estimate their age dispersion and the age-metallicity relation. The first important result is that all of these SGBs have a distribution in metallicity with a spread that exceeds the observational errors and typically displays several peaks that indicate the presence of several subpopulations. We were able to identify at least six of them based on their mean [Fe/H] content. These metallicity-based subpopulations are seen to varying extents in each of the five SGBs. Taking advantage of the age sensitivity of the SGB, we showed that, first of all, at least half of the subpopulations have an age spread of at least 2 Gyr. Then, we obtained an age-metallicity relation that is the most complete to date for this cluster. Interpretation of the age-metallicity relation is not straightforward, but it is possible that the cluster (or what we can call its progenitor) was initially composed of two populations with different metallicities. Because of their age, it is very unlikely that the most metal-rich derives from the most metal-poor by some kind of chemical evolution process, so they can be assumed to be two independent primordial objects, or perhaps two separate parts of a single larger object, that merged in the past to form the present-day cluster.

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“…Among all the other Galactic GCs with secure evidence of multiple stellar populations, M4 is the least massive one with a metallicity comparable to that of NGC 6362 (Harris 1996(Harris , 2010Marino et al 2008;Carretta et al 2009;Villanova & Geisler 2011). Hence, a comparison between these two clusters could yield particularly interesting information, and, by following the approach described in Mucciarelli et al (2013a), we therefore adopted the same technique described above to perform the chemical analysis of a sample of stars in M4.…”

Section: Comparison With M4mentioning

confidence: 99%

NGC 6362: The Least Massive Globular Cluster With Chemically Distinct Multiple Populations*

Mucciarelli

Dalessandro

Massari

et al. 2016

ApJ

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We present the first measure of Fe and Na abundances in NGC 6362, a low-mass globular cluster (GC) where firstand second-generation stars are fully spatially mixed. A total of 160 member stars (along the red giant branch (RGB) and the red horizontal branch (RHB)) were observed with the multi-object spectrograph FLAMES at the Very Large Telescope. We find that the cluster has an iron abundance of [Fe/H] = −1.09 ± 0.01 dex, without evidence of intrinsic dispersion. On the other hand, the [Na/Fe] distribution turns out to be intrinsically broad and bimodal. The Na-poor and Na-rich stars populate, respectively, the bluest and the reddest RGBs detected in the color-magnitude diagrams including the U filter. The RGB is composed of a mixture of first-and secondgeneration stars in a similar proportion, while almost all the RHB stars belong to the first cluster generation. To date, NGC 6362 is the least massive GC where both the photometric and spectroscopic signatures of multiple populations have been detected.

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Bimodality of light and s-elements in M4 (NGC 6121)

Cited by 68 publications

References 40 publications

Lithium and sodium in the globular cluster M 4

Lithium and sodium in the globular cluster M 4

The METALLICITY SPREAD AND THE AGE-METALLICITY RELATION OF Ω CENTAURI

NGC 6362: The Least Massive Globular Cluster With Chemically Distinct Multiple Populations*

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