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Title:
Lithium and sodium in the globular cluster M 4. Detection of a Li-rich dwarf star: preservation or pollution?
Authors:
Monaco, L.; Villanova, S.; Bonifacio, P.; Caffau, E.; Geisler, D.; Marconi, G.; Momany, Y.; Ludwig, H.-G.
Affiliation:
AA(European Southern Observatory, 19001 Casilla, Santiago, Chile ), AB(Universidad de Concepción, 160-C Casilla, Concepción, Chile), AC(GEPI, Observatoire de Paris, CNRS, Univ. Paris Diderot, Place Jules Janssen, 92190, Meudon, France), AD(Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, 69117, Heidelberg, Germany; GEPI, Observatoire de Paris, CNRS, Univ. Paris Diderot, Place Jules Janssen, 92190, Meudon, France; ), AE(Universidad de Concepción, 160-C Casilla, Concepción, Chile), AF(European Southern Observatory, 19001 Casilla, Santiago, Chile), AG(European Southern Observatory, 19001 Casilla, Santiago, Chile), AH(Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, 69117, Heidelberg, Germany; GEPI, Observatoire de Paris, CNRS, Univ. Paris Diderot, Place Jules Janssen, 92190, Meudon, France)
Publication:
Astronomy & Astrophysics, Volume 539, id.A157, 7 pp. (A&A Homepage)
Publication Date:
03/2012
Origin:
EDP Sciences
Astronomy Keywords:
nuclear reactions, nucleosynthesis, abundances, stars: abundances, stars: Population II, galaxies: abundances, globular clusters: individual: M4, cosmology: observations
DOI:
10.1051/0004-6361/201117709
Bibliographic Code:
2012A&A...539A.157M

Abstract

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.

Based on observations taken at ESO VLT Kueyen telescope (Cerro Paranal, Chile, program: 085.D-0537A).Table A.1 is available in electronic form at http://www.aanda.org

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