| Issue |
A&A
Volume 539, March 2012
|
|
|---|---|---|
| Article Number | A157 | |
| Number of page(s) | 7 | |
| Section | Galactic structure, stellar clusters and populations | |
| DOI | https://doi.org/10.1051/0004-6361/201117709 | |
| Published online | 13 March 2012 | |
Lithium and sodium in the globular cluster M 4
Detection of a Li-rich dwarf star: preservation or pollution?⋆,⋆⋆
1 European Southern Observatory, 19001 Casilla, Santiago, Chile
e-mail: lmonaco@eso.org
2 Universidad de Concepción, 160-C Casilla, Concepción, Chile
3 GEPI, Observatoire de Paris, CNRS, Univ. Paris Diderot, Place Jules Janssen, 92190 Meudon, France
4 Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, 69117 Heidelberg, Germany
Received: 15 July 2011
Accepted: 27 January 2012
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.
Key words: nuclear reactions, nucleosynthesis, abundances / stars: abundances / stars: Population II / galaxies: abundances / globular clusters: individual: M4 / cosmology: observations
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
© ESO, 2012
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.