Lithium and sodium in the globular cluster M 4 . Detection of a Li-rich dwarf star: preservation or pollution?
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.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- March 2012
- DOI:
- 10.1051/0004-6361/201117709
- arXiv:
- arXiv:1108.0138
- Bibcode:
- 2012A&A...539A.157M
- Keywords:
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- nuclear reactions;
- nucleosynthesis;
- abundances;
- stars: abundances;
- stars: Population II;
- galaxies: abundances;
- globular clusters: individual: M4;
- cosmology: observations;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
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