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Lithium on the lower red giant branch of five Galactic globular clusters

Aguilera-Gómez, C, Monaco, L, Mucciarelli, A, Salaris, M, Villanova, S and Pancino, E (2021) Lithium on the lower red giant branch of five Galactic globular clusters. Astronomy and Astrophysics, 657. ISSN 0004-6361

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Abstract

Context. Lithium is one of the few elements produced during Big Bang nucleosynthesis in the early universe. Moreover, its fragility makes it useful as a proxy for stellar environmental conditions. As such, the lithium abundance in old systems is at the core of various astrophysical investigations. Aims. Stars on the lower red giant branch are key to studies of globular clusters where main sequence stars are too faint to be observed. We use these stars to analyze the initial Li content of the clusters and compare it to cosmological predictions, to measure spreads in Li between different stellar populations, and to study signs of extra depletion in these giants. Methods. We used the GIRAFFE spectra to measure the lithium and sodium abundances of lower red giant branch stars in five globular clusters. These cover an extensive range in metallicity, from [Fe/H] ∼-0.7 to [Fe/H] ∼-2.3 dex. Results. We find that the lithium abundance in these lower red giant branch stars forms a plateau, with values from A(Li)NLTE = 0.84 to 1.03 dex, showing no clear correlation with metallicity. When using stellar evolutionary models to calculate the primordial abundance of these clusters, we recover values of A(Li)NLTE = 2.1 - 2.3 dex, consistent with the constant value observed in warm metal-poor halo stars, namely the Spite plateau. Additionally, we find no difference in the lithium abundance of first and second population stars in each cluster. We also report the discovery of a Li-rich giant in the cluster NGC 3201, with A(Li)NLTE = 1.63 ± 0.18 dex, where the enrichment mechanism is probably pollution from external sources.

Item Type: Article
Additional Information: Lithium on the lower red giant branch of five Galactic globular clusters C. Aguilera-Gómez, L. Monaco, A. Mucciarelli, M. Salaris, S. Villanova and E. Pancino A&A, 657 (2022) A33 Published online: 24 December 2021 DOI: 10.1051/0004-6361/202141750
Uncontrolled Keywords: 0201 Astronomical and Space Sciences
Divisions: Astrophysics Research Institute
Publisher: EDP Sciences
Date Deposited: 25 Jan 2022 10:00
Last Modified: 25 Jan 2022 10:00
DOI or Identification number: 10.1051/0004-6361/202141750
URI: https://researchonline.ljmu.ac.uk/id/eprint/16132

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