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The Gaia-ESO Survey: Detailed abundances in the metal-poor globular cluster NGC 4372

I. San Roman, C. MuŮoz, D. Geisler, S. Villanova, N. Kacharov, A. Koch, G. Carraro, G. Tautvai®ienė, A. Vallenari, E. J. Alfaro, T. Bensby, E. Flaccomio, P. Francois, A. J. Korn, E. Pancino, A. Recio-Blanco, R. Smiljanic, M. Bergemann, M. T. Costado, F. Damiani, U. Heiter, A. Hourihane, P. Jofrť, C. Lardo, P. de Laverny, T. Masseron, L. Morbidelli, L. Sbordone, S. G. Sousa, C. Worley, S. Zaggia

Abstract
We present the abundance analysis for a sample of 7 red giant branch stars in the metal-poor globular cluster NGC 4372 based on UVES spectra acquired as part of the Gaia-ESO Survey. This is the first extensive study of this cluster from high-resolution spectroscopy. We derive abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, Fe, Cr, Ni, Y, Ba, and La. We find a metallicity of [Fe/H] = −2.19 ± 0.03 and find no evidence of any metallicity spread. This metallicity makes NGC 4372 one of the most metal-poor Galactic globular clusters. We also find an α-enhancement typical of halo globular clusters at this metallicity. Significant spreads are observed in the abundances of light elements. In particular, we find a Na-O anticorrelation. Abundances of O are relatively high compared with other globular clusters. This could indicate that NGC 4372 was formed in an environment with high O for its metallicity. A Mg-Al spread is also present that spans a range of more than 0.5 dex in Al abundances. Na is correlated with Al and Mgabundances at a lower significance level. This pattern suggests that the Mg-Al burning cycle is active. This behavior can also be seen in giant stars of other massive, metal-poor clusters. A relation between light and heavy s-process elements has been identified.

Keywords
globular clusters: individual: NGC 4372 – stars: abundances

Astronomy and Astrophysics
Volume 579, Number of pages A6
2015 July

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Instituto de Astrof√≠sica e Ci√™ncias do Espa√ßo Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia