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Title: | A Chemical Trompe-L'oeil: No Iron Spread in the Globular Cluster M22 | Authors: | Mucciarelli, A. Lapenna, E. Massari, D. PANCINO, ELENA Stetson, P. B. Ferraro, F. R. Lanzoni, B. Lardo, C. |
Issue Date: | 2015 | Journal: | THE ASTROPHYSICAL JOURNAL | Number: | 809 | Issue: | 2 | First Page: | 128 | Abstract: | We present the analysis of high-resolution spectra obtained with UVES and UVES-FLAMES at the Very Large Telescope of 17 giants in the globular cluster (GC) M22, a stellar system suspected to have an intrinsic spread in iron abundance. We find that when surface gravities are derived spectroscopically (in order to obtain the same iron abundance from Fe i and Fe ii lines) the [Fe/H] distribution spans ̃0.5 dex, according to previous analyses. However, the gravities obtained in this way correspond to unrealistically low stellar masses (0.1-0.5 {M}<SUB>☉ </SUB>) for most of the surveyed giants. Instead, when photometric gravities are adopted, the [Fe ii/H] distribution shows no evidence of spread, in variance with the [Fe i/H] distribution. This difference has been recently observed in other clusters and could be due to non-local thermodynamical equilibrium effects driven by over-ionization mechanisms that mainly affect the neutral species (thus providing lower [Fe i/H]), but leave [Fe ii/H] unaltered. We confirm that the s-process elements show significant star-to-star variations and their abundances appear to be correlated with the difference between [Fe i/H] and [Fe ii/H]. This puzzling finding suggests that the peculiar chemical composition of some cluster stars may be related to effects able to spuriously decrease [Fe i/H]. We conclude that M22 is a GC with no evidence of intrinsic iron spread, ruling out that it has retained the supernovae ejecta in its gravitational potential well. <P />Based on observations collected at the ESO-VLT under programs 068.D-0332, 071.D-0217 and 073.D-0211. | Acknowledgments: | We warmly thank the anonymous referee for suggestions in improving the paper. We kindly acknowledge P. Bonifacio, B. Dias, R. Gratton, L. Mashonkina, T. Merle, and L. Monaco for comments, help, and suggestions. This research is part of the project COSMIC-LAB ( http://www.cosmic-lab.eu ) funded by the European Research Council (under contract ERC-2010-AdG-267675). | URI: | http://hdl.handle.net/20.500.12386/23104 | URL: | https://iopscience.iop.org/article/10.1088/0004-637X/809/2/128 | ISSN: | 0004-637X | DOI: | 10.1088/0004-637X/809/2/128 | Bibcode ADS: | 2015ApJ...809..128M | Fulltext: | open |
Appears in Collections: | 1.01 Articoli in rivista |
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