A chemical trompe-l’oeil: no iron spread in the globular cluster N22

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DOIResolve DOI: http://doi.org/10.1088/0004-637X/809/2/128
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TypeArticle
Journal titleThe Astrophysical Journal
ISSN1538-4357
Volume809
Issue2
Pages128
Subjectstars: abundances; techniques: spectroscopic
AbstractWe 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) 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.
Publication date
LanguageEnglish
AffiliationNational Science Infrastructure; National Research Council Canada
Peer reviewedYes
NPARC number23000653
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Record identifier952af64c-06f9-4dbc-8a61-8aa8f96d8380
Record created2016-08-18
Record modified2016-08-18
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