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Abstract: We use abundances of Ca, O, Na, Al from high resolution UVES spectra of 200red giants in 17 globular clusters GCs to investigate the correlation foundby Lee et al. 2009 between chemical enrichment from SN II and star-to-starvariations in light elements in GC stars. We find that i the Ca-Hvariations between first and second generation stars are tiny in most GCs~0.02-0.03 dex, comparable with typical observational errors. In addition,ii using a large sample of red giants in M 4 with abundances from UVESspectra from Marino et al. 2008, we find that Ca and Fe abundances in the twopopulations of Na-poor and Na-rich stars are identical. These facts suggestthat the separation seen in color-magnitude diagrams using the U band or hkindex as observed in NGC 1851 by Han et al. 2009 are not due to Cavariations. Small differences in Ca-H as associated to hk variations might bedue to a small systematic effect in abundance analysis, because mostO-poor-Na-rich He-rich stars have slightly larger Fe-H by 0.027 dex onaverage, due to decreased H in the ratio than first generation stars and arethen located at redder positions in the V,hk plane. While a few GCs M 54,omega Cen, M 22, maybe even NGC 1851 do actually show various degree ofmetallicity spread, our findings eliminate the need of a close link between theenrichment by core-collapse SNe with the mechanism responsible for the Na-Oanticorrelation.



Autor: Eugenio Carretta 1, Angela Bragaglia 1, Raffaele Gratton 2, Sara Lucatello 2,3, Michele Bellazzini 1, Valentina D'Orazi 2 1I

Fuente: https://arxiv.org/







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