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arXiv · 1105.1523

The two metallicity groups of the globular cluster M22: a chemical perspective

A. F. Marino·C. Sneden·R. P. Kraft·G. Wallerstein·J. E. Norris·G. Da Costa·A. P. Milone·I. I. Ivans·G. Gonzalez·J. P. Fulbright·M. Hilker·G. Piotto·M. Zoccali·P. B. Stetson
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Abstract

We present a detailed chemical composition analysis of 35 red giant stars in the globular cluster M22. High resolution spectra for this study were obtained at five observatories, and analyzed in a uniform manner. We have determined abundances of representative light proton-capture, alpha, Fe-peak and neutron-capture element groups. Our aim is to better understand the peculiar chemical enrichment history of this cluster, in which two stellar groups are characterized by a different content in iron, neutron capture elements Y, Zr and Ba, and alpha element Ca. The principal results of this study are: (i) substantial star-to-star metallicity scatter (-2.0<[Fe/H]<-1.6); (ii) enhancement of s-process/r-process neutron-capture abundance ratios in a fraction of giants, positively correlated with metallicity; (iii) sharp separation between the s-process rich and s-process poor groups by [La/Eu] ratio; (iv) possible increase of [Cu/Fe] ratios with increasing [Fe/H], suggesting that this element also has a significant s-process component; and (v) presence of Na-O and C-N anticorrelations in both the stellar groups.

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A. F. Marino, C. Sneden, R. P. Kraft, G. Wallerstein, J. E. Norris, G. Da Costa, A. P. Milone, I. I. Ivans, G. Gonzalez, J. P. Fulbright, M. Hilker, G. Piotto, M. Zoccali, P. B. Stetson. 2011-05-08. The two metallicity groups of the globular cluster M22: a chemical perspective. https://doi.org/10.1051/0004-6361/201116546

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