The Two Metallicity Groups Of The Globular Cluster M22: A Chemical Perspective

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Marino, A. F.
Sneden, Christopher
Kraft, R. P.
Wallerstein, G.
Norris, J. E.
Da Costa, G.
Milone, A. P.
Ivans,, II
Gonzalez, G.
Fulbright, J. P.

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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 less than or similar to [Fe/H] less than or similar to -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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Marino, A. F., Christopher Sneden, R. P. Kraft, G. Wallerstein, J. E. Norris, G. Da Costa, A. P. Milone et al. >The two metallicity groups of the globular cluster M 22: a chemical perspective.> Astronomy & Astrophysics, Vol. 532 (Aug., 2011): A8.