Marino, A. F.Sneden, ChrisKraft, R. P.Wallerstein, GNorris, JohnDa Costa, GaryMilone, A. P.Ivans, IneseGonzalez, G.Fulbright, J.P.Hilker, MPiotto, GZoccali, M2015-12-100004-6361http://hdl.handle.net/1885/70188We present a detailed chemical composition analysis of 35 red giant stars in the globular cluster M 22. 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, α, 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 α 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.Author/s retain copyrightKeywords: Abundance ratios; Chemical composition analysis; Globular clusters; Globular clusters: individual; High-resolution spectra; Metallicities; Neutron capture; Red giants; S-process; Stars: abundances; Stars: Population II; Techniques: spectroscopic; Astrophy Globular clusters: individual: M 22 (NGC 6656); Stars: abundances; Stars: Population II; Techniques: spectroscopic201110.1051/0004-6361/2011165462016-02-24