Astronomy and Astrophysics, volume 532A, 8-8 (2011/8-1)
The two metallicity groups of the globular cluster M 22: a chemical perspective.
MARINO A.F., SNEDEN C., KRAFT R.P., WALLERSTEIN G., NORRIS J.E., DA COSTA G., MILONE A.P., IVANS I.I., GONZALEZ G., FULBRIGHT J.P., HILKER M., PIOTTO G., ZOCCALI M. and STETSON P.B.
Abstract (from CDS):
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, 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.
techniques: spectroscopic - stars: abundances - stars: Population II - globular clusters: individual: M22 (NGC 6656)
Table 2 star C is 2MASS J18361022-2348444.
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