A double stellar generation in the globular cluster NGC 6656 (M 22) - Two stellar groups with different iron and s-process element abundancesA. F. Marino, A. P. Milone, G. Piotto, S. Villanova, L. R. Bedin, A. Bellini and A. RenziniA&A, 505 3 (2009) 1099-1113DOI: https://doi.org/10.1051/0004-6361/200911827
