Spectroscopic and photometric evidence of two stellar populations in the Galactic globular cluster NGC 6121 (M 4)A. F. Marino, S. Villanova, G. Piotto, A. P. Milone, Y. Momany, L. R. Bedin and A. M. MedlingA&A, 490 2 (2008) 625-640DOI: https://doi.org/10.1051/0004-6361:200810389
