Upper panels, from left to right: Na-O anti-correlation for NGC 288 (Carretta et al. 2009a,b), M 80 (this work), and M 4 (NGC 6121, Carretta et al. 2009a,b). The vertical dotted line indicates the reach of the lowest [O/Fe] ratio measured in M 80, and it is superimposed to the two other GCs for comparison. Lower panels: M_V vs. V − I CMDs for the three GCs from the ACS survey by Sarajedini et al. (2007). Distance moduli and reddening values are from Harris (1996).