y,y − J (top), b,b − J (middle), v,v − J (bottom) CMDs of NGC 6528. Stars were selected according to proper motions and photometric accuracy and were corrected for differential reddening. The red solid and green dashed lines display cluster isochrones at fixed age but different chemical compositions. The blue dotted and purple dotted-dashed lines display younger isochrones for the same chemical compositions (see labeled values). The cluster isochrones are based on evolutionary models computed by assuming either a scaled solar (s-s, red solid and blue dotted) or an α-enhanced (α-e) chemical mixture (green dashed and purple dotted-dashed). Orange and cyan filled dots mark RGs with spectroscopic abundances from ZO04 and SA12, respectively. The two horizontal arrows mark the location of the RHB (brighter) and of the RGB bump (fainter), while the right bent arrow shows the reddening vector. The adopted true distance modulus, mean reddening and error bars are labeled.