Top panels: proper motion vector–point diagram with a ~8-yr time baseline between HAWK-I and WFI data. The (0, 0) location in VPD is the mean motion of cluster stars candidates. Bottom panels: V vs. (V − K_S) color–magnitude diagram. Left: the entire sample. Center: stars in VPD with proper motion within 4 mas yr^-1 around the cluster mean. Right: probable background/foreground field stars in the area of NGC 6656 studied in this paper. The ellipse that encloses most of the field stars is centered at (−11.8, 1.2) mas yr^-1 with major and minor axes of 12.5 and 14.8 mas yr^-1, respectively.