Binary-fraction analysis of Berkeley 32. (a) CMD of the MS stars. The solid line shows the MS; the dashed and dotted lines mark the lower and upper limits of the binary selection region, respectively. Triangle symbols indicate binary candidates. (b) Distribution of ΔG residuals. The shaded region denotes the binary selection zone between the lower and upper limits. (c) Cumulative distribution of ΔG. The binary fraction f_b is indicated by the vertical arrow spanning the two selection limits.