Left: full proper motion VPD from the HSTPROMO catalogue. Right: proper motion VPD for stars within the F606W magnitude bin that includes one of the candidate counterparts of X5 (the object shown in blue in Fig. 6). The purple point indicates the object’s position in the VPD along with its associated errors. The blue, orange and red circles represent the 1σ, 2σ, and 3σ contours, respectively.