Procedure to identify the probable stars of NGC 1783 on the blue, bright side of the MS. Top: reproductions of the CMDs of NGC 1783 of Fig. 16. Right panels are zoomed-in views of the CMD region on the bright-blue side of the MSTO (dashed rectangle in the top-left panel) for stars with radial distances from the cluster center smaller and larger than 45 arcsec. Bottom: proper-motion diagram of stars plotted in the top-left panel (left). The red circle separates stars with a cluster-like motion from the bulk of field stars. Black points and aqua-starred symbols mark the selected bright-blue stars. The corresponding histogram distributions for μ_α cos δ and μ_δ are also represented on the top and right side of the panel. The best fit bi-Gaussian functions are represented with gray lines, and the two Gaussian components are colored aqua and red. The bottom-right panel shows the simulated proper motions for cluster members and field stars. Black and blue dots indicate NGC 1783 stars with cluster-like and field-like proper motions, respectively, while red color is used to distinguish field stars with cluster-like proper motions from the remaining field stars (aqua starred symbols).