Cluster members selection. Procedure carried out to select the probable NGC 2099 cluster members located within ∼30 arcmin from the cluster center. Panel a: stellar proper motions relative to the average cluster motion against the G magnitude. The blue line separates stars with cluster-like proper motions from the remaining stars. Panel b: stellar G magnitude as a function of parallax. Stars with cluster-like parallaxes are located between the two blue lines. The vector point diagram of proper motions is plotted in panel c, whereas panel d shows the spatial stellar distribution. Finally, panel e illustrates the G vs. G_BP − G_RP observed CMD, together with the best-fit isochrone. Likely cluster members are represented with azure crosses, while brown crosses indicate stars with cluster-like proper motions and parallaxes in the reference field.