Magnitude–distance diagram for the group FGS20. The distance from the BGG is given as a function of the magnitude for each galaxy. The black points represent all the galaxies within the FoV, gray circles are the target galaxies (see Sect. 3.2 for details), red stars represent the spectroscopically confirmed members, and black crosses are the spectroscopically confirmed non-members. The horizontal solid red line corresponds to 0.5 R₂₀₀, the dash-dotted black line marks R₂₀₀, and the dashed black line represents 0.5 Mpc, which is the limit used by Santos et al. (2007) to define the fossilness of the group. The solid red and dash-dotted vertical lines indicate the 2-mag and 2.5-mag gaps from the BGG, which determine the fossilness of the group following the criteria by Jones et al. (2003) and Dariush et al. (2010), respectively.