Distance to the group center vs. SExtractor r-band magnitude for all galaxies (grey circles). We have also overplotted cluster members (red triangles) and non-cluster members (black circles). The horizontal line shows 500 kpc distance from the galaxy group center (the distance used in the “fossil group” definition). The vertical dotted and dashed lines show Δm₁₂ = 2.0 and Δm₁₄ = 2.5 respectively, taking m_r,SEx as the BGG magnitude.