Positions of stars of several OCs in the log g versus T_eff diagram together with PARSEC evolutionary sequences by Bressan et al. (2012) corresponding to the OC age and metallicity. The RGB luminosity bump is highlighted by the grey thick stick. The red symbols mark the first ascent giants located below the red giant branch luminosity bump (BB), the blue symbols mark stars above the red giant branch luminosity bump (AB) where extra-mixing processes are acting, and the yellow symbols mark helium core burning stars (RC).