[C/Fe], [N/Fe], and [C/N] abundance ratios as a function of the stellar luminosity (left panels) and temperature (right panels) for the 27 RSGs in the Perseus complex. Values are solar-scaled according to the Grevesse & Sauval (1998) solar reference. Typical error bars are reported in the left upper or lower corner of each panel. For comparison, the PARSEC model predictions for a 9 M_⊙ (blue lines) and a 14 M_⊙ (red lines) star are also plotted.