Equivalent width of N iiiλ4640 as a function of T_eff, for MW and SMC models at log g = 4.0 and mass-loss rates scaled according to Z (see text). Solid/black and dashed(-dotted)/red curves refer to MW series “E” and SMC series “D” models, respectively (Δlog Q =  −0.35 dex). Upper panel: [N] = 7.78 for both Galactic and SMC models. Middle panel: comparison accounting for the theoretically expected maximum [N] enrichment, drawn from tailored evolutionary calculations by Brott et al. (2011a): MW models with [N] = 8.18 and SMC models with [N] = 7.58. Lower panel: SMC series “D” models, with [N] = 7.58 (dashed-dotted) and [N] = 7.78 (dashed). The line emission increases with increasing [N].