log(g)–T_eff diagram of two sub-samples of APOKASC RGB stars with average [Fe/H]=-0.35 and mass 1.1 M_⊙, but different α–enhancements: scaled solar objects ([α/Fe] < 0.07, filled circles) and α–enhanced (average [α∕Fe] = 0.2, open circles). Our 1.1 M_⊙, [Fe/H] = −0.35 evolutionarytracks for [α∕Fe] = 0 (solid line) and + 0.40 (dashed line) are also displayed. The α-enhancement of the theoretical models is twice the average enhancement of the selected α-enhanced stars. Dotted and dot-dashed lines show tracks with the same mass, [Fe/H] and α-enhancements, from Dotter et al. (2008).