Same as Fig. 12 but in this case the comparison is with models from the Buzzoni (1989) set, to illustrate the effects of the HB morphology on Hβ. The lower continuous line is an age = 15 Gyr model that splits in two branches around Mg₂ = 0.12 (i.e., in the low metallicity regime) according to the HB morphology associated to the model, i.e., red (RHB) or intermediate (IHB). The latter was chosen because it provides Hβ values (slightly) higher than the BHB case. The dashed line is an age = 15 Gyr model with enhanced oxygen abundance to show the effect of α-enhancement.