Line-strength comparison. Blue and orange lines indicate, respectively, the FASTAR and MILES predictions for different line-strength indices at a 2.51 Å resolution. Left panel: Equivalent width of the H_βO line is shown as a function of age for a population of solar metallicity and a Milky Way-like IMF. For old ages, FASTAR predictions tend to be lower than those of MILES. Middle panel: dependence of the Mgb feature on metallicity for a 10 Gyr population with a Milky Way-like IMF. Right panel: Behavior of the TiO₂ molecular band for different IMF slope values (single power law) is shown for 10 Gyr and solar metallicity population.