Synthetic Spectra for Single-Aged Populations

Spectra of single-aged old stellar populations of metallicities in the range −1.0 ≤ [Fe/H] ≤ +0.5 are built in the wavelength range 6950-7550 Å including TiO bands, by combining synthetic spectra of individual stars. Two approaches are applied: one for moderately metal-poor populations, entirely based on isochrones, and the other one applied to the metal-rich Galactic globular clusters, based on isochrones for the main sequence and data of observed colour-magnitude diagrams for the evolved stages. Abundance ratios of [α/Fe] = +0.3 are adopted for populations of [Fe/H] = −1.0, −0.5, and both 0.0 and +0.3 for the more metal-rich ones.