2000ApJ...532..453S

Synthetic spectra for single-aged stellar populations of metallicities [M/H]=-0.5, 0.0, and +0.5, ages=3-17 Gyr, and initial mass function indices x=0.1-2.0 were built in the wavelength range λλ6000-10200. We have employed the grid of synthetic spectra described in Schiavon & Barbuy, computed for the stellar parameters 2500≤T_eff≤6000 K, -0.5≤logg≤5.0, [M/H]=-0.5, 0.0, and +0.5, and [α/Fe]=0.0, together with the isochrones by Bertelli et al. and Baraffe et al. The behavior of the features Na I λ8190, Ca II λ8662, TiO λ6600, and FeH λ9900 Å in the integrated spectra of single-aged stellar populations was studied in terms of metallicity, initial mass function (IMF), and age variations. The main conclusions are that the Na I doublet is an IMF-sensitive feature, which is, however, sensitive also to metallicity and age, whereas TiO, Ca II, and FeH are very sensitive to metallicity and essentially insensitive to IMF and age.