  Synthetic spectra for single-aged stellar populations of metallicities [M/H]
= -0.5, 0.0 and +0.5, ages = 3 to 17 Gyrs, and initial mass function exponents
x = 0.1 to 2.0 were built in the wavelength range 6000-10200 Angstrons. For
such we have employed the grid of synthetic spectra described in Schiavon &
Barbuy (1999), computed for the stellar parameters 2500 <= Teff <= 6000 K, -0.5
<= log g <= 5.0, [M/H] = -0.5, 0.0 and +0.5, and [alpha/Fe] = 0.0, together
with the isochrones by Bertelli et al. (1994) and Baraffe et al. (1998). The
behavior of the features NaI8190, CaII8662, TiO6600 and FeH9900 in the
integrated spectra of single stellar populations were studied in terms of
metallicity, initial mass function and age variations. The main conclusions are
that the NaI doublet is an IMF-sensitive feature, which is however sensitive
also to metallicity and age, whereas TiO, CaII and FeH are very sensitive to
metallicity and essentially insensitive to IMF and age.
