  We present a new stellar population synthesis model, which predicts SEDs for
single-age single-metallicity stellar populations, SSPs, at resolution 1.5A
(FWHM) in the spectral region of the near-IR CaII triplet feature. The main
ingredient of the model is a new extensive empirical stellar spectral library
presented in Cenarro et al., which is composed of more than 600 stars. Two main
products of interest for stellar population analysis are presented. The first
is a library of SEDs for SSPs covering a large range of ages, metallicities and
different IMF types. They are well suited to model galaxy data, since the SSP
spectra, with flux-calibrated response curves, can be smoothed to match the
resolution of galaxy data, taking into account the internal velocity dispersion
of the galaxy, allowing the user to analyze the observed spectrum in its own
system. We also produce integrated absorption line indices for the same SSPs in
the form of equivalent widths. We find the following behaviour for the CaII
feature in old-aged SSPs: i) the CaII triplet feature does not change much with
time for all metallicities for ages larger than ~3 Gyr, ii) this index shows a
strong dependence with metallicity for values below [M/H] ~-0.5 and iii) for
larger metallicities this feature does not show a significant dependence either
on age or on the metallicity, being more sensitive to changes in the slope of
power-like IMF shapes. The SSP spectra have been calibrated with measurements
for globular clusters. Fitting the models to two early-type galaxies of
different luminosities, we find that the CaII measurements cannot be fitted
unless a very dwarf-dominated IMF is imposed, or if the Ca abundance is even
lower than the Fe abundance.
