We present a new evolutionary stellar population synthesis model , which predicts SEDs for single-age single-metallicity stellar populations , SSPs , at resolution 1.5Å ( FWHM ) in the spectral region of the near-IR Ca ii triplet feature .
The main ingredient of the model is a new extensive empirical stellar spectral library that has been recently presented in Cenarro et al .
( 2001a , b ; 2002 ) , which is composed of more than 600 stars with an unprecedented coverage of the stellar atmospheric parameters .

Two main products of interest for stellar population analysis are presented .
The first is a spectral library for SSPs with metallicities - 1.7 < [ Fe/H ] < +0.2 , a large range of ages ( 0.1-18 Gyr ) and IMF types .
They are well suited to model galaxy data , since the SSP spectra , with flux-calibrated response curves , can be smoothed to the resolution of the observational 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 ( namely CaT ^ { * } , CaT and PaT ) for the same SSPs in the form of equivalent widths .

We find the following behaviour for the Ca ii triplet feature in old-aged SSPs : i ) the strength of the CaT ^ { * } index does not change much with time for all metallicities for ages larger than \sim 3 Gyr , ii ) this index shows a strong dependence with metallicity for values below [ M/H ] \sim - 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 of Armandroff & Zinn ( 1988 ) , which are well reproduced , probing the validity of using the integrated Ca ii triplet feature for determining the metallicities of these systems .
Fitting the models to two early-type galaxies of different luminosities ( NGC 4478 and NGC 4365 ) , we find that the Ca ii triplet measurements can not be fitted unless a very dwarf-dominated IMF is imposed , or if the Ca abundance is even lower than the Fe abundance .
More details can be found in Cenarro et al .
( 2003 ) .