In this paper we develop an evolutionary stellar population synthesis model to predict spectral energy distributions , SED ’ s , for single-age , single-metallicity stellar populations , SSP ’ s , at resolution \sim 1.8Å in two narrow , but very important spectral regions around 4000Å and 5000Å .
The input stellar database is composed of a subsample of \sim 550 stars , selected from the original KPNO coude feed stellar spectral library of Jones .
Therefore , this is the first time that an evolutionary model employs such an extensive empirical stellar spectral library , at such high resolution , for supporting its SED ’ s predictions .

A spectral library corresponding to simple old stellar populations with metallicities in the range -0.7 \leq [ Fe / H ] \leq + 0.2 is presented here , as well as an extensive discussion about the most popular system of absorption indices at intermediate resolution , the Lick system , showing the advantages of using the new model predictions .
Also , for the first time is shown the behavior of the system of indices of Rose , at higher resolution , as a function of the age and metallicity of the stellar population .

The newly synthesized model spectra can be used to analyze the observed galaxy spectrum in a very easy and flexible way , allowing us to adapt the theoretical predictions to the characteristics of the data instead of proceeding in the opposite direction as , for example , we should do when transforming the observational data for using model predictions based on a particular instrument-dependent system of indices at a specific resolution .
The synthetic SSP spectra , with flux-calibrated response curve , can be smoothed to the same resolution of the observations , or to the measured galaxy internal velocity dispersion , allowing us to analyze the observed spectrum in its own system .
Therefore we are able to utilize all the information contained in the data , at their spectral resolution .
After performing this step , the entire observational spectrum can be compared at once , or the analysis can be done measuring a particular set of features in the two , the synthesized and the observational spectrum , rather than trying to correct the latter from broadening or instrumental effects .

The SSP model spectra were calibrated at relatively high resolution with two well studied metal-rich globular clusters in our galaxy , 47 Tuc and NGC 6624 , providing very good fits and being able to detect well known spectral peculiarities such as the CN anomaly of 47 Tuc .
The model was also confronted to an early-type galaxy , NGC 3379 , revealing its well known magnesium over iron overabundance , and showing how appropriate are the new model predictions , as well as the way in which they can be used , for studying the elemental ratios of these stellar systems .
In fact , different models of different metallicities provide equal approaches to the galaxy spectrum : once H _ { \beta } is properly constrained , either we are able to fit the iron features ( with a metallicity somewhat in the range -0.4 \leq [ Fe/H ] \leq 0 ) or the magnesium features ( with a metallicity in the range 0 \leq [ Fe/H ] \leq +0.2 ) , but never the two set of indices simultaneously .