  We have acquired intermediate resolution spectra in the 3700-7000 A
wavelength range for a sample of 65 early-type galaxies predominantly located
in low density environments, a large fraction of which show emission lines. The
spectral coverage and the high quality of the spectra allowed us to derive Lick
line-strength indices and to study their behavior at different galacto-centric
distances. Ages, metallicities and element abundance ratios have been derived
for the galaxy sample by comparison of the line-strength index data set with
our new developed Simple Stellar Population (SSP) models. We have analyzed the
behavior of the derived stellar population parameters with the central galaxy
velocity dispersion and the local galaxy density in order to understand the
role played by mass and environment on the evolution of early-type galaxies. We
find that the chemical path is mainly driven by the halo mass, more massive
galaxies exhibiting the more efficient chemical enrichment and shorter star
formation timescales. Galaxies in denser environments are on average older than
galaxies in less dense environments. The last ones show a large age spread
which is likely to be due to rejuvenation episodes.
