  With the aim of building a data-set of spectral properties of well studied
early-type galaxies showing emission lines, we present intermediate resolution
spectra of 50 galaxies in the nearby Universe. The sample, which covers several
of the E and S0 morphological sub-classes, is biased toward objects that might
be expected to have ongoing and recent star formation, at least in small
amounts, because of the presence of the emission lines. The emission are
expected to come from the combination of active galactic nuclei and star
formation regions within the galaxies. Sample galaxies are located in
environments corresponding to a broad range of local galaxy densities, although
predominantly in low density environments. Our long-slit spectra cover the 3700
- 7250 A wavelength range with a spectral resolution of about 7.6 A at 5550 A.
The specific aim of this paper, and our first step on the investigation, is to
map the underlying galaxy stellar population by measuring, along the slit,
positioned along the galaxy major axis, line--strength indices at several,
homogeneous galacto-centric distances. For each object we extracted 7
luminosity weighted apertures corrected for the galaxy ellipticity and 4
gradients and we measured 25 line-strength indices. The paper introduces the
sample, presents the observations, describes the data reduction procedures, the
extraction of apertures and gradients, the determination and correction of the
line--strength indices, the procedure adopted to transform them into the
Lick-IDS System and the procedures adopted for the emission correction. We
finally discuss the comparisons between our dataset and line-strength indices
available in the literature.
