  We have measured central line strengths for a magnitude-limited sample of
early-type galaxies in the Fornax cluster, comprising 11 elliptical (E) and 11
lenticular (S0) galaxies, more luminous than MB=-17. When compared with
single-burst stellar population models we find that the centres of Fornax
ellipticals follow a locus of fixed age and have metallicities varying roughly
from half solar to two times solar. The centres of (lower luminosity)
lenticular galaxies, however, exhibit a substantial spread to younger
luminosity-weighted ages indicating a more extended star formation history.
Galaxies with old stellar populations show tight scaling relations between
metal-line indices and the central velocity dispersion. Remarkably also the
Fe-lines are well correlated with sigma. Our detailed analysis of the stellar
populations suggests that these scaling relations are driven mostly by
metallicity. Galaxies with a young stellar component do generally deviate from
the main relation. In particular the lower luminosity S0s show a large spread.
Furthermore we find that elliptical galaxies and the bulge of one bright S0 are
overabundant in magnesium, where the most luminous galaxies show the strongest
overabundances. The stellar populations of young and faint S0s are consistent
with solar abundance ratios or a weak Mg underabundance. (abriged)
