  We present radial stellar population parameters for a subsample of 12
galaxies from the 36 isolated early-type galaxies of Reda et al. Using new
long-slit spectra, central values and radial gradients for the stellar age,
metallicity [Z/H] and alpha-element abundance [E/Fe] are measured. Similarly,
the central stellar population parameters are derived for a further 5 isolated
early-type galaxies using their Lick indices from the literature. On average,
the seventeen isolated galaxies have mean central [Z/H]o and [E/Fe]o of
0.29+/-0.03 and 0.17+/-0.03 respectively and span a wide range of ages from 1.7
to 15 Gyrs. We find that isolated galaxies follow similar scaling relations
between central stellar population parameters and galaxy velocity dispersion to
their counterparts in high density environments. However, we note a tendency
for isolated galaxies to have slightly younger ages, higher [Z/H] and lower
[E/Fe]. Such properties are qualitatively consistent with the expectation of an
extended star formation history for galaxies in lower density environments.
Generally we measure constant age and [E/Fe] radial gradients. We find that the
age gradients anti-correlate with the central galaxy age. Metallicity gradients
range from near zero to strongly negative. For our high mass galaxies
metallicity gradients are shallower with increasing mass. Such behaviour is not
predicted in dissipational collapse models but might be expected in multiple
mergers. The metallicity gradients correlate with the central age and
metallicity, as well as to the age gradients. In conclusion, our stellar
population data for isolated galaxies are more compatible with an extended
merger/accretion history than early dissipative collapse.
