Stellar populations in the bulges of isolated galaxies
  We present photometry and long-slit spectroscopy for 12 S0 and spiral
galaxies selected from the Catalogue of Isolated Galaxies. The structural
parameters of the sample galaxies are derived from the Sloan Digital Sky Survey
i-band images by performing a two-dimensional photometric decomposition of the
surface brightness distribution. This is assumed to be the sum of the
contribution of a S\`ersic bulge, an exponential disc, and a Ferrers bar
characterized by elliptical and concentric isophotes with constant ellipticity
and position angles. The rotation curves and velocity dispersion profiles of
the stellar component are measured from the spectra obtained along the major
axis of galaxies. The radial profiles of the H{\beta}, Mg and Fe line-strength
indices are derived too. Correlations between the central values of the Mg 2
and Fe line-strength indices and the velocity dispersion are found. The mean
age, total metallicity and total {\alpha}/Fe enhancement of the stellar
population in the centre and at the radius where the bulge gives the same
contribution to the total surface brightness as the remaining components are
obtained using stellar population models with variable element abundance
ratios. We identify intermediate-age bulges with solar metallicity and old
bulges with a large spread in metallicity. Most of the sample bulges display
super-solar {\alpha}/Fe enhancement, no gradient in age and negative gradients
of metallicity and {\alpha}/Fe enhancement. These findings support a formation
scenario via dissipative collapse where environmental effects are remarkably
less important than in the assembly of bulges of galaxies in groups and
clusters.
