Recent Star-Forming Activity in Local Elliptical Galaxies
  The formation and evolution of elliptical galaxies (EGs) is still an open
question. In particular, recent observations suggest that elliptical galaxies
are not only simple spheroidal systems of old stars. In this paper we analyze a
sample of elliptical galaxies selected from the Sloan Digital Sky Survey in
order to study the star-forming activity in local elliptical galaxies. Among
these 487 ellipticals we find that 13 EGs show unambiguous evidence of recent
star-formation activity betrayed by conspicuous nebular emission lines. Using
the evolutionary stellar population synthesis models and Lick absorption line
indices we derive stellar ages, metallicities, and $\alpha$-element abundances,
and thus reconstruct the star formation and chemical evolution history of the
star-forming elliptical galaxies (SFEGs) in our sample.
  We find that SFEGs have relative younger stellar population age, higher
metallicity, and lower stellar mass, and that their star formation history can
be well described by a recent minor and short starburst superimposed on old
stellar component. We also detect 11 E+A galaxies whose stellar population
properties are closer to those of quiescent (normal) ellipticals than to
star-forming ones. However, from the analysis of their absorption line indices,
we note that our E+A galaxies show a significant fraction of intermediate-age
stellar populations, remarkably different from the quiescent galaxies. This
might suggest an evolutionary link between E+As and star-forming ellipticals.
Finally, we confirm the relations between age, metallicity, $\alpha$ element
abundance, and stellar mass for local elliptical galaxies.
