Signatures of recent star formation in ring S0 galaxies
  We present a study of the stellar populations of ring and/or arm-like
structures in a sample of S0 galaxies using GALEX far- and near-ultraviolet
imaging and SDSS optical data. Such structures are prominent in the UV and
reveal recent star formation. We quantitatively characterize these rejuvenation
events, estimating the average age and stellar mass of the ring structures, as
well as of the entire galaxy. The mass fraction of the UV-bright rings is a few
percent of the total galaxy mass, although the UV ring luminosity reaches 70%
of the galaxy luminosity. The integrated colors of these S0s locates them in
the red sequence (NGC 2962) and in the so-called green valley. We suggest that
the star formation episodes may be induced by different triggering mechanisms,
such as the inner secular evolution driven by bars, and interaction episodes.
