Stellar Populations in Circumnuclear Star Forming Regions
  We present a study of the stellar populations and gas physical conditions in Circumnuclear Star Forming Regions (CNSFR) based on broad and narrow band photometry and spectrophotometric data, which have been analyzed with the use of evolutionary population synthesis and photoionization models. It is found that most CNSFR show composite stellar populations of slightly different ages. They seem to have the highest abundances in HII region-like objects, showing also N/O overabundances and S/O underabundances by a factor of about three. Also, CNSFR as a class, segregate from the disk HII region family, clustering around smaller $\eta$' values, and thereforefore higher ionizing temperatures. 
A. I. Diaz (UAM), M. Alvarez-Alvarez (UAM), M. Castellanos (UAM)