The Sagittarius Dwarf Galaxy Survey (SDGS): constraints on the Star   Formation History of the Sgr dSph
  The main characteristics of a wide photometric survey of the Sgr dwarf spheroidal galaxy are shortly presented. V and I photometry has been obtained for ~ 90000 stars toward Sgr and for ~ 9000 stars in a region devoid of Sgr stars (for decontamination purposes). The full potential of this large database is far from being completely explored. Here we present only preliminary results from the analysis of statistically decontaminated Color Magnitude Diagrams, trying to set a scheme of the Star Formation History of the Sgr Galaxy. A scenario is proposed in which star formation in Sgr began very early and lasted for several Gyr with progressive chemical enrichment of the Inter Stellar Medium (ISM). Nearly 8 Gyr ago the star formation rate abruptly decreased, perhaps in coincidence with the event that led to the gas depletion of the galaxy. A very small rate of star formation continued until relatively recent times (~ 1 Gyr ago). 
M. Bellazzini, F.R. Ferraro and R. Buonanno