Chemical histories in the Local Group DSphs
G. Marconi¹, L. Sbordone², P. Bonifacio³, L. Monaco¹,
¹ ESO ² INAF, OAR ³ INAF, OAT
Chemical compositions of red giant stars for the Sagittarius (and associated GCs), Canis Major and Fornax DSphs have been derived from HR spectoscopy in order to study the history of chemical enrichment and star formation inside these "building blocks". The results of a wide Ca Triplet survey across the main body of the Sgr galaxy in order to study metallicity gradients and identify the metal poor stellar component will also be presented. The spectroscopic metallicities allow us to break the age-metallicity degeneracy in the interpretation of the colour-magnitude diagram (CMD). Comparison of isochrones of appropriate metallicity with the observed CMD suggests an age of 1 Gyr or younger for the dominant Sgr population sampled by us. We argue that the observations support a star formation that is triggered by the passage of Sgr through the Galactic disc, both in Sgr and in the disc. This scenario has also the virtue of explaining the mysterious "bulge C stars" as disc stars formed in this event.

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