We present an analysis of photometric and spectroscopic data of the Carina dSph galaxy , testing a new approach similar to that used to disentangle multiple populations in Galactic globular clusters ( GCs ) .
We show that a proper colour combination is able to separate a significant fraction of the red giant branch ( RGB ) of the two main Carina populations ( the old one , \sim 12 Gyr , and the intermediate–age one , 4 - 8 Gyr ) .
In particular , the { \it c } _ { U,B,I } = ( U - B ) - ( B - I ) pseudo-colour allows us to follow the RGB of both populations along a relevant portion of the RGB .
We find that the oldest stars have more negative { \it c } _ { U,B,I } pseudo-colour than intermediate–age ones .
We correlate the pseudo-colour of RGB stars with their chemical properties , finding a significant trend between the iron content and the { \it c } _ { U,B,I } .
Stars belonging to the old population are systematically more metal poor ( [ Fe/H ] = -2.32 \pm 0.08 dex ) than the intermediate–age ones ( [ Fe/H ] = -1.82 \pm 0.03 dex ) .
This gives solid evidence on the chemical evolution history of this galaxy , and we have a new diagnostic that can allow us to break the age-metallicity degeneracy of H-burning advanced evolutionary phases .
We compared the distribution of stars in the { \it c } _ { U,B,I } plane with theoretical isochrones , finding that no satisfactory agreement can be reached with models developed in a theoretical framework based on standard heavy element distributions .
Finally , we discuss possible systematic differences when compared with multiple populations in GCs .