We have performed a new abundance analysis of Carina red giant ( RG ) stars from spectroscopic data collected with UVES ( high spectral resolution ) and FLAMES/GIRAFFE ( high and medium resolution ) at ESO/VLT .
The former sample includes 44 RGs , while the latter consists of 65 ( high-resolution ) and \sim 800 ( medium-resolution ) RGs , covering a significant fraction of the galaxy ’ s RG branch , and red clump stars .
To improve the abundance analysis at the faint magnitude limit , the FLAMES/GIRAFFE data were divided into ten surface gravity and effective temperature bins .
The spectra of the stars belonging to the same gravity and temperature bin were stacked .
This approach allowed us to increase the signal-to-noise ratio in the faint magnitude limit ( V \geq 20.5 mag ) by at least a factor of five .
We took advantage of the new photometry index c _ { U,B,I } introduced recently as an age and probably a metallicity indicator to split stars along the red giant branch .
These two stellar populations display distinct [ Fe/H ] and [ Mg/H ] distributions : their mean iron abundances are –2.15 \pm 0.06 dex ( \sigma =0.28 ) , and –1.75 \pm 0.03 dex ( \sigma =0.21 ) , respectively .
The two iron distributions differ at the 75 % level .
This supports preliminary results .
Moreover , we found that the old and intermediate-age stellar populations have mean [ Mg/H ] abundances of –1.91 \pm 0.05 dex ( \sigma =0.22 ) and –1.35 \pm 0.03 dex ( \sigma =0.22 ) ; these differ at the 83 % level .
Carina ’ s \alpha -element abundances agree , within 1 \sigma , with similar abundances for field halo stars and for cluster ( Galactic and Magellanic ) stars .
The same outcome applies to nearby dwarf spheroidals and ultra-faint dwarf galaxies in the iron range covered by Carina stars .
Finally , we found evidence of a clear correlation between Na and O abundances , thus suggesting that Carina ’ s chemical enrichment history is quite different from that in the globular clusters .