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The NIR Ca II triplet absorption lines have proven to be an important toolfor quantitative spectroscopy of individual red giant branch stars in the LocalGroup, providing a better understanding of metallicities of stars in the MilkyWay and dwarf galaxies and thereby an opportunity to constrain their chemicalevolution processes. An interesting puzzle in this field is the significantlack of extremely metal-poor stars, below [Fe/H]=-3, found in classical dwarfgalaxies around the Milky Way using this technique. The question arises whetherthese stars are really absent, or if the empirical Ca II triplet method used tostudy these systems is biased in the low-metallicity regime. Here we presentresults of synthetic spectral analysis of the Ca II triplet, that is focused ona better understanding of spectroscopic measurements of low-metallicity giantstars. Our results start to deviate strongly from the widely-used and linearempirical calibrations at [Fe/H]<-2. We provide a new calibration for Ca IItriplet studies which is valid for -0.5<[Fe/H]<-4. We subsequently apply thisnew calibration to current data sets and suggest that the classical dwarfgalaxies are not so devoid of extremely low-metallicity stars as was previouslythought.

The NIR Ca II triplet at low metallicity - Searching for extremely low-metallicity stars in classical dwarf galaxies