The formation of the Milky Way halo and its dwarf satellites; a NLTE-1D abundance analysis

We present a homogeneous set of accurate atmospheric parameters for a complete sample of very and extremely metal-poor stars in the dwarf spheroidal galaxies (dSphs) Sculptor, Ursa Minor, Sextans, Fornax, Botes I, Ursa Major II, and Leo IV. We also deliver a Milky Way (MW) comparison sample of giant stars covering the 4 3 : 5 regime, the Tii/Tiii ionisation equilibrium is fulfilled in the NLTE calculations. In the logg T-eff plane, all the stars sit on the giant branch of the evolutionary tracks corresponding to [Fe /H] = 2 to 4, in line with their metallicities. For some of the most metal-poor stars of our sample, we achieve relatively inconsistent NLTE abundances from the two ionisation stages for both iron and titanium. We suggest that this is a consequence of the uncertainty in the T-eff-colour relation at those metallicities. The results of this work provide the basis for a detailed abundance analysis presented in a companion paper.