Relation between [C/Fe] and the luminosity of the very metal-poor RGB stars selected as T_eff< 5300 Å and [Fe/H] < −2.5. The dotted line corresponds to the limits of Aoki et al. (2007) distinguishing between carbon-rich and normal population. The green colour identifies the EMPS in Sextans with a stellar symbol for the analysis of Honda et al. (2011), and with upright triangles for the Tafelmeyer et al. (2010) sample. The blue triangle identifies Fornax (Tafelmeyer et al. 2010). The cyan circles show the observations in Draco by Shetrone et al. (2013) and Kirby et al. (2015), while the point above the dotted line is the carbon-rich RGB found by Cohen & Huang (2009) in this galaxy. The observations of Kirby et al. (2015) in Ursa Minor are shown in purple. The references of the other comparisons samples are given in Sect. 5.1. The Milky Way halo stars are shown in grey. The Sculptor stars are seen in orange. The errors on their luminosities are calculated for a 100 K uncertainty in T_eff . The ultra−faint dwarf spheroidal galaxies are indicated with black symbols. Ursa Major II is identified with upright triangles, Coma Berenices with stars, Leo IV with squares, Hercules with pointing down triangles, Segue I with pointing right triangles, and Boötes with diamonds.