C/O elemental ratios as a function of [Fe/H] for both oxygen indicators using abundances derived with ATLAS models (filled circles) or MARCS models (open circles). The T_eff of each star is depicted with a colour scale. The magenta and green continuous lines marks the solar C/O value for ATLAS and MARCS models, respectively. The black dashed line marks the limit of C/O values above which planets are considered as carbon-rich.