a) Oxygen in Sculptor as a function of [Fe/H]. Same symbols are used as in Fig. 5. Sculptor stars (blue filled circles) come from Hill et al. (in prep.), Representative error bar for the measurements is shown; b) Carbon in Sculptor as a function of [Fe/H]. Solid points are direct carbon measurements of the stars shown in Fig. 5. Open circles show estimates of C abundances for 85 stars (VLT/FLAMES spectra) from CN molecular lines in the wavelength range 9100–9250 Å. Ratio typical for mixed stars, [ C/N ] = −1.2 (Spite et al. 2005), is assumed, and for stars with unknown oxygen abundance, a simple trend of [O/Fe] with [Fe/H] is adopted, as shown with a line in a). Two stars from Starkenburg et al. (2013) that have the same [C/Fe] at [ Fe/H ] ~ −3 are moved by 0.02 dex to each side, to be visible as two stars. Same is done for two stars with similar C estimates at [ Fe/H ] = −2.35.