Influence of the C/O ratio on synthetic spectra obtained for the models corresponding to the thermal structures displayed in Fig. 1: T_eff = 3000 K, [s/Fe] = 1 dex, log g = 0, M = 1 M_⊙, [Fe/H] = 0, and C/O ratios as labelled. The U,B,V,V₁,J,H,K bandpasses are plotted in black dashed lines, as well as, in black on the top panel, synthetic spectra of pure TiO and pure ZrO (for the same temperature and C/O = 0.5) to help identifying molecular-band contributors. For the sake of clarity, spectra are also zoomed shortward of 6500 Å.