Line intensity ratios of HCN(13 → 12)/CO(6 → 5) and H₂O((1_1,0 → 1_0,1))/CO(6 → 5) plotted against each other (top), and of NH₃(1₀ → 0₀)/CO(6 → 5) and H₂O((1_1,0 → 1_0,1))/CO(6 → 5) plotted against each other (bottom). The data are given in Table 8. The red circles are C stars, the blue triangles are M stars, and the two S stars are shown in green with W Aql being the star and χ Cyg the square. In the lower plot, the ratio shown for NH₃/CO for χ Cyg is an upper limit. The χ Cyg values are taken from Schöier et al. (2011).