Comparison of the H₂ line fluxes (left), CO rovibrational line flux (middle), and the H₂O 33 μm feature flux (right) between models and data. Left panel: the amount of gas within 2.4 AU is varied. Middle and right panels: δ_gas = 0.1 is used and C/H and O/H are varied respectively. Horizontal bands show the 1σ variation of the observed fluxes. The different coloured points denote different values for T_step. The temperature threshold above which the abundances are varied. The vertical lines in the middle and right panel show the volatile carbon and oxygen abundances assumed for the ISM (Meyer et al. 1998; Lacy et al. 2017).