Parameters of the AS 205 (N) model compared to the formation of the R(6) 10⁰0–00⁰0 line at 3 μm and Q(6) 01¹0–0⁰00 line at 14 μm. The model with a gas-to-dust ratio of 1000 and a constant abundance x_in = x_out = 3 × 10^-8 is shown. a) Density structure. b) Dust temperature. c) Adopted fractional abundance of HCN. d) Continuum radiation field relative to a 750 K blackbody for the R(6) 3 μm line. Overlayed are the τ = 1 surface of the line (red) and continuum (blue) and the region where the critical density of the line is reached (black). e) Excitation temperature of the R(6) 3 μm line. f) Regions with 50 or 75% contribution to the observed flux. g)–i) As panels d)–f), but for the Q(6) 14 μm line.