Top: observed spectra of DQ Tau (in color) with the best-fitting CO₂, H₂O, and HCN slab models fitted for the 13.4–15.1 µm wavelength range. For clarity, the models for the individual molecules (gray curves) were shifted along the y axis. The total model (in black) is the sum of the three individual models and is not shifted. Bottom: ${\chi }_{\min }^2/{\chi }^2$ surfaces with the 1σ, 2σ, 3σ contours marked in green and the centroid marked with the blue asterisk. The color scale goes from 0 (black) to 1 (white). The blue curves show the best-fitting slab radii for certain N-T pairs assuming a circular emitting area.