Ratios of CO isotopologue line intensity (J = 3−2) obtained with the NOISO and ISO networks as a function of the disk radius. /I [ ¹³CO ] _ISO, /I [ C¹⁸O ] _ISO and /I [ C¹⁷O ] _ISO were defined. Dotted lines refer to models where f = 10^-2, solid lines to f_large = 0.99. Different colors indicate models with different disk masses: M_d = 10^-4M_⊙ in blue, M_d = 10^-3M_⊙ in light blue and M_d = 10^-2M_⊙ in purple. Models with T Tauri stars are shown in the left panels, those with Herbig stars in the right panels.