Medians of the ¹³CO (3–2) and C¹⁸O (3–2) simulated T Tauri line luminosities for different mass bins, presented with red and blue dots in panels a) and b), respectively (i = 10°). The red and blue lines show the fit function of the line luminosity as a function of disk mass. The dotted black lines present the transition mass between the linear and the logarithmic dependence of the line luminosity on the mass (see Eq. (3)). The colored bands show the maximum and minimum simulated line luminosities for the different mass bins.