¹³CO line intensity radial profiles (solid lines) obtained with input surface density distribution Σ_gas (dashed lines) given by the self-similar disk model (see Eq. (1)). The model parameters are M_disk = 10⁻⁴ M_⊙ and γ = 0.8, 1, 1.5 shown in dark blue, light blue, and purple, respectively (top, middle, and bottom panels). Model with R_c = 30, 60, 200 au are presented in panels a, b, and c, respectively.