Radial profile of the initial disk model for both metallicities Z = 1 Z_⊙ (solid lines) and Z = 0.2 Z_⊙ (dashed lines). The yellow, red, and blue lines indicate models with Ṁ_start = [1 × 10⁻⁹, 5 × 10⁻⁹, and 1 × 10⁻⁸] M_⊙ yr⁻¹, respectively. Panel a shows the disk surface density, Σ, panel b the disk midplane temperature, T_disk, and panel c the optical depth, τ. The thin vertical lines in panel a indicate the respective position of R_c. The horizontal line in panel b indicates the ambient temperature T_amb = 20 K. The horizontal dashed line in panel c symbolizes τ = 1, which divides optically thin regions (τ ≪ 1) from optically thick regions (τ ≫ 1).