The dependence between T_C and β for a model of two layers at temperatures T₀ and T₀ + ΔT, with a ratio 4:1 between the column densities. Each solid curve corresponds to a single value of ΔT, with T₀ = 8, 10, 12, and 14 K along the dashed lines. The open symbols show corresponding results for column density ratios 4:1, 3:1, 2:1, and 1:1 for the T₀ values of 8, 10, 12, and 14 K, respectively. The two dotted lines and the square symbols show the values for Bonnor-Ebert spheres of 0.2, 0.4, 0.8, and 1.60 M_⊙ with no external shielding or spheres shielding by A_V = 2^m. In this figure, the 100 μm intensities were not used.