Model II: SEDs for the two cores (with radius = 20 pixels) that were marked with numbers 1 and 2 in Fig. 8. The “true” SEDs (see text) are drawn with continuous lines. The observed SEDs (dashed lines) are fits to five wavelengths 100, 160, 250, 350, and 500 μm and the corresponding mean intensities are marked with circles. Core 1 (with small observational mass bias) is marked with black and core 2 (with large observational mass bias) with red colour. For true SEDs: T = true mean temperature of dust grains, β = true spectral index = 2.1, N = true mean column density for the core area. For observed SEDs: T = temperature (given by fit), β = spectral index (given by fit), N = observed mean column density for the core area.