Observed properties of Bonnor-Ebert spheres. The solid squares denote the FWHM of the column density distribution and the true mass of the cores at T_gas = 10 K (blue symbols) or at 20 K (red symbols left of the 10 K points). The circles show the FWHM of the 350 μm surface brightness and the mass estimated from simulated observations at 100 μm and 350 μm. The cores are heated either by the full ISRF (open circles, shown for T_gas = 10 K only) or by the ISRF attenuated by A_V = 4^m (filled circles). Masses are calculated with the correct spectral index, β ~ 2.1, and with one lower and one higher value.