Fits on synthetic observations of an externally heated Bonnor-Ebert sphere. Frames a–c show the mass-weighted average LOS temperature of the model cloud and the calculated 160 μm and 500 μm surface brightness maps. Frames d-e show the temperature maps and frame f shows the 500 μm predictions from the 2-MBB model. Frame g shows the ratio of the estimated and true optical depth (τ/τ₀) as the function of τ₀ for the four cases listed in the legend. The solid lines are moving averages, the shaded regions indicate the 1-σ interval in the τ/τ₀ values, and the individual pixels outside this interval are shown as dots.