Spectral energy distributions for selected positions. The measurements correspond to a single pixel at the centre of the circles shown in Fig. 4 (after convolution to the resolution of the 500 μm observations). The temperature and the spectral index are quoted in the frames, the first values corresponding to the upper SED curve. The dashed lines are the fits with a constant spectral index value of β = 1.7 or β = 2.3.