Spectral energy distribution of HR 4049. The ISO-SWS spectrum (grey line), and IRAS 25, 60, and 100 μm, and SCUBA 850 μm photometry (grey boxes). The green line is the fit with a single blackbody (1200 K, in accordance with Dominik et al. 2003). The spectral energy distribution of our model (blue) underestimates the flux at λ > 20 μm. The red line shows our model plus a 200 K blackbody, scaled to the SCUBA 850 μm flux. See Sect. 7 for details.