Continuum subtracted spectra comparing the optically thick (solid black) and optically thin (light grey area) approach using only warm forsterite (model RW30). Models are fitted to the 69 μm feature shape. Overplotted are the Spitzer spectrum between 7 and 35 μm and the PACS spectrum between 65 and 73 μm (dark grey lines). A more detailed version comparing the optically thick model and observations can also be found in Fig. 5, panel RW30.