1997A&A...327.1123P

New high resolution mid-infrared images of the inner part of the β Pictoris circumstellar dust disk are reported. These data are used to probe the inner disk geometry and to derive the 0-100AU radial density profile, with a spatial resolution of 5AU. Realistic grains (porous silicates with a core of olivine and pyroxene coated with a mantle ``organic refractories'') rather than solid Draine and Lee silicates, have been incorporated in models describing the dust thermal emission. In a first set of models, we assume a single composition for the grains. These models are not able to fully reproduce simultaneously our data and the IRAS fluxes. In a second set of models, we introduce another component, consisting of particles containing some ice beyond a limit around 90-100AU. Such a model fulfils all the observational constraints (including the visible scattered flux) and resolves the discrepancy concerning the particles albedo which is predicted to be too small in the first set of models. It also predicts an ice feature at 50µm; a feature around 6µm characteristic of the organic refractory material; and several crystalline olivine features at 24, 28 and 35µm. These features should be observable with the Short Wavelength Spectrometer (SWS) and Long Wavelength Spectrometer (LWS) on board the Infrared Space Observatory. 20µm images should also show an abrupt cut-off around 90-100AU due to the change of the grains composition. ISOCAM should image essentially the scattered starlight, showing the transition between the thermal emission of the inner, non-icy, component, and the scattered emission in the mid-infrared range from the outer component containing ice.