IR EMISSION FROM CARBON-DUST IN NEBULAE

The relevance of dust in circumstellar emission has to be carefully co nsidered in order to properly interpret astronomical observations. In this work we focus on carbon-rich planetary nebulae in order to produc e models able to account for IR and submillimeter dust emission. The e ffects of dust selective absorption on the ionization structure are in vestigated by means of dust opacities measured in laboratory experimen ts. The infrared spectrum emitted by dust present in both ionized and neutral circumstellar regions is calculated for various choices of the model parameters. The IR dust continuum emission in planetary nebula NGC 7027 is also modelled on the basis of a possible evolutionary scen ario for carbon dust grains. Our results provide evidence that by mean s of UV dust processing it is possible to account for most of the spec tral distribution of carbon-rich planetary nebulae. However, non-equil ibrium emission is needed to explain near-IR bands and part of the und erlying continuum.