Modelling the Infrared Emission from the HR 4796 A Disk

We model the spectral energy distribution (SED) from the mid-infrared to submil-limeter of the ring-like disk of HR 4796A, the dustiest A-type star. We consider dust made either of coagulated but otherwise unaltered protostellar interstellar grains, or grains that are highly-processed in a protostellar/protoplanetary nebula with silicate dust annealed and carbon dust oxidized. Both types of dust are successful in reproducing the observed SED, provided that the grains are highly fluffy, with a vacuum volume fraction of ∼ 90%. We find no evidence for the existence of a hot " zodiacal dust " component a few AU from the star, which was suggested by previous workers to account for the 10 µm-wavelength emission. Subject headings: circumstellar matter — dust, extinction — infrared: stars — planetary systems: protoplanetary disks — stars: individual (HR 4796A)