Modeling the Infrared Emission from the HR 4796A Disk

Abstract

We model the spectral energy distribution (SED) from the mid-infrared to submillimeter 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 micron-wavelength emission.