Modeling the infrared emission from the HR 4796A disk. Astrophys

We model the spectral energy distribution (SED) from the mid-infrared to submillimeter of the ringlike disk of HR 4796A, the dustiest A-type star. We consider dust made of either coagulated but otherwise unal-tered protostellar interstellar grains or grains that are highly processed in a protostellar/protoplanetary neb-ula 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 astronomical units from the star, which was suggested by previous workers to account for the 10 lmwavelength emission. Subject headings: circumstellar matter — dust, extinction — infrared: stars — planetary systems: protoplanetary disks — stars: individual (HR 4796A) 1