Modeling the Infrared Emission from the HD 141569A Disk

We model the infrared (IR) emission from the double-ring disk of HD 141569A, using a porous dust model that was previously shown successful in reproducing the spectral energy distributions (SEDs) of the disks around $\beta$ Pictoris and HR 4796A. The dust consists of either unaltered or highly processed interstellar materials and vacuum with a volume fraction of ~90%. Together with a population of polycyclic aromatic hydrocarbon (PAH) molecules of which a large fraction is charged, the porous dust model made of coagulated but otherwise unaltered protostellar interstellar grains provides an excellent fit to the entire SED from the mid-IR to millimeter wavelengths including the PAH mid-IR emission features. The nondetection of the 21 micron crystalline silicate feature predicted from the porous dust model composed of highly-processed grains (mainly crystalline silicate dust) imposes an upper limit of ~10% on the mass fraction of crystalline silicates. Spectroscopic and broadband photometric predictions are made for SIRTF observations which will provide further tests of the applicability of the porous dust model to circumstellar disks.