The Spectral Energy Distribution of HH 30 IRS: Constraining the Circumstellar Dust Size Distribution

We present spectral energy distribution (SED) models for the edge-onclassical T Tauri star HH30 IRS that indicate dust grains have grown to largerthan 50 microns within its circumstellar disk. The disk geometry andinclination are known from previous modeling of multiwavelength Hubble SpaceTelescope images and we use the SED to constrain the dust size distribution.Model spectra are shown for different circumstellar dust models: a standard ISMmixture and larger grain models. As compared to ISM grains, the larger dustgrain models have a shallower wavelength dependent opacity. Models with thelarger dust grains provide a good match to the currently available data, butmid and far-IR observations are required to more tightly constrain the dustsize distribution. The accretion luminosity in our models is L_acc<0.2 L_starcorresponding to an accretion rate of 4E-9M_sun/yr. Dust size distributionsthat are simple power-law extensions (i.e., no exponential cutoff) yieldacceptable fits to the optical/near-IR but too much emission at mm wavelengthsand require larger disk masses. Such a simple size distribution would not beexpected in an environment such as the disk of HH30 IRS, particularly over sucha large range in grain sizes. However, its ability to adequately characterizethe grain populations may be determined from more complete observationalsampling of the SED in the mid to far-IR.Comment: ApJ Accepte