THE SPECTRAL ENERGY DISTRIBUTION OF HH 30 IRS: CONSTRAINING THE CIRCUMSTELLAR DUST SIZE DISTRIBUTION

We present spectral energy distribution (SED) models for the edge-on classical T Tauri star HH 30 IRS that indicate that dust grains have grown to larger than 50 km within its circumstellar disk. The disk geometry and inclination are known from previous modeling of multiwavelength Hubble Space Telescope images, and we use the SED (0.5 km j 3 mm) to constrain the dust size distribution. Model spectra are shown for dierent circumstellar dust models: a standard interstellar medium (ISM) mixture and larger grain models. As compared to ISM grains, the larger dust grain models have a shal-lower wavelength-dependent opacity: smaller at short wavelengths and larger at long wavelengths. Models with the larger dust grains provide a good match to the observed SED of HH 30 IRS. Although the currently available SED is poorly sampled, we estimate and aL B 0.2 L _, MdiskB 1.5] 10~3 M_,power law with exponential cuto dust grain size distribution. This model provides a good Ðt to the currently available data, but mid- and far-IR observations are required to more tightly constrain the size distribution. The accretion luminosity in our models is corresponding to an accretion rateL acc [ 0.2L *,yr~1. Dust size distributions that are simple power-law extensions (i.e., no exponen-M0 [ 4] 10~9 M _tial cuto) yield acceptable Ðts to the optical/near-IR but too much emission at millimeter wavelengths