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P. D'Alessio (Amer. Museum of Natural History & Inst. de Astronomia, UNAM), N. Calvet, L. Hartmann (Harvard-Smithsonian CfA)
We study the effect of grain growth on the structure, spectral energy distributions (SEDs) and near-IR scattered light images of pre-main sequence \alpha accretion disks, irradiated by their central stars. The disk irradiation, structure and emergent intensity are calculated self-consistently assuming the dust in the disk is composed of spherical grains of silicate and water ice, with different size distributions. For a constant dust to gas mass ratio, increasing the maximum grain radius amax diminishes the opacity in the optical and near-IR range and increases the opacity in the mm range. This means that the opacity to the stellar radiation decreases with increasing amax, decreasing the height of the surface where the largest fraction of the stellar energy is deposited in the disk. The result is that less stellar radiative flux is intercepted, decreasing the far-IR flux emerging from the disk and reducing the range of inclination angles at which the central star is hidden by the disk, in better agreement with the observations. Also, the near-IR scattered light images of edge-on disks become flatter than those predicted assuming ISM dust. The presence of bigger grains explain naturally the flatter slopes and larger optical depth at mm wavelengths implied by observations.