Dust growth and setting in protoplanetary disks and radiative transfer calculations

We produced the spectral energy distribution (SED) and the millimetre intensity images of laminar disks by means of radiative transfer calculations to evaluate how the dust growth and settling affect the observed results. We examined two cases at t=4300 and 25 000 yrs, when a dust dominant layer forms at the radial positions of 5.2 AU and 30 AU, respectively. In these regions, the dust particles grow ~6 cm and ~250μm in the dust dominant layers with a geometrical thickness of 1.5×10−5 and 0.016 times the gas scale height. The SED shows a shallow flux slope in the millimetre wavelengths, which is due to thermal emission from submillimetre-sized dust in the several tens AU region. In face-on cases, a triangle-shaped emission feature is also detected in 10μm, which is attributed to small (≲micron-sized) silicate dust floating at the disk surface. In the millimetre intensity images, the dust dominant layer is traced with the thermal emission from the large particles. The spatial distribution of large grains is seen in the image of dlogIν/dlogν−2, which corresponds to a spectral opacity index. The value is low as <2 towards the dust dominant layer, even if the optical depth is low. Although detailed analyses are essential to estimate the physical parameters such as the particle sizes and the dust density distribution, we expect that the evidence for the dust growth and settling is obtained from the real observed data.