New constraints on dust grain size and distribution in CQ Tau
  Grain growth in circumstellar disks is expected to be the first step towards
the formation of planetary systems. There is now evidence for grain growth in
several disks around young stars. Radially resolved images of grain growth in
circumstellar disks are believed to be a powerful tool to constrain the dust
evolution models and the initial stage for the formation of planets. In this
paper we attempt to provide these constraints for the disk surrounding the
young star CQ Tau. This system was already suggested from previous studies to
host a population of grains grown to large sizes. We present new high angular
resolution (0.3-0.9 arcsec) observations at wavelengths from 850um to 3.6cm
obtained at the SMA, IRAM-PdBI and NRAO-VLA interferometers. We perform a
combined analysis of the spectral energy distribution and of the
high-resolution images at different wavelengths using a model to describe the
dust thermal emission from the circumstellar disk. We include a prescription
for the gas emission from the inner regions of the system. We detect the
presence of evolved dust by constraining the disk averaged dust opacity
coefficient beta (computed between 1.3 and 7mm) to be 0.6+/-0.1. This confirms
the earlier suggestions that the disk contains dust grains grown to significant
sizes and puts this on firmer grounds by tightly constraining the gas
contamination to the observed fluxes at mm-cm wavelengths. We report some
evidence of radial variations in dust properties, but current resolution and
sensitivity are still too low for definitive results.
