Dust properties across the CO snowline in the HD 163296 disk from ALMA
  and VLA observations
  To characterize the mechanisms of planet formation it is crucial to
investigate the properties and evolution of protoplanetary disks around young
stars, where the initial conditions for the growth of planets are set. Our goal
is to study grain growth in the disk of the young, intermediate mass star
HD163296 where dust processing has already been observed, and to look for
evidence of growth by ice condensation across the CO snowline, already
identified in this disk with ALMA. Under the hypothesis of optically thin
emission we compare images at different wavelengths from ALMA and VLA to
measure the opacity spectral index across the disk and thus the maximum grain
size. We also use a Bayesian tool based on a two-layer disk model to fit the
observations and constrain the dust surface density. The measurements of the
opacity spectral index indicate the presence of large grains and pebbles
($\geq$1 cm) in the inner regions of the disk (inside $\sim$50 AU) and smaller
grains, consistent with ISM sizes, in the outer disk (beyond 150 AU).
Re-analysing ALMA Band 7 Science Verification data we find (radially)
unresolved excess continuum emission centered near the location of the CO
snowline at $\sim$90 AU. Our analysis suggests a grain size distribution
consistent with an enhanced production of large grains at the CO snowline and
consequent transport to the inner regions. Our results combined with the excess
in infrared scattered light found by Garufi et al. (2014) suggests the presence
of a structure at 90~AU involving the whole vertical extent of the disk. This
could be evidence for small scale processing of dust at the CO snowline.
