Dust Density Distribution and Imaging Analysis of Different Ice Lines in
  Protoplanetary Disks
  Recent high angular resolution observations of protoplanetary disks at
different wavelengths have revealed several kinds of structures, including
multiple bright and dark rings. Embedded planets are the most used explanation
for such structures, but there are alternative models capable of shaping the
dust in rings as it has been observed. We assume a disk around a Herbig star
and investigate the effect that ice lines have on the dust evolution, following
the growth, fragmentation, and dynamics of multiple dust size particles,
covering from 1 $\mu$m to 2 m sized objects. We use simplified prescriptions of
the fragmentation velocity threshold, which is assumed to change radially at
the location of one, two, or three ice lines. We assume changes at the radial
location of main volatiles, specifically H$_2$O, CO$_2$, and NH$_3$. Radiative
transfer calculations are done using the resulting dust density distributions
in order to compare with current multiwavelength observations. We find that the
structures in the dust density profiles and radial intensities at different
wavelengths strongly depend on the disk viscosity. A clear gap of emission can
be formed between ice lines and be surrounded by ring-like structures, in
particular between the H$_2$O and CO$_2$ (or CO). The gaps are expected to be
shallower and narrower at millimeter emission than at near-infrared, opposite
to model predictions of particle trapping. In our models, the total gas surface
density is not expected to show strong variations, in contrast to other
gap-forming scenarios such as embedded giant planets or radial variations of
the disk viscosity.
