  Rings and asymmetries in protoplanetary disks are considered as signposts of
ongoing planet formation. In this work, we conduct three-dimensional radiative
transfer simulations to model the intriguing disk around HD 143006 that has
three dust rings and a bright arc. A complex geometric configuration, with a
misaligned inner disk, is assumed to account for the asymmetric structures. The
two-dimensional surface density is constructed by iteratively fitting the ALMA
data. We find that the dust temperature displays a notable discontinuity at the
boundary of the misalignment. The ring masses range from 0.6 to 16Mearth that
are systematically lower than those inferred in the younger HL Tau disk. The
arc occupies nearly 20% of the total dust mass. Such a high mass fraction of
dust grains concentrated in a local region is consistent with the mechanism of
dust trapping into vortices. Assuming a gas-to-dust mass ratio of 30 that is
constant throughout the disk, the dense and cold arc is close to the threshold
of being gravitationally unstable, with the Toomre parameter Q~1.3.
Nevertheless, our estimate of Q relies on the assumption for the unknown
gas-to-dust mass ratio. Adopting a lower gas-to-dust mass ratio would increase
the inferred Q value. Follow-up high resolution observations of dust and gas
lines are needed to clarify the origin of the substructures.
