Three-Dimensional Radiation Transfer in Young Stellar Objects
  We have updated our publicly available dust radiative transfer code
(HOCHUNK3D) to include new emission processes and various 3-D geometries
appropriate for forming stars. The 3-D geometries include warps and spirals in
disks, accretion hotspots on the central star, fractal clumping density
enhancements, and misaligned inner disks. Additional axisymmetric (2-D)
features include gaps in disks and envelopes, "puffed-up inner rims" in disks,
multiple bipolar cavity walls, and iteration of disk vertical structure
assuming hydrostatic equilibrium. We include the option for simple power-law
envelope geometry, which combined with fractal clumping, and bipolar cavities,
can be used to model evolved stars as well as protostars. We include
non-thermal emission from PAHs and very small grains, and external illumination
from the interstellar radiation field. The grid structure was modified to allow
multiple dust species in each cell; based on this, a simple prescription is
implemented to model dust stratification.
  We describe these features in detail, and show example calculations of each.
Some of the more interesting results include the following: 1) Outflow cavities
may be more clumpy than infalling envelopes. 2) PAH emission in high-mass stars
may be a better indicator of evolutionary stage than the broadband SED slope;
and related to this, 3) externally illuminated clumps and high-mass stars in
optically thin clouds can masquerade as YSOs. 4) Our hydrostatic equilibrium
models suggest that dust settling is likely ubiquitous in T Tauri disks, in
agreement with previous observations.
