Three-Dimensional Radiation Transfer in Young Stellar Objects

TL;DR

This paper presents an enhanced 3D dust radiative transfer code for modeling young stellar objects, incorporating complex geometries, emission processes, and external illumination to better understand star formation environments.

Contribution

The authors have upgraded the HOCHUNK3D code to include new emission mechanisms, diverse geometries, dust stratification, and external illumination, enabling more realistic simulations of star-forming regions.

Findings

Outflow cavities may be more clumpy than infalling envelopes.

PAH emission can indicate evolutionary stage better than broadband SED slope.

Externally illuminated clumps can mimic YSOs in observations.

Abstract

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.