We present a review of the torus radiation transfer and hydrodynamics code. torus uses a 1-D, 2-D or 3-D adaptive mesh refinement scheme to store and manipulate the state variables, and solves the equation of radiative transfer using Monte Carlo techniques. A framework of microphysics modules is described, including atomic and molecular line transport in moving media, dust radiative equilibrium, photoionisation equilibrium, and time-dependent radiative transfer. These modules provide a flexible scheme for producing synthetic observations, either from analytical models or as post-processing of hydrodynamical simulations (both gridbased and Lagrangian). A hydrodynamics module is also presented, which may be used in combination with the radiation-transport modules to perform radiation-hydrodynamics simulations. Benchmarking and validation tests of each major mode of operation are detailed, along with descriptions and performance/scaling tests of the various parallelisation schemes. We give examples the uses of the code in the literature, including applications to low-and high-mass star formation, cluster feedback, and stellar winds, along with an Appendix listing the refereed papers that have used torus.

We present a numerical simulation of the formation of a massive star using MonteCarlo-based radiation hydrodynamics (RHD). The star forms via stochastic disc accretion and produces fast, radiation-driven bipolar cavities. We find that the evolution of the infall rate (considered to be the mass flux across a 1500 au spherical boundary), and the accretion rate onto the protostar, are broadly consistent with observational constraints. After 35 kyr the star has a mass of 25 M and is surrounded by a disc of mass 7 M and 1500 au radius, and we find that the velocity field of the disc is close to Keplerian. Once again these results are consistent with those from recent high-resolution studies of discs around forming massive stars. Synthetic imaging of the RHD model shows good agreement with observations in the near-and far-IR, but may be in conflict with observations that suggests that MYSOs are typically circularly symmetric on the sky at 24.5 µm. Molecular line simulations of a CH 3 CN transition compare well with observations in terms of surface brightness and line width, and indicate that it should be possible to reliably extract the protostellar mass from such observations.