The TORUS radiation transfer code

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 grid-based 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 on 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. (C) 2019 The Authors. Published by Elsevier B.V.