Progress towards a 3D Monte Carlo radiative transfer code for outflow wind modelling

TL;DR

This paper introduces a new 3D Monte Carlo radiative transfer code designed to model inhomogeneous stellar outflows, enabling more accurate simulations of plasma ionization, excitation, and photon-matter interactions in complex geometries.

Contribution

The paper presents the development and testing of a novel 3D Monte Carlo radiative transfer code that handles inhomogeneities and implements photon-matter coupling using macroatom methods.

Findings

The code accurately models 3D radiative transfer in stellar outflows.

Adaptive and regular grids were tested for efficiency and accuracy.

Test results agree with existing Monte Carlo codes, validating the approach.

Abstract

Context: Radiative transfer modelling of expanding stellar envelopes is an important task in their analysis. To account for inhomogeneities and deviations from spherical symmetry, it is necessary to develop a 3D approach to radiative transfer modelling. Aims: We present a 3D Monte Carlo code for radiative transfer modelling, which is aimed to calculate the plasma ionisation and excitation state with the statistical equilibrium equations, moreover, to implement photon-matter coupling. As a first step, we present our Monte Carlo radiation transfer routines developed and tested from scratch. Methods: The background model atmosphere (the temperature, density, and velocity structure) can use an arbitrary grid referred to as the model grid (modGrid). The radiative transfer was solved using the Monte Carlo method in a Cartesian grid, referred to as the propagation grid (propgrid). This Cartesian grid was created based on the structure of the modgrid; correspondence between these two grids was set at the beginning of the calculations and then kept fixed. The propgrid can be either regular or adaptive; two modes of adaptive grids were tested. The accuracy and calculation speed for different propgrids was analysed. Photon interaction with matter was handled using the Lucy's macroatom approach. Test calculations using our code were compared with the results obtained by a different Monte Carlo radiative transfer code. Results: Our method and the related code for the 3D radiative transfer using the Monte Carlo and macroatom methods offer an accurate and reliable solution for the radiative transfer problem, and are especially promising for the inclusion and treatment of 3D inhomogeneities.