An algorithm for Monte Carlo time-dependent radiation transfer

• Published in: Monthly notices of the Royal Astronomical Society Vol. 416; no. 2; pp. 1500 - 1508
• Main Author: Harries, Tim J.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 11.09.2011; Wiley-Blackwell; Oxford University Press
• Subjects: Accretion disks; Algorithms; Astronomy; Astrophysics; Earth, ocean, space; Exact sciences and technology; Local thermodynamic equilibrium; Luminosity; Mathematical analysis; methods: numerical; Monte Carlo methods; Monte Carlo simulation; protoplanetary discs; Protostars; Radiative transfer; Spectral energy distribution; stars: pre-main-sequence; Thermodynamics; protoplanetary discs; stars: pre-main-sequence; methods: numerical; radiative transfer; Accretion; Variability; Spectral energy distribution; Luminosity; Numerical method; Protostars; Algorithms; Radiative transfer; Circumstellar disks; Diffusion; LTE
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1111/j.1365-2966.2011.19147.x

A new Monte Carlo algorithm for calculating time-dependent radiative transfer under the assumption of local thermodynamic equilibrium is presented. Unlike flux-limited diffusion, the method is polychromatic, includes scattering, and is able to treat the optically-thick and free-streaming regimes simultaneously. The algorithm is tested on a variety of 1D and 2D problems, and good agreement with benchmark solutions is found. The method is used to calculate the time-varying spectral energy distribution from a circumstellar disc illuminated by a protostar whose accretion luminosity is varying. It is shown that the time-lag between the optical variability and the infrared variability results from a combination of the photon traveltime and the thermal response in the disc, and that the lag is an approximately linear function of wavelength.