Monte Carlo post-processing for radiation hydro simulations of accreting planets in protoplanetary disks

TL;DR

This study compares radiation hydrodynamical simulations with Monte Carlo radiative transfer post-processing to assess temperature distribution accuracy in protoplanetary disks, highlighting discrepancies and pathways for improvement.

Contribution

It provides a detailed comparison between RHD and MCRT methods for temperature estimation in protoplanetary disks, identifying key sources of discrepancies and suggesting improvements.

Findings

High agreement between RHD and MCRT temperatures (~10%)

Largest discrepancies near disk photosphere and outer regions (>40%)

Error in flux estimates quantified for entire disk and accreting planets

Abstract

This paper is part of a series investigating the observational appearance of planets accreting from their nascent protoplanetary disk (PPD). We evaluate the differences between gas temperature distributions determined in our radiation hydrodynamical (RHD) simulations and those recalculated via post-processing with a Monte Carlo (MC) radiative transport (RT) scheme. Our MCRT simulations were performed for global PPD models, each composed of a local 3D high-resolution RHD model embedded in an axisymmetric global disk simulation. We report the level of agreement between the two approaches and point out several caveats that prevent a perfect match between the temperature distributions with our respective methods of choice. Overall, the level of agreement is high, with a typical discrepancy between the RHD and MCRT temperatures of the high-resolution region of only about 10 percent. The largest differences were found close to the disk photosphere, at the transition layer between optically dense and thin regions, as well as in the far-out regions of the PPD, occasionally exceeding values of 40 percent. We identify several reasons for these discrepancies, which are mostly related to general features of typical radiative transfer solvers used in hydrodynamical simulations (angle- and frequency-averaging and ignored scattering) and MCRT methods (ignored internal energy advection and compression and expansion work). This provides a clear pathway to reduce systematic temperature inaccuracies in future works. Based on MCRT simulations, we finally determined the expected error in flux estimates, both for the entire PPD and for planets accreting gas from their ambient disk, independently of the amount of gas piling up in the Hill sphere and the used model resolution.