Fast and accurate frequency-dependent radiation transport for hydrodynamics simulations in massive star formation

Abstract

Context. Radiative feedback plays a crucial role in the formation of massive stars. The implementation of a fast and accurate description of the proceeding thermodynamics in pre-stellar cores and evolving accretion disks is therefore a main effort in current hydrodynamics simulations. Aims. We introduce our newly implemented three-dimensional frequency dependent radiation transport algorithm for hydrodynamics simulations of spatial configurations with a dominant central source. Methods. The module combines the advantage of the speed of an approximate flux limited diffusion (FLD) solver in the onetemperature approach, which is valid in the static diffusion limit, with the high accuracy of a frequency dependent first order raytracing routine. The ray-tracing routine especially compensates the introduced inaccuracies by standard approximate FLD solvers in transition regions from optically thin to thick and yields the correct optical depths for the frequency dependent stellar irradiation. Both components of our module make use of realistic tabulated dust opacities. The module is parallelized for distributed memory machines based on the message passing interface standard. We implemented the module in the three-dimensional high-order magnetohydrodynamics code Pluto. Results. We prove the viability of the scheme in a standard radiation benchmark test compared to a full frequency dependent MonteCarlo based radiative transfer code. The setup includes a central star, a circumstellar flared disk, as well as an envelope. The test is performed for different optical depths. Considering the frequency dependence of the stellar irradiation, the temperature distributions can be described precisely in the optically thin, thick, and irradiated transition regions. Resulting radiative forces onto dust grains are reproduced with high accuracy. The achievable parallel speedup of the method imposes no restriction on further radiative (magneto-) hydrodynamics simulations. Conclusions. The proposed approximate radiation transport method enables frequency dependent radiation hydrodynamics studies of the evolution of pre-stellar cores and circumstellar accretion disks around an evolving massive star in a highly efficient and accurate manner.

On the stability of radiation-pressure-dominated cavities

“…Ray-tracing + flux-limited diffusion For simulations labeled "RT+FLD", we use our hybrid radiation transport module (see Kuiper et al 2010b). The total radiation energy density F tot is divided into the flux F * (ν, r) of the frequency-dependent stellar irradiation and the flux of the frequency-averaged thermal radiation energy density F…”

“…We introduced the derivation of the solving algorithm as well as its numerical implementation into a three-dimensional (3D) (magneto-)hydrodynamics code in Kuiper et al (2010b). The solver algorithm superposes two radiation fields: a frequency-dependent ray-tracing (RT) component representing the stellar irradiation field and a frequencyaveraged (gray) flux-limited diffusion (FLD) component representing the thermal dust emission.…”

Star Formation with Adaptive Mesh Refinement Radiation Hydrodynamics

“…However, once this radiation is absorbed, following its re-emission with characteristics becomes unreasonably expensive, and a moment method is a far better choice. The underlying idea of a hybrid method, first used in multidimensional simulations by Murray et al (1994) and recently implemented in the Pluto code (Kuiper et al 2010), is to use characteristics for the "first absorption", then switch to a moment method. One does this by performing a characteristic trace from the star or stars to determine the rate of energy and momentum input into each cell by direct radiation.…”

“…Enzo is an open source AMR HD code (an MHD version exists but is not public) with cosmology capabilities and two different radiation methods (Abel & Wandelt 2002;Norman et al 2008;Reynolds et al 2009). Pluto is an open source AMR MHD code with a newly-developed radiation solver (Mignone et al 2007;Kuiper et al 2010). There are also a number of fixed, nested grid codes in use, but I will not mention these by name.…”

The role of accretion disks in the formation of massive stars

“…The evolution of the gas density, velocity, pressure, and total energy density is computed using the magneto-hydrodynamics code Pluto3 (Mignone et al 2007), including full tensor viscosity. The derivation and numerical details of the newly developed frequency dependent hybrid radiation transport method are summarized by Kuiper et al (2010a). Our implementation of Poisson's equation as well as the description of the dust and stellar evolution model are given in Kuiper et al (2010b).…”