Three-dimensional dust radiative-transfer models: the Pinwheel Nebula of WR 104

Abstract

We present radiative‐transfer modelling of the dusty spiral Pinwheel Nebula observed around the Wolf–Rayet/OB‐star binary WR 104. The models are based on the three‐dimensional radiative‐transfer code torus, modified to include an adaptive mesh that allows us to adequately resolve both the inner spiral turns (subau scales) and the outer regions of the nebula (distances of 104 au from the central source). The spiral model provides a good fit to both the spectral energy distribution and Keck aperture masking interferometry, reproducing both the maximum entropy recovered images and the visibility curves. We deduce a dust creation rate of 8 ± 1 × 10−7 M⊙ yr−1, corresponding to approximately 2 per cent by mass of the carbon produced by the Wolf–Rayet star. Simultaneous modelling of the imaging and spectral data enables us to constrain both the opening angle of the wind–wind collision interface and the dust grain size. We conclude that the dust grains in the inner part of the Pinwheel Nebula are small (∼100 Å), in agreement with theoretical predictions, although we cannot rule out the presence of larger grains (∼1 μm) further from the central binary. The opening angle of the wind–wind collision interface appears to be about 40°, in broad agreement with the wind parameters estimated for the central binary. We discuss the success and deficiencies of the model, and the likely benefits of applying similar techniques to the more complex nebulae observed around other WR/O star binaries.

Hierarchical octree andk-d tree grids for 3D radiative transfer simulations

“…The vast majority of these codes are based on Monte Carlo techniques (e.g. Gordon et al 2001;Wolf 2003;Harries et al 2004;Pinte et al 2006;Jonsson 2006;Bianchi 2008;Baes et al 2011;Robitaille 2011;Whitney et al 2013) or ray tracing mechanisms (e.g. Xilouris et al 1997;Steinacker et al 2006).…”

“…In particular, hierarchical octree grids, in which nodes are recursively partitioned into eight subnodes, are a popular choice (e.g. Kurosawa & Hillier 2001;Wolf 2003;Harries et al 2004;Jonsson 2006;Bianchi 2008;Niccolini & Alcolea 2006;Robitaille 2011).…”

Radiation-hydrodynamical simulations of massive star formation using Monte Carlo radiative transfer – II. The formation of a 25 solar-mass star

“…We direct the reader to the first paper in this series (Harries 2015) for a detailed description of the numerical methods used to solve the RHD equations. We emphasise that we have extensively tested and benchmarked the MC RT scheme against dust continuum benchmarks (Harries et al 2004;Pinte et al 2009) and H ii region models Bisbas et al 2015) as well as time-dependent heat-transfer benchmarks Harries (2011). We have also tested the coupled radiationhydrodynamics scheme against the usual 1-D benchmarks, such as the Sod shock tube, the expansion of an H ii region (Harries 2015;Haworth et al 2015), and radiationdriven shell tests (Harries 2015).…”

“…We employ the torus radiation hydrodynamics code (Harries 2000; Harries et al 2004;Harries 2011Harries , 2015 which uses a MC based treatment of the radiation field coupled with an adaptive mesh hydrodynamics scheme and a Lagrangian sink particle implementation. We direct the reader to the first paper in this series (Harries 2015) for a detailed description of the numerical methods used to solve the RHD equations.…”

“…Dedicated RT codes such as cloudy (Ferland et al 2013) manage this, as do a large number of Monte Carlo (MC) based codes (Bjorkman & Wood 2001;Harries et al 2004;Wood et al 2004;Ercolano et al 2005;Pinte et al 2006;Robitaille 2011), but these are usually perceived to be too slow to be useful as the radiation step in an RHD code. However the MC method has one distinct advantage: photon packets are independent.…”