scholarly journals Monte-Carlo methods for NLTE spectral synthesis of supernovae

2018 ◽  
Vol 620 ◽  
pp. A156 ◽  
Author(s):  
M. Ergon ◽  
C. Fransson ◽  
A. Jerkstrand ◽  
C. Kozma ◽  
M. Kromer ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Radiative Transfer ◽  
Radiation Field ◽  
Spectral Synthesis ◽  
Time Dependent ◽  
Thermal Excitation ◽  
Chain Model ◽  
Full Time ◽  
Emission Frequency ◽  
Radiative Transfer Problem

We present JEKYLL, a new code for modelling of supernova (SN) spectra and lightcurves based on Monte-Carlo (MC) techniques for the radiative transfer. The code assumes spherical symmetry, homologous expansion and steady state for the matter, but is otherwise capable of solving the time-dependent radiative transfer problem in non-local-thermodynamic-equilibrium (NLTE). The method used was introduced in a series of papers by Lucy, but the full time-dependent NLTE capabilities of it have never been tested. Here, we have extended the method to include non-thermal excitation and ionization as well as charge-transfer and two-photon processes. Based on earlier work, the non-thermal rates are calculated by solving the Spencer-Fano equation. Using a method previously developed for the SUMO code, macroscopic mixing of the material is taken into account in a statistical sense. To save computational power a diffusion solver is used in the inner region, where the radiation field may be assumed to be thermalized. In addition, a statistical Markov-chain model is used to sample the emission frequency more efficiently, and we introduce a method to control the sampling of the radiation field, which is used to reduce the noise in the radiation field estimators. Except for a description of JEKYLL, we provide comparisons with the ARTIS, SUMO and CMFGEN codes, which show good agreement in the calculated spectra as well as the state of the gas. In particular, the comparison with CMFGEN, which is similar in terms of physics but uses a different technique, shows that the Lucy method does indeed converge in the time-dependent NLTE case. Finally, as an example of the time-dependent NLTE capabilities of JEKYLL, we present a model of a Type IIb SN, taken from a set of models presented and discussed in detail in an accompanying paper. Based on this model we investigate the effects of NLTE, in particular those arising from non-thermal excitation and ionization, and find strong effects even on the bolometric lightcurve. This highlights the need for full NLTE calculations when simulating the spectra and lightcurves of SNe.

The Solution of Transient Radiative Transfer With Collimated Incident Serial Pulse in a Plane-Parallel Medium by the DRESOR Method

2008 ◽  
Vol 130 (10) ◽  
Author(s):  
Qiang Cheng ◽  
Huai-Chun Zhou ◽  
Zhi-Feng Huang ◽  
Yong-Lin Yu ◽  
De-Xiu Huang
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Method ◽  
Radiative Transfer ◽  
Incident Radiation ◽  
Anisotropic Scattering ◽  
Time Dependent ◽  
Temporal Response ◽  
One Dimensional ◽  
Unit Energy ◽  
The Monte Carlo Method

A time-dependent distribution of ratios of energy scattered by the medium or reflected by the boundary surfaces (DRESOR) method was proposed to solve the transient radiative transfer in a one-dimensional slab. This slab is filled with an absorbing, scattering, and nonemitting medium and exposed to a collimated, incident serial pulse with different pulse shapes and pulse widths. The time-dependent DRESOR values, representing the temporal response of an instantaneous, incident pulse with unit energy and the same incident direction as that for the serial pulse, were proposed and calculated by the Monte Carlo method. The temporal radiative intensity inside the medium with high directional resolution can be obtained from the time-dependent DRESOR values. The transient incident radiation results obtained by the DRESOR method were compared to those obtained with the Monte Carlo method, and good agreements were achieved. Influences of the pulse shape and width, reflectivity of the boundary, scattering albedo, optical thickness, and anisotropic scattering on the transient radiative transfer, especially the temporal response along different directions, were investigated.

A Microstructure-Based Monte Carlo Investigation on the Anisotropic Radiative Transfer in Porous Ceramics

2016 ◽  
Author(s):  
B. X. Wang ◽  
C. Y. Zhao
Keyword(s):  
Monte Carlo ◽  
Radiative Transfer ◽  
Thermal Barrier Coatings ◽  
Gas Turbines ◽  
Radiative Properties ◽  
Thermal Barrier ◽  
Radiative Transfer Problem ◽  
Barrier Coatings ◽  
Aspect Ratios ◽  
Specific Distribution

Thermal barrier coatings provide excellent thermal insulation for metal components of gas turbines. Although the relationships between microstructures and mechanical properties as well as thermal conductivity of various TBCs have been extensively studied, there still exists a deficiency of a full understanding on microstructural-related thermal radiation transport inside them, which becomes more and more crucial for advanced gas turbine applications requiring higher operating temperatures. This study aims at presenting a microstructure-based numerical investigation on radiative transfer in the air plasma sprayed (APS) TBC. In this study, the microstructures of APS TBCs are quantitatively reconstructed based on the Ultra-Small-Angle X-Ray Scattering (USAXS) measurement by the Stony Brook University group, in which the microscale interlamellar pores, intrasplat cracks and globular voids are regarded as oblate spheroids with different sizes and aspect ratios, with a specific distribution of orientations. This is a typical anisotropic medium, in which the physical properties vary with the observing direction. The anisotropic feature of radiative properties including the scattering coefficient and phase function is for the first time demonstrated using the discrete dipole approximation (DDA) method. A modified Monte Carlo method is proposed and implemented to solve the anisotropic radiative transfer problem in such medium. The spectral normal-hemispherical reflectance and transmittance of the coating are thus obtained and further compared with the experimental data from literature as well as our group to validate this numerical method. This work provides a versatile numerical framework for the study of the anisotropic radiative transfer mechanism in APS thermal barrier coatings based on microstructure charaterization.

scholarly journals Circumstellar H2O in M-type AGB stars

2008 ◽  
Vol 4 (S251) ◽  
pp. 163-164
Author(s):  
Matthias Maercker ◽  
Fredrik L. Schöier ◽  
Hans Olofsson
Keyword(s):  
Radiative Transfer ◽  
Radiation Field ◽  
Central Star ◽  
Thermal Excitation ◽  
Circumstellar Envelope ◽  
Agb Stars ◽  
Dust Grains ◽  
Transfer Modelling

AbstractSurprisingly high amounts of H2O have recently been reported in the circumstellar envelope around the M-type AGB star W Hya. However, substantial uncertainties remain, as the required radiative transfer modelling is difficult due to high optical depths, sub-thermal excitation and the sensitivity to the combined radiation field from the central star and dust grains.

scholarly journals High-resolution, 3D radiative transfer modelling

2020 ◽  
Vol 643 ◽  
pp. A90
Author(s):  
Angelos Nersesian ◽  
Sébastien Viaene ◽  
Ilse De Looze ◽  
Maarten Baes ◽  
Emmanuel M. Xilouris ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Radiative Transfer ◽  
Radiation Field ◽  
Stellar Population ◽  
Spectral Energy Distribution ◽  
Stellar Populations ◽  
Infrared Emission ◽  
Spectral Energy ◽  
Combined System ◽  
Energy Fraction

Context. Investigating the dust heating mechanisms in galaxies provides a deeper understanding of how the internal energy balance drives their evolution. Over the last decade radiative transfer simulations based on the Monte Carlo method have emphasised the role of the various stellar populations heating the diffuse dust. Beyond the expected heating through ongoing star formation, older stellar populations (≥8 Gyr) and even active galactic nuclei can both contribute energy to the infrared emission of diffuse dust. Aims. In this particular study we examine how the radiation of an external heating source, such as the less massive galaxy NGC 5195 in the M 51 interacting system, could affect the heating of the diffuse dust of its parent galaxy NGC 5194, and vice versa. Our goal is to quantify the exchange of energy between the two galaxies by mapping the 3D distribution of their radiation field. Methods. We used SKIRT, a state-of-the-art 3D Monte Carlo radiative transfer code, to construct the 3D model of the radiation field of M 51, following the methodology defined in the DustPedia framework. In the interest of modelling, the assumed centre-to-centre distance separation between the two galaxies is ∼10 kpc. Results. Our model is able to reproduce the global spectral energy distribution of the system, and it matches the resolved optical and infrared images fairly well. In total, 40.7% of the intrinsic stellar radiation of the combined system is absorbed by dust. Furthermore, we quantify the contribution of the various dust heating sources in the system, and find that the young stellar population of NGC 5194 is the predominant dust-heating agent, with a global heating fraction of 71.2%. Another 23% is provided by the older stellar population of the same galaxy, while the remaining 5.8% has its origin in NGC 5195. Locally, we find that the regions of NGC 5194 closer to NGC 5195 are significantly affected by the radiation field of the latter, with the absorbed energy fraction rising up to 38%. The contribution of NGC 5195 remains under the percentage level in the outskirts of the disc of NGC 5194. This is the first time that the heating of the diffuse dust by a companion galaxy is quantified in a nearby interacting system.

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