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| MOCASSIN | |
|---|---|
| Name | MOCASSIN |
| Programming language | Fortran, C |
| Operating system | Unix-like, Linux, macOS |
| Genre | Radiative transfer, Photoionization |
MOCASSIN MOCASSIN is a three-dimensional Monte Carlo photoionization and radiative transfer code used in astrophysics for modeling ionized nebulae, dusty plasmas, and irradiated circumstellar environments. It integrates Monte Carlo methods, atomic data, and dust physics to simulate emission-line spectra and spectral energy distributions for complex geometries often encountered in planetary nebulae, H II regions, and protoplanetary disks. The code has been applied in studies associated with observational programs and missions such as Hubble Space Telescope, Spitzer Space Telescope, Chandra X-ray Observatory, Very Large Telescope, and ALMA.
MOCASSIN implements a three-dimensional Monte Carlo radiative transfer algorithm to solve coupled photoionization and thermal balance problems for gas and dust in astrophysical objects like Orion Nebula, Ring Nebula, Eta Carinae, NGC 7027, and NGC 6302. The code uses atomic and molecular datasets comparable to those in projects like the CHIANTI database, NIST, Opacities Project, and IRAF-era line lists to predict emission from ions such as O III, N II, S II, Ne II, and molecules traced by CO, H2, SiO, and PAH features. Its design parallels Monte Carlo radiative transfer initiatives exemplified by codes like Cloudy, TORUS, RADMC-3D, MAPPINGS, and CLOUDY collaborators.
MOCASSIN was developed in the early 2000s by researchers working at institutions including University College London, University of St Andrews, Queen's University Belfast, University of Manchester, and collaborators linked to observatories such as European Southern Observatory and Royal Observatory Edinburgh. Early releases responded to demands from projects including ISO (Infrared Space Observatory), IRAS, and later to data from Spitzer Space Telescope and Herschel Space Observatory. Development drew on numerical methods from pioneers such as Monte Carlo method applications in radiative transfer championed by groups around Cambridge University, Princeton University, and Max Planck Institute for Astrophysics.
MOCASSIN's architecture couples Monte Carlo photon packet propagation with iterative solvers for ionization and thermal equilibrium, inspired by techniques used in studies associated with Rayleigh scattering and Mie theory implementations used by groups at MPIA and Caltech. It supports multiple dust grain species (e.g., silicates, carbonaceous grains, PAHs) similar to inputs used in Draine and Li models, and uses collisionally-excited line emissivities comparable to datasets from CHIANTI and ADAS. Parallelization approaches reflect practices used on HPC facilities like UK National Supercomputing Service, NERSC, and Leibniz Supercomputing Centre, enabling applications to spatially resolved targets such as protoplanetary disks around objects like HL Tauri and resolved H II regions in galaxies like M33 and M51.
MOCASSIN has been used to model planetary nebulae including NGC 6543, NGC 7009, and to interpret mid-infrared observations of dusty objects such as IRC+10216 and VY Canis Majoris. Studies using MOCASSIN informed analyses of abundance discrepancy problems linked to work on Recombination lines and Collisionally-excited lines discussed in literature from groups at Instituto de Astrofísica de Canarias and INAF. The code supports multi-wavelength comparisons to instruments like JWST, Keck Observatory, Subaru Telescope, Gemini Observatory, and radio arrays like VLA.
Validation efforts compared MOCASSIN outcomes with other community codes such as Cloudy, MAPPINGS V, CLOUDY-based benchmarks, and Monte Carlo codes like TORUS and RADMC-3D. Benchmarking studies were performed against canonical test cases like the Lexington/Meudon photoionization benchmarks and datasets used in workshops at IoA Cambridge, STScI, and international conferences organized by IAU commissions. Results were published in journals such as Monthly Notices of the Royal Astronomical Society, Astronomy & Astrophysics, and The Astrophysical Journal.
MOCASSIN distributions were historically hosted by university groups and released to the community for academic use, with source code written in Fortran and C and parallelized via MPI libraries akin to implementations used at CERN and NERSC. Licensing terms typically reflected academic research use policies similar to those of other community astrophysical codes maintained by institutions like STScI and CfA; users often contact lead developers at associated institutions for access and collaboration.
Notable applications include 3D photoionization modeling of NGC 7027 to reproduce observed infrared line strengths from ISO and Spitzer, dust radiative transfer studies of NGC 6302 comparing to Herschel photometry, and investigations of abundance discrepancies in planetary nebulae reported in works from groups at University of Manchester, University of St Andrews, and University College London. MOCASSIN-based analyses contributed to interpretations of spatially resolved spectroscopy obtained with instruments such as MUSE, SINFONI, and ISAAC, and informed theoretical studies connected to stellar evolution models from groups at Geneva Observatory and Padova Observatory.
Category:Astrophysics software