Pakal: A Threedimensional Model to Solve the Radiative Transfer Equation
Abstract
We present a new numerical model called "Pakal" intended to solve the radiative transfer equation in a threedimensional (3D) geometry, using the approximation for a locally planeparallel atmosphere. Pakal uses precalculated radial profiles of density and temperature (based on hydrostatic, hydrodynamic, or MHD models) to compute the emission from 3D source structures with high spatial resolution. Then, Pakal solves the radiative transfer equation in a set of (3D) ray paths, going from the source to the observer. Pakal uses a new algorithm to compute the radiative transfer equation by using an intelligent system consisting of three structures: a cellular automaton; an expert system; and a program coordinator. The code outputs can be either twodimensional maps or onedimensional profiles, which reproduce the observations with high accuracy, giving detailed physical information about the environment where the radiation was generated and/or transmitted. We present the model applied to a 3D solar radial geometry, assuming a locally planeparallel atmosphere, and thermal freefree radio emission from hydrogenhelium gas in thermodynamic equilibrium. We also present the convergence test of the code. We computed the synthetic spectrum of the centimetricmillimetric solar emission and found better agreement with observations (up to 10^{4} K at 20 GHz) than previous models reported in the literature. The stability and convergence test show the high accuracy of the code. Finally, Pakal can improve the integration time by up to an order of magnitude compared against linear integration codes.
 Publication:

The Astrophysical Journal Supplement Series
 Pub Date:
 June 2010
 DOI:
 10.1088/00670049/188/2/437
 arXiv:
 arXiv:1106.2180
 Bibcode:
 2010ApJS..188..437D
 Keywords:

 methods: numerical;
 radiation mechanisms: thermal;
 radiative transfer;
 Sun: atmosphere;
 Sun: chromosphere;
 Sun: radio radiation;
 Astrophysics  Solar and Stellar Astrophysics
 EPrint:
 9 figures