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A new exact method for line radiative transfer
Article first published online: 15 DEC 2005
DOI: 10.1111/j.1365-2966.2005.09770.x
Issue
Monthly Notices of the Royal Astronomical Society
Volume 365, Issue 3, pages 779–791, January 2006
Additional Information
How to Cite
Elitzur, M. and Asensio Ramos, A. (2006), A new exact method for line radiative transfer. Monthly Notices of the Royal Astronomical Society, 365: 779–791. doi: 10.1111/j.1365-2966.2005.09770.x
Publication History
- Issue published online: 15 DEC 2005
- Article first published online: 15 DEC 2005
- Accepted 2005 October 11. Received 2005 October 10; in original form 2005 August 8
- Abstract
- Article
- References
- Cited By
Keywords:
- line: formation;
- radiative transfer;
- methods: numerical;
- ISM: lines and bands
ABSTRACT
We present a new method, the coupled escape probability (CEP), for exact calculation of line emission from multi-level systems, solving only algebraic equations for the level populations. The CEP formulation of the classical two-level problem is a set of linear equations, and we uncover an exact analytic expression for the emission from two-level optically thick sources that holds as long as they are in the ‘effectively thin’ regime. In a comparative study of a number of standard problems, the CEP method outperformed the leading line transfer methods by substantial margins.
The algebraic equations employed by our new method are already incorporated in numerous codes based on the escape probability approximation. All that is required for an exact solution with these existing codes is to augment the expression for the escape probability with simple zone-coupling terms. As an application, we find that standard escape probability calculations generally produce the correct cooling emission by the C ii 158-μm line but not by the 3P lines of O i.