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Manuscript Title: Computation of line and continuum radiation from thermal radioastronomical sources.
Authors: M. Brocklehurst, M. Salem
Program title: RCMBLN
Catalogue identifier: AAEG_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 9(1975)258
Programming language: Fortran.
Computer: IBM 360/65.
Operating system: OS.
RAM: 25K words
Word size: 32
Peripherals: magnetic tape, disc.
Keywords: Astrophysics, Radioastronomy, Hii region, Thermal source, Radio recombination line, Continuum spectrum.
Classification: 1.4.

Subprograms used:
Cat Id Title Reference

Nature of problem:
The interpretation of radio recombination lines is of importance to radio astronomy. The computer program described in this paper calculates the intensities and profiles of hydrogen and helium radio recombination lines emitted by a thermal source. The electron temperature is assumed to be constant throughout the source,while the electron density is a known function of position. Spherical or plane parallel symmetry is assumed in the program. The theory of the method used is described in detail by Brocklehurst and Seaton. The construction of a spherical model of a thermal radio source, given the radio flux density spectrum, has been described by Salem and Seaton and Salem, and a computer program which carries out the model construction has been written. The model produced can be used as input to the present program.

Solution method:
Atomic hydrogen energy level populations have been computed by Brocklehurst for different values of electron temperature, Te, and electron density, Ne, in the form of coefficients of departure from thermodynamic equilibrium, bn. As the coefficients of absorption and emission depend upon the bn factors, the equation of radiative transfer can be solved numerically for any given distribution of Te and Ne.

The electron temperature is assumed to be constant throughout the source, and clumping is not taken into account. The equation of radiative transfer has been linearized by assuming that, for all lines the optical depth due to line absorption (positive or negative) is much less, in absolute value, than unity; and that the line emissivity is much less than the continuum emissivity at the same frequency. These assumptions are adequate to within the accuracy of present day observations.

Running time:
The running time depends greatly upon the number of points at which Ne is specified. For 33 points, the running time is of the order of 2 s per line of a spherical model on an IBM 360/65 computer. Compilation time is approximatley 20 s.