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Manuscript Title: A program to calculate coronal emission line strengths.
Authors: P.L. Dufton
Program title: AATWAB
Catalogue identifier: ACXE_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 13(1977)25
Programming language: Fortran.
Computer: ICL 1906S.
Operating system: GEORGE 4.
RAM: 47K words
Word size: 24
Peripherals: disc.
Keywords: Astrophysics, Plasma physics, Solar corona, Atomic process, Emission line, Excitation rate, Level population, Optically thin.
Classification: 1.6, 19.1.

Nature of problem:
This computer program is used to calculate the intensities of emission spectral lines from the upper solar atmosphere. The optically thin approximation is used and the validity of this assumption is checked by calculating line centre optical depths. Account may be taken of collisional transitions (by electron and proton impact) and spontaneous radiative transitions between all the selected levels of the chosen ion in calculating the intensities. The program integrates these intensities through whatever model atmosphere is selected. The calculation may be done for any position on the solar disk with the assumption of spherical symmetry for the atmosphere.

Solution method:
Steady-state rate equations are set up and then inverted to yield level populations for the ion under consideration. These level populations lead directly to emission line strengths for an optically thin plasma. For a model calculation this process is repeated at each depth point and the emission line strengths integrated over depth to yield total specfic intensities.

Up to 50 levels can be incorporated into the model atom with each fine structure level being counted separately and up to 100 individual transitions and 10 mutliplets included in the emission line strength calculations. If a depth dependent model is being considered a maximum of 101 depth points can be used.

Running time:
Running time is proportional to the square of the number of levels in the model atom and to the number of depth points in the coronal model. The test run took 40 sec on the ICL 1906S.