Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994ap%26ss.220..235m&link_type=abstract
Astrophysics and Space Science (ISSN 0004-640X), vol. 220, no. 2, p. 235-242
Astronomy and Astrophysics
Astrophysics
Absorption, Atmospheric Models, Atomic Energy Levels, Computer Programs, Error Analysis, Opacity, Stellar Atmospheres, Stellar Models, Computerized Simulation, Interpolation, Stellar Temperature
Scientific paper
Different issues involved in the numerical evaluation of continuous absorption by hydrogen-like and ions have been analyzed. Usually, the calculation of the opacity coefficient is explicitly performed for a predetermined number of levels and the higher ones are treated as an integral; it is shown that there are some cases where as many as 17 discrete levels need to be added before switching to the integral approximation if an error smaller than 0.1% is wanted in the results (a condition not always fulfilled with model atmosphere codes being used). Also, approximations to Gaunt factors are analyzed. Though in some cases approximations can be used which are very good, there are other occasions when it should be advisable to switch to interpolating in original tables, or to use more elaborated expressions (such as Hummer's for the Gaunt free-free factor). A numerical procedure for solving the non linear Pg-Pe-T relation is described in an Appendix.
Merlo David C.
Milone Luis A.
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