Statistics – Computation
Scientific paper
Feb 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...268..617s&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 268, no. 2, p. 617-623.
Statistics
Computation
2
Cepheid Variables, Computational Astrophysics, Numerical Analysis, Radiative Transfer, Stellar Atmospheres, Computerized Simulation, Grid Generation (Mathematics), Perturbation Theory, Stellar Models
Scientific paper
The use of operator perturbation methods such as the Scharmer scheme makes it possible to solve problems involving complex atomic and atmospheric models. In order to take full advantage of these techniques and to guarantee a highly accurate final solution it is imperative to distribute the frequency quadrature points for the radiative error term integrals in a way as to ensure the correct numerical integration with a minimum of computational expense. It is found that in dynamical atmospheres the establishment of a frequency grid meeting this demand is a nontrivial task that necessitates the use of adaptive grids. To this end we investigate various possible explicit frequency grid equations and their numerical properties. We show that there exists at least one grid equation that always leads to better performance than the best fixed grid. Even in highly dynamical Cepheid atmospheres a given accuracy is attained without a costly trial and error procedure, employing a moderate number of quadrature points. In addition, the proposed adaptive grid turns out to be quite inexpensive. We demonstrate its excellent performance in the context of dynamical atmospheres using the six-level Ca II atomic model given by Carlsson (1986).
Moser Georg
Stift Martin J.
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