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Astron. Astrophys. 325, 1132-1150 (1997)

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Time dependent ionization calculations of gaseous nebulae

H. , Marten * 1, R. and Szczerba 2, 3

1 Astrophysikalisches Institut Potsdam, Telegrafenberg A 27, D-14473 Potsdam, Germany
2 N. Copernicus Astronomical Center, Rabianska 8, PL-87100 Toru, Poland
3 Department of Physics and Astronomy, University of Calgary, Calgary, AB T2N 1N4, Canada

Received 22 April 1995 / Accepted 24 February 1997

Abstract

We developed a new computer code which is able to treat the time dependent photo- and collisional ionization of gaseous nebulae together with the consistent energy balance for arbitrary numbers of elements, ions and line transitions. The intention of this paper is to describe the basic numerical methods and a few test calculations as being parts of full spherically symmetric radiation-gasdynamic computations in the limit of a non-moving gas ([FORMULA] = 0). Exemplarily we discuss the evolution of ionization fronts around a suddenly switched-on/switched-off central star with [FORMULA] = 50 000 K and [FORMULA] = 6000 [FORMULA]. Evidence is presented that the photon velocities must artificially be limited in time dependent astrophysical calculations when the equation of radiative transfer is not explicitely treated in a time dependent way. Furthermore, computations with different spatial resolutions demonstrate that a careful choice of the grid resolution in ionization calculations is essential for the interpretation of observed line intensities.

Key words: hydrodynamics – radiative transfer – ISM: general – (ISM:) Hii regions – (ISM:) planetary nebulae: general – ISM: supernova remnants

* present adress: Forschungszentrum Karlsruhe GmbH, Institut für Neutronenphysik und Reaktortechnik, Postfach 3640, D-76021 Karlsruhe, Germany

Send offprint requests to: R. Szczerba, E-mail: szczerba@ncac.torun.pl

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© European Southern Observatory (ESO) 1997

Online publication: April 28, 1998

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