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The Atmospheres and Spectra of Central Stars

Published online by Cambridge University Press:  14 August 2015

K.H. Böhm
K.H. Böhm*
Affiliation:
University of Heidelberg, Germany

Abstract

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After a brief discussion of the determination of the effective temperature, the surface gravity and the chemical composition of the central stars, we describe the typical problems arising in the computation of static and dynamical models of the very hot atmospheres of these objects. Special attention is paid (1) to the strong non-greyness of the atmosphere, (2) the electron-scattering contribution to the source function, (3) the contribution of the higher ions of C, N, O and Ne to the absorption coefficient, (4) the importance of radiation-pressure effects. The application of the computed energy distribution to the determination of the ionization stratification of the nebula and to the calculation of the bolometric correction is discussed.

A formation of emission edges due to the Schuster effect does not seem to occur in any of the static non-grey model atmospheres which have been computed so far. The reason is that the steep temperature gradient in the uppermost layers of these models strongly favors the formation of absorption edges. Using very simple dynamical models by Schmid-Burgk (1967) we discuss the possibility of a considerable flattening of this temperature gradient by a hydrodynamic outflow driven by radiative acceleration. We argue that the Schuster effect may be much more important, if these atmospheres are not in hydrostatic equilibrium.

The position of central stars of different spectral type in the Teff-g plane is discussed.

Type
Session V – Central Stars
Information
Symposium - International Astronomical Union , Volume 34: Planetary Nebulae , 1968 , pp. 295 - 316
Copyright
Copyright © Reidel 1968 

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