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Problems of Gas Dynamics in Planetary Nebulae

Published online by Cambridge University Press:  14 August 2015

F.D. Kahn
F.D. Kahn*
Affiliation:
Dept. of Astronomy, University of Manchester, England

Abstract

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The expansion of a typical planetary nebula is studied by means of a simple model, with spherical symmetry. It is shown that there is a build-up of radiation pressure, due to Lyman-α photons trapped in the nebula, and that this causes the initial acceleration outwards. After some 1·5 × 1011 sec the nebula will have a radius of the order of 1017 cm, and an expansion velocity of about 2 × 106 cm/sec. At roughly this time the dynamical effects of radiation pressure begin to be superseded by those of the recoil pressure at the ionization front, which continues to dominate until the nebula is fully ionized.

Finally some reasons are considered why most nebulae do not have spherically symmetrical shapes, but why so often they appear to be ring-like or butterfly-shaped.

Type
Session IV – Structure and Dynamics
Information
Symposium - International Astronomical Union , Volume 34: Planetary Nebulae , 1968 , pp. 236 - 248
Copyright
Copyright © Reidel 1968 

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