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Long-Period Variables and Planetary Nebulae

  • Donald H. Menzel (a1)

Abstract

The occasional appearance of a red giant or long-period variable in planetary nebulae poses a problem for theoretical astrophysics. Such a cool nuclear star would not ordinarily provide a source of ultraviolet radiation necessary for the excitation of the spectrum of a gaseous nebula.

One possible solution of this problem postulates the existence of intense magnetic fields in the star. Second, the star itself has a structure resembling that of a miniature, highly compressed planetary, with a high-temperature nuclear star at the centre and a distended atmospheric shell enveloping chiefly the stellar equator.

The magnetic field induces a sort of pumping action that creates the tire-shaped envelope from matter ejected near the poles. As this shell grows denser, it radiates like a stellar photosphere at low temperature. Eventually the shell becomes unstable and disperses outward to form and maintain the nebula. A quasi-periodic situation occurs, which explains the variation of light. Ultraviolet light absorbed during the minima, when the shell has vanished, adequately accounts for the nebular excitation. A wide variety of such symbiotic stars occurs, including repeating novae as well as the long-period variables.

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Copyright

References

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Menzel, D.H. (1946) Physica, 12, 768.
Menzel, D.H. (1968) in the present volume, p. 279.
Menzel, D.H., Shore, B.W. (1966) in Comitato Nazionale per le Manifestazioni Celebrative del IV Centenario della Nascità di Galileo Galilei, Ed. by Barbera, G.
Sargent, W.L.W. (1966) Q. J. R. astr. Soc., 7, 222.

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