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The Location of the ZZ Ceti Stars on the Hertzsprung-Russell Diagram

Published online by Cambridge University Press:  12 April 2016

John P. Cox  and
Carl J. Hansen
John P. Cox
Affiliation:
Joint Institute for Laboratory Astrophysics* and Department of Physics and Astrophysics, university of Colorado, Boulder, Colorado 80309
Carl J. Hansen
Affiliation:
Joint Institute for Laboratory Astrophysics* and Department of Physics and Astrophysics, university of Colorado, Boulder, Colorado 80309

Abstract

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By means of a simple analysis, it is shown that the combination of long periods and relatively high effective temperatures in ZZ Ceti variables may be made consistent with each other if the driving region for instability occurs at a temperature of (1–2) × 105K. Since this temperature does not coincide with the zone of He+ ionization, the driving mechanism is then not the same as for the Cepheid variables and the linear extension of the Cepheid strip down to the ZZ Ceti white dwarfs may be regarded as a coincidence. A Stelllngwerf “bump” type mechanism may be more appropriate for the latter. However, it is also shown that the short period modes computed by Dziembowski and found to be unstable, are consistent with the Cepheid mechanism. A special plea is made for further opacity calculations at temperatures of ~105 K and densities within a few orders of magnitude of unity — a ρ-T region of considerable interest for the envelopes of ZZ Ceti variables.

Type
Colloquium Session VI
Information
International Astronomical Union Colloquium , Volume 53: White Dwarfs and Variable Degenerate Stars , August 1979 , pp. 392 - 396
Copyright
Copyright © The University of Rochester 1979

References

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