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The Observational Properties of the ZZ Ceti Stars

Published online by Cambridge University Press:  12 April 2016

Edward L. Robinson
Edward L. Robinson*
Affiliation:
Department of Astronomy, University of Texas at Austin

Extract

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The ZZ Ceti stars are the pulsating white dwarfs lying within a narrow instability strip, extending in temperature from 13,500 to 10,500 K, on the white dwarf cooling sequence. That white dwarfs should be pulsationally unstable cannot be considered surprising, since theoretical investigations of white dwarf pulsations began at least as early as 1949 (Sauvenier-Goffin 1949). As the predicted pulsation periods demonstrate, however, the nature of the pulsations was not correctly foreseen. With very few exceptions (e.g. Harper and Rose 1970) the early investigations assumed that the most likely pulsations to be excited were radial pulsations. Thus, the calculated periods were quite short, typically 2-10 seconds. The first of the pulsating white dwarfs actually to be observed was HL Tau-76 (Landolt 1968). A portion of its light curve is shown in Figure 1. The typical interval between successive pulses is about 750 seconds, not 2-10 seconds. This is a serious discrepancy, and one that exists for all of the ZZ Ceti stars discovered since HL Tau-76. Clearly, then, the observational data requires us to modify our understanding of pulsating white dwarfs. A considerable body of this observational data now exists. The purpose of the present paper is to present the data, and to show that it provides a reasonably coherent picture of the pulsating white dwarfs.

Type
Colloquium Session VI
Information
International Astronomical Union Colloquium , Volume 53: White Dwarfs and Variable Degenerate Stars , August 1979 , pp. 343 - 358
Copyright
Copyright © The University of Rochester 1979

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