Abstract
The primary purpose of this paper is to survey at least the author's understanding of the present status of thinking on the basic physical mechanisms which may induce instability in a star against purely radial, infinitely small oscillations. It is generally believed that the pulsations of at least some kinds of real stars owe their origin to such an instability against small oscillations. If a star or stellar model is found to be unstable against very small oscillations, then the oscillations will grow in amplitude until nonlinear processes limit the amplitude to some finite value (see Christy's paper in this Symposium) or until the system disrupts. Such ‘self-excited’ oscillations which have arisen from an instability against infinitesimal oscillations are often called ‘soft’ (cf. Ledoux and Walraven 1958, p. 550), and the system is said to be pulsationally unstable, or overstable in Eddington's terminology. A pulsationally unstable system may be expected to begin pulsating essentially spontaneously since small perturbations are always present. Oscillations whose amplitude can grow only after a finite perturbation has been applied to the system are often called ‘hard’ self-excited oscillations. As has been emphasized by Ledoux and Whitney (1961), the possibility should not be excluded that some kinds of stellar oscillations may be examples of hard self-excited oscillations. We do not, however, discuss this possibility further in this paper.
Publisher
Cambridge University Press (CUP)
Cited by
2 articles.
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1. Giant star seismology;The Astronomy and Astrophysics Review;2017-06-15
2. Observational Techniques for Asteroseismology;Astronomy and Astrophysics Library;2009