A simple model for Cepheid variability.
Abstract
A simple, mathematically tractable onezone model of Cepheid variability is constructed from the well known nonadiabatic equations governing the process. The central feature of this model is that the equation of motion is discontinuous; e. g. the equation of the compression phase differs from that of the expansion phase. (The existence of this discontinuity was deduced from astronomical observations on Cephei.) The difference between the compression and expansion phases is not qualitative but merely quantitative and, mathematically speaking, it may be arbitrarily small; nevertheless, it harbors the mathematical mechanism for the limit cycle. Necessary conditions for the existence of the limit cycle are derived, and the entire theory is applied to (5Cephei. The predicted motion of the model preserves qualitatively and quantitatively that observed on 8 Cephei. Key words: Cepheids  limit cycles
 Publication:

Astronomy and Astrophysics
 Pub Date:
 June 1970
 Bibcode:
 1970A&A.....6..193R