Research Papers in Physics and Astronomy


Date of this Version


Document Type



Bulletin of the American Astronomical Society, Vol. 12 (1980), p. 862


Copyright 1980 American Astronomical Society.


Fourier decompositions are made for~ number of observed velocity curves of classical Cepheids. The observations are fit with Fourier series of the form

vobs = A0 - Ai sin(iwt + ϕi) ,

where the index i runs from 1 to 4 or 1 to 8 depending upon the requirements of the data. Although the sample of stars is small, we show that the Hertzsprung progression expresses itself quantitatively in terms of the low-order Fourier coefficients, particularly the quantity ϕ21 = ϕ2 - 2ϕ1. This result complements a similar finding for the light curves. When the Fourier decompositions of the velocity curves are compared with those of some theoretical models (Vermury and Stothers 1978, Ap. J. 225, 939), new evidence is uncovered favoring a resonance explanation for the "bump" sequence.