Abstract
THE SPECTRA OF CEPHEID VARIABLES.—The detailed results of an extensive series of spectroscopic observa tions of twcntv Cepheid variables have been published bv Dr. Shapley (Astrophysical Journal, xliv., 273). The data indicate that regular changes in spectral type accompany the periodic variations in light, and constitute one of the general and fundamental proper ties of variable stars of this class. It is somewhat disconcerting to read that, in spite of the great number of observations of the magnitudes of such stars, no really precise information as to maximum r^agnitude and range of variation is yet available. The data, hovvever, are sufficient to show that the earlier spectral types are associated with the shorter periods. Among the twenty, stars in question, the earliest type at maximum is that shown by RS Böotis, which is B8, passing to Fo at minimum. The most advanced type at maximum is shown by U Vulpeculse, which is Fy, and passes to 65 at minimum. The periods of these two stars are respectively 0.377 day and 7.990 days. No Cepheid variable hitherto observed has failed to show variability of the spectrum, and it is probable that all the variables of this class are subject to similar periodic disturbances of the radiating surfaces. Dr. Shapley has previously stated his reasons for re jecting attempted explanations which are based on a supposed binary character of the Cepheid variables, and for regarding the variations as arising from pulsa tions in a single body.
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Our Astronomical Column . Nature 98, 498–499 (1917). https://doi.org/10.1038/098498a0
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DOI: https://doi.org/10.1038/098498a0