The periodic variables are giant and super-giant stars with periodic variations ranging from an hour or so to three years in length. In spectral class, the stars range from A to M and N (see Stellar Spectra). Those with the longest period have spectra of the latest type and those with the shortest periods tend to be A (or B) stars. Those of longest period are called Long-Period Variables and are red-giant stars. Stars with periods between a day and fifty days or more, the Cepheid Variables, are super-giant stars with spectral types near F or G at maximum. Stars with periods less than a day, called the RR Lyrae Variables, have spectral types between A and F, and absolute magnitudes near zero. Between the long-period variables and the RR Lyrae stars occurs a less well defined series of periodic variables, with giant or super-giant luminosities and spectral types between F And K.

Copyright (c) 1997-99 Michael Erlewine