W Virginis and RV Tauri stars have periods of more than a day to over a hundred days. This group spans the range between the RR Lyrae stars and the long-period variables. These stars all occur in globular clusters (as do the RR Lyrae stars) and are often called Type II Cepheids. They have a spectral class of F to 6, but display strong bright lines of hydrogen. The group of shortest period is called the RV Tauri stars, after a typical specimen while those having periods between ten and thirty days are W Virginis stars. Whereas all the classical Cepheids are found in the galactic plane (within the layer of dust and gas), the type II Cepheids occur at large distances from the plane of the galaxy and form a more nearly spherical system, like that filled by the globular clusters.

Copyright (c) 1997-99 Michael Erlewine