Type 2 Cepheids in the Milky Way Galaxy and the Magellanic Clouds


Douglas L. Welch

Department of Physics and Astronomy, McMaster University, Hamilton, ON, L8S 4M1, Canada

Invited review paper, received May 10, 2012


Type 2 Cepheids are radially pulsating variable stars that have been recognized as a distinct class for sixty years. As the lower-mass and hence lower-luminosity counterparts of the classical Cepheids, Type 2 Cepheids have attracted less observational and theoretical attention in the intervening decades. Fortunately, the recent availability of long, high-quality photometric time-series has renewed interest in these variables. The results from the OGLE-III surveys of the Large and Small Magellanic Clouds have been particularly exciting, especially with respect to the identification of “peculiar W Virginis” stars which appear to be components of binary systems. It has also become apparent that the sample of Milky Way field Type 2 Cepheids in catalogues is highly contaminated with other classes of variable stars. In this review, I describe important developments in the study of Type 2 Cepheids and suggest research opportunities—many of which do not require the acquisition on new data.