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

Volume 40 number 1 (2012)

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Douglas L. Welch

Department of Physics and Astronomy, McMaster University, Hamilton, ON, L8S 4M1, Canada; welch@physics.mcmaster.ca

Abstract

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.