The Double-Mode Cepheids

Abstract

AbstractRecent observations of double-mode Cepheids and proposed candidates are reviewed. It appears that the change of modal content reported in some stars may not be real. Observations show that the double-mode Cepheids are indistinguishable from normal Cepheids of similar period. This poses a severe problem for pulsation theory which predicts very low masses from the ratio of first overtone to fundamental period. Attempts to resolve this problem and the problem of modal selection are discussed.