Double-Mode Cepheids

Abstract

As their name implies double-mode (or beat) cepheids form a subgroup of cepheid variables which appear to be pulsating simultaneously in two modes. From the period ratio of the two frequencies, the modes have been identified with the fundamental and first overtone modes of radial pulsation. Petersen (1973) was the first to establish that the two periods can be used to determine the masses and radii of these stars independent of any other knowledge such as luminosities, effective temperatures or gravities. The masses derived by this technique are 2 to 3 times lower than the expected evolutionary masses, given that these stars are normal population I cepheids. It is this result that has stimulated much of the subsequent research on double-mode cepheids.