Evidence Favoring Nonevolutionary Cepheid Masses

Abstract

It is suggested that the bumps on the velocity curves of nonlinear Cepheid models may be understood as the consequence of a resonance between the fundamental and the second overtone modes of the pulsating star. Thus the presence of bumps can be inferred from linear calculations. The region of the observational instability strip containing bumps is compared with the location of the calculated resonances. As was the case for the nonlinear calculations, it is found that masses considerably less than evolutionary values are required to bring agreement between the observations and the theory. (AIP)