The characteristics of second-overtone-mode Cepheids predicted by non-linear pulsation models

Abstract

Non-linear pulsation models of second-overtone-mode Cepheids have been constructed to study the theoretical characteristics of these hypothetical stars which could lead to observational criteria for their identification. The main results of this work are: (1) the light and velocity curves are similar in part to those of first-overtone Cepheid models; (2) the curves are modulated by the resonance between the second- and the sixth-overtone modes, P 2 /P 6 = 2; (3) observed stars should have smaller amplitudes than those of first-overtone s-Cepheids by a factor ∼1.6, and should have more symmetric light curves; (4) observed Fourier parameter-period diagrams should be similar to those of first-overtone Cepheids but with the observed resonance ‘centre’ at P ∼ 1 d; the true position, however, should be a function of the mass-luminosity relation. Since second-overtone-mode Cepheids may exist in Magellanic Clouds, they could be identified with a certain confidence level by considering their position both in the P – L diagram and in the Fourier parameter diagrams.