The possible effects of an unusual resonance in very long period Cepheids

Abstract

The shape of the radial velocity and light curves of 24 long-period (30 < P < 134 days) Cepheids in the Magellanic Clouds shows a progression with the period. The sequences of the radial velocity and light curves are based only on a small sample of stars; however, evident changes of the shape can be seen in Cepheids with period between 90 and 134 d. The Fourier parameter-period diagrams for the radial velocity curves show trends which remind in part those of Cepheids with period near 10 d. The plausible interpretation is a resonance, probably P_0/P_1=2 between the fundamental and the first overtone mode. The possible importance of this phenomenon for the study of stellar structure and evolution in relatively far galaxies is emphasized.

arXiv comment4 pages, latex, 2 figures, A&A, letter in press