SIMBAD references

The shape of the radial velocity and light curves of 24 long-period (30≤P≤134d) 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 134d. The Fourier parameter-period diagrams for the radial velocity curves show trends which remind in part those of Cepheids with period near 10d. The plausible interpretation is a resonance, probably P₀/P₁=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 .