EROS Variables: Cepheids in the bar of LMC

This also confirms the reality of the colour term in the Cepheid period-luminosity-colour relation. Further, the blue edge of the classical Cepheid instability strip agrees well with the theoretical calculations for the fundamental mode made by Chiosi et al. 1993 (=1993ApJS...86..541C) for the Hertzsprung-Russell and period-luminosity diagrams, but we find that our observed s-Cepheids are >0.2mag brighter and bluer than the Chiosi et al. predictions for the first-overtone.

We identify a number of features in plots of our stars' Fourier-component amplitude ratios and phase differences. These features have been identified with resonances between different pulsation modes. In the LMC we find these features seem to occur at periods very similar to Galactic ones for classical Cepheids, but at different periods for s-Cepheids.

We discover a double-mode Cepheid in the LMC, for which P(first overtone)/P(fundamental)=0.710+/-0.001, very similar to observed ratios for Galactic double-mode Cepheids.