EROS: Short period Cepheids in the bar of the LMC.

Abstract

We present Fourier analysis at 490\,nm for 87 Cepheid light curves in the bar of the Large Magellanic Cloud. The photometry has be obtained through the EROS project whose main purpose is the search for baryonic dark matter in the Galactic halo. The very high quality of the photometry and the good phase coverage enable us to obtain accurate Fourier decomposition of the ligh curves. As a consequence we confirm that the so-called s-Cepheids are overtone pulsators and represent about 30 $\%$ of our sample, whereas the Classical Cepheids are fundamental pulsators. We have identified a number of features in plots of amplitude ratios and phase differences versus period. These features are usually related to resonances between different pulsation modes. If we accept that Fourier decomposition techniques applied to light curves yield positions for the centres of resonances, then it seems that resonances occur in LMC Cepheids at the same period as in Galactic Cepheids for fundamental pulsators, whereas they appear to be at shorter periods for overtone pulsators.