Metallicity effects on the light curve shape of Cepheids with period closeto 10 days

The light curves of population I classical Cepheids with period P in the ra nge between 5 and 13 days in the very metal poor irregular galaxy IC 1613 h ave been analyzed and compared with those of Cepheids in the Galaxy. Even i f there are few Cepheids in this period range in IC 1613, the results are o f some importance for the (presently unsuccessful) attempts to reproduce th e observed light curves with nonlinear models for low metal content Z. Look ing at the shape, there is a general similarity of the light curves in both galaxies, even if Z similar to 0.02 for Galaxy and similar to 0.001 for IC 1613, but the same shape occurs in different period ranges. The theoretica lly predicted sensitivity of Fourier parameters to Z is apparently confirme d just in part by IC 1613 Cepheids, since the observed parameters are compa tible with purely radiative model results, but for Z larger than 0.01. A co mparison with SMC Cepheids (Z similar to 0.005) indicates that the partial compatibility could be just apparent owing to the poor number of stars; if this was true, the failure of nonlinear models would be an even more seriou s problem than it is presently deemed.