2000A&A...356L..37A

The light curves of population I classical Cepheids with period P in the range between 5 and 13 days in the very metal poor irregular galaxy IC 1613 have been analyzed and compared with those of Cepheids in the Galaxy. Even if there are few Cepheids in this period range in IC 1613, the results are of some importance for the (presently unsuccessful) attempts to reproduce the observed light curves with nonlinear models for low metal content Z. Looking at the shape, there is a general similarity of the light curves in both galaxies, even if Z∼0.02 for Galaxy and ∼0.001 for IC 1613, but the same shape occurs in different period ranges. The theoretically predicted sensitivity of Fourier parameters to Z is apparently confirmed just in part by IC 1613 Cepheids, since the observed parameters are compatible with purely radiative model results, but for Z larger than 0.01. A comparison with SMC Cepheids (Z∼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 serious problem than it is presently deemed.