Variable stars in nearby galaxies II. Population I and II Cepheids in Field A of IC 1613

The light curves of Cepheids and other variable stars in Field A of IC 1613 , obtained with a CCD and no filter (Wh photometry), have been analyzed. It is possible to separate first overtone from fundamental mode population I Cepheids taking into account the pulsation amplitude, the shape of the ligh t curve and the period. The expected separation is verified in the period-l uminosity PL diagram. Light curve Fourier parameters have been compared wit h those of Magellanic Clouds and galactic Cepheids, in order to point out t he effects of the very low metallicity of IC 1613 on the light curve shape. Population II Cepheids of IC 1613 can be discriminated from those of popula tion I in the PL diagram, and, taking into account their color, from other red or blue variables. Their PL relation is consistent with that observed i n globular clusters, nearby dwarf spheroidal galaxies and LMC. We have show n it is possible to apply the single-phase method for deriving standard pho tometry PL relations for population I and II Cepheids; therefore with just one accurate BVRI observation it is possible to use the population I Cephei ds for distance determinations. Some unusual stars have been identified on the basis of periods, light curv e shapes and colors; they appear to be pulsating stars laying on the extens ion of PL relation of known anomalous Cepheids. A firmer classification of these and other faint stars requires further deeper multicolor observations .