On the light curve shape of Cepheids in IC 1613 and NGC 6822

INAF-Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy e-mail: elio@merate.mi.astro.it

Received: 12 September 2005
Accepted: 12 December 2005

Abstract

Comparison of the Fourier parameters of fundamental mode Cepheids with period near 10 d in galaxies of the Local Group (IC 1613, NGC 6822, Milky Way, Magellanic Clouds) confirms the previous indication of the lack of a spread of values in some dwarf irregular galaxies. It is not yet clear whether this is a real effect or if it is just due to the low number of Cepheids in these galaxies. We suspect however that in this period range the Cepheids of IC 1613 and NGC 6822 behave differently from those in the Milky Way and the Magellanic Clouds. The main effect of the different metallicity on the Fourier parameters is confirmed to be the larger R₂₁ values of shorter period Cepheids in metal-poorer galaxies. However the metallicity alone should not be enough to explain the various differences among the Cepheids of the four galaxies. The difference between the spread of values near 10 d in Milky Way and Magellanic clouds is pointed out.