Variable stars in nearby galaxies. VI. Frequency-period distribution of Cepheids in IC 1613 and other galaxies of the Local Group

摘要

The frequency--period distribution and other properties of Cepheids in IC1613 are discussed and compared with those of stars in our Galaxy (Milky Way),LMC, SMC, M31 and M33. Taking into account the observational limitations andrelated incompleteness, it is concluded that the frequency-period distributionof Cepheids in IC 1613 is similar to that of SMC; we suspect that a much largernumber of stars exist in IC 1613 with a period of less than 2 d that have notyet been detected. A discussion of the deficiency of fundamental mode Cepheidswith periods in the range 8 - 10 d in the Milky Way, M31 and M33 is reported.The present data are not sufficient to verify if this is produced by a realbimodal frequency--period distribution or whether depends on the lack ofpulsating stars in such a period range due to pulsational stability reasons.Some arguments are presented in favor of a bimodal distribution that is afunction of the average metallicity. The Milky Way, M31 and M33 have the twomaxima located at the same periods, about 5 and 13 d, respectively. A commenton very long period Cepheids is also given.