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We extended to the R and I bands the light curve coverage for 8 Cepheidsalready studied in B and V by Capaccioli et al [AJ, 103, 1151 (1992)]. Sixteenadditional Cepheid candidates have been identified and preliminary periods areproposed. The new Cepheids allow the period-luminosity relation to be extendedone magnitude fainter. Apparent B, V, R, and I distance moduli have beencalculated. Combining the data at different wavelengths, and assuming a truedistance modulus of 18.50 mag for the LMC, we obtain for NGC 3109 a truedistance modulus $(m-M)_0=25.67\pm0.16$, corresponding to $1.36\pm0.10$ Mpc.Adopting $E(B-V)=0.08$ for the LMC, the interstellar reddening for the Cepheidsin NGC 3109 is consistent with 0. A discussion on the possible implications ofthis result is presented. A comparison of the period-color, period-amplitude,and period-luminosity relations suggests similar properties for the Cepheids inthe LMC, NGC 3109, Sextans A, Sextans B, and IC 1613, though the uncertaintiesin the main parameter determination are still unsatisfactorily high for a firmconclusion on the universality of the period-luminosity relation.Comment: 35 pages, aaspp4.sty, accepted for pubblication on Astron.

On the cepheid variables of nearby galaxies. III. NGC 3109.