The Araucaria Project: A Wide‐Field Photometric Survey for Cepheid Variables in NGC 3109

We have obtained mosaic images of NGC 3109 in the V and I bands on 74 nights,spanning approximately one year. From these data, we have conducted anextensive search for Cepheid variables over the entire field of the galaxy,resulting in the discovery of 113 variables with periods ranging from 3.4 to31.4 days. In this sample, 76 Cepheids, including many long-period variables,were not known before. For the previously known 45 Cepheids in this galaxy, ourdata proved that reported periods were wrong for 14 objects; for nearly allother previously known Cepheid variables we were able to significantly improveon the periods. We construct period-luminosity relations from our data andobtain reddening-corrected distance moduli of 25.72 $\pm$ 0.05 mag in V, and25.66 $\pm$ 0.04 mag in I. The distance modulus derived form thereddening-independent V-I Wesenheit index turns out to be significantly shorter(25.54 $\pm$ 0.05 mag), which indicates that in addition to the foregroundextinction of E(B-V) = 0.05 mag, there is an intrinsic to NGC 3109 redening ofabout 0.05 mag. Our distance obtained based on the reddening-free Wesenheitmagnitudes is consistent with earlier distance determinations of NGC 3109 fromCepheids, and the tip of the red giant branch. We will improve on our distanceand extinction determination combining our optical data with the follow-upnear-infrared observations of a subsample of NGC 3109 Cepheids.Comment: accepted to be published in the Ap