The Araucaria Project: The Distance to the Sculptor Group Galaxy NGC 247 from Cepheid Variables Discovered in a Wide-Field

Abstract

We report on the discovery of a Cepheid population in the Sculptor Group spiral galaxy NGC 247 for the first time. On the basis of wide-field images collected in photometric surveys in V and I bands which were conducted with three different telescopes and cameras, 23 Cepheid variables were discovered with periods ranging from 17 to 131 days. We have constructed the period-luminosity relations from these data and obtain distance moduli to NGC 247 of 28.20 $\pm$ 0.05 mag (internal error) in V, 28.04 $\pm$ 0.06 mag in I, and 27.80 $\pm$ 0.09 mag in the reddening-independent Wesenheit index. From our optical data we have determined the total mean reddening of the Cepheids in NGC 247 as E(B-V)=0.13 mag, which brings the true distance modulus determinations from the V and I bands into excellent agreement with the distance determination in the Wesenheit index. The best estimate for the true distance modulus of NGC 247 from our optical Cepheid photometry is 27.80 $\pm$0.09 (internal error) $\pm$ 0.09 mag (systematic error) which is in excellent agreement with other recent distance determinations for NGC 247 from the Tip of the Red Giant branch method, and from the Tully-Fisher relation. The distance for NGC 247 places this galaxy at twice the distance of two other Sculptor Group galaxies, NGC 300 and NGC 55, yielding supporting evidence for the filament-like structure of this group of galaxies. The reported distance value is tied to an assumed LMC distance modulus of 18.50 mag.