The Araucaria Project: The Distance to the Local Group Galaxy NGC 6822 from Cepheid Variables Discovered in a Wide-Field Imaging Survey

We have obtained mosaic images of NGC 6822 in V and I bands on 77 nights. From these data, we have conducted an extensive search for Cepheid variablesover the entire field of the galaxy, and we have found 116 such variables withperiods ranging from 1.7 to 124 days. We used the long-period ($>$ 5.6 days)Cepheids to establish the period-luminosity relations in V, I and in thereddening-independent Wesenheit index, which are all very tightly defined.Fitting the OGLE LMC slopes in the various bands to our data, we have deriveddistance values for NGC 6822 in V, I and ${\rm W}_{\rm I}$ which agree verywell among themselves. Our adopted best distance value from the reddening-freeWesenheit index is 23.34 $\pm$ 0.04 (statistical) $\pm$ 0.05 (systematic) mag.This value agrees within the combined 1 sigma uncertainties with a previousdistance value derived for NGC 6822 by McAlary et al. from near-IR photometryof 9 Cepheids, but our new value is significantly more accurate. We compare theslopes of the Cepheid PL relation in V and I as determined in the fivebest-observed nearby galaxies, which span a metallicity range from -1.0 to -0.3dex, and find the data consistent with no metallicity dependence of the PLrelation slope in this range. Comparing the magnitudes of 10-day Cepheids withthe I-band magnitudes of the TRGB in the same set of galaxies, there is noevidence either for a significant variation of the period-luminosity zeropoints in V and I. The available data limit such a zero point variation to lessthan 0.03 mag, in the considered low-metallicity regime.Comment: Latex, Astronomical Journal accepte