THE LOCAL GROUP DWARF IRREGULAR GALAXY NGC-6822 .1. THE STELLAR CONTENT

We present deep UBVRI CCD photometry of the resolved stellar content o f the Local Group Dwarf Irregular Galaxy NGC 6822. The main advantage of this new data is that the color-magnitude (CM) diagrams obtained co ntain stars of virtually all ages and metallicities and hence are a re cord of the full star formation history of the galaxy. The wide field covered permits unbiased analysis of the whole galaxy. In turn, the la rge number of NGC 6822's measured stars (similar or equal to 18000) en sures that even short-lived stellar evolutionary phases like AGE will be populated by a significant number of stars. A derivation from these data of the full star formation history of the galaxy, using syntheti c CM diagrams, will be presented in two forthcoming papers. In the pre sent paper, we discuss all the preliminary steps to perform that analy sis: we discuss the data, and we present a detailed study of crowding effects on the photometry using artificial stars tests. We show the pr ocess to obtain all the necessary information for the simulation of ob servational effects on the synthetic CM diagrams to produce model CM d iagrams directly comparable with the observed CM diagrams. In addition , a new estimate of distance and reddening using Cepheids is presented and compared with the result for the distance calculated using the ti p of the red giant branch as a distance indicator. A distance modulus of (m - M)(0) = 23.49 +/- 0.08 and a reddening of E(B - V) = 0.24 +/- 0.03 have been obtained. (C) 1996 American Astronomical Society.