The Spatial Homogeneity of Nebular and Stellar Oxygen Abundances in the Local Group Dwarf Irregular Galaxy NGC 6822

To test the existence of a possible radial gradient in oxygen abundanceswithin the Local Group dwarf irregular galaxy NGC 6822, we have obtainedoptical spectra of 19 nebulae with the EFOSC2 spectrograph on the 3.6-mtelescope at ESO La Silla. The extent of the measured nebulae spansgalactocentric radii in the range between 0.05 kpc and 2 kpc (over fourexponential scale lengths). In five H II regions (Hubble I, Hubble V, Kalpha,Kbeta, KD28e), the temperature-sensitive [O III] 4363 emission line wasdetected, and direct oxygen abundances were derived. Oxygen abundances for theremaining H II regions were derived using bright-line methods. The oxygenabundances for three A-type supergiant stars are slightly higher than nebularvalues at comparable radii. Linear least-square fits to various subsets ofabundance data were obtained. When all of the measured nebulae are included, noclear signature is found for an abundance gradient. A fit to only newlyobserved H II regions with [O III] 4363 detections yields an oxygen abundancegradient of -0.14 +/- 0.07 dex/kpc. The gradient becomes slightly moresignificant (-0.16 +/- 0.05 dex/kpc) when three additional H II regions with [OIII] 4363 measurements from the literature are added. Assuming no abundancegradient, we derive a mean nebular oxygen abundance 12+log(O/H) = 8.11 +/- 0.10from [O III] 4363 detections in the five H II regions from our present data;this mean value corresponds to [O/H] = -0.55.