First stellar abundances in NGC 6822 from VLT-UVES and Keck-Hires spectroscopy

We have obtained the first high-resolution spectra of individual stars in t he dwarf irregular galaxy NGC 6822. The spectra of the two A-type supergian ts were obtained at the Very Large Telescope and Keck Observatories, using the Ultraviolet-Visual Echelle Spectrograph and the High Resolution Echelle Spectrometer, respectively. A detailed model atmospheres analysis has been used to determine their atmospheric parameters and elemental abundances. T he mean iron abundance from these two stars is [[Fe/H]] = -0.49 +/- 0.22 (/- 0.21),(6) with Cr yielding a similar underabundance, [[Cr/H]] = -0.50 +/ - 0.20 (+/- 0.16). This confirms that NGC 6822 has a metallicity that is sl ightly higher than that of the SMC and is the first determination of the pr esent-day iron group abundances in NGC 6822. The mean stellar oxygen abunda nce, 12 + log (O/H) = 8.36 +/- 0.19 (+/- 0.21), is in good agreement with t he nebular oxygen results. Oxygen has the same underabundance as iron, [[O/ Fe]] = + 0.02 +/- 0.20 (+/- 0.21). This O/Fe ratio is very similar to that seen in the Magellanic Clouds, which supports the picture that chemical ev olution occurs more slowly in these lower mass galaxies, although the O/Fe ratio is also consistent with that observed in comparatively metal-poor sta rs in the Galactic disk. Combining all of the available abundance observati ons for NGC 6822 shows that there is no trend in abundance with galactocent ric distance. However, a subset of the highest quality data is consistent w ith a radial abundance gradient. More high-quality stellar and nebular obse rvations are needed to confirm this intriguing possibility.