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We aim to derive the chemical behavior of a significant sample of PNe and HIIregions in the irregular galaxy NGC 6822 The selected objects are distributedin different zones of the galaxy. Due to the faintness of PNe and HII regionsin NGC 6822, to gather spectroscopic data with large telescopes is necessary.We obtained a well suited sample of spectra by employing VLT-FORS 2 andGemini-GMOS spectrographs. Ionic and total abundances are calculated for theobjects where electron temperatures can be determined through the detection of[OIII] \lambda 4363 or/and [NII] \lambda 5755 lines. A "simple" chemicalevolution model has been developed and the observed data are used to compute amodel for NGC 6822 in order to infer a preliminary chemical history in thisgalaxy. Confident determinations of He, O, N, Ne, S and Ar abundances werederived for a sample of 11 PNe and one HII region. We confirm that the presentISM is chemically homogeneous, at least in the central 2 kpc of the galaxy,showing a value 12+log O/H = 8.06$\pm$0.04. From the abundance pattern of PNe,we identified two populations: a group of young PNe with abundances similar toHII regions and a group of older objects with abundances a factor of two lower.A couple of extreme Type I PNe were found. No third dredge-up O enrichement wasdetected in PNe of this galaxy. The abundance determinations allow us todiscuss the chemical behavior of the present and past ISM in NGC 6822. Ourpreliminary chemical evolution model predicts that an important gas-mass lostoccurred during the first 5.3 Gyr, that no star higher than 40 M$_\odot$ wasformed, and that 1% of all 3-15 M$_\odot$ stars became binary systemsprogenitors to SNIa.

Chemical behavior of the Dwarf Irregular Galaxy NGC 6822. Its PN and HII region abundances