The chemical abundances in a sample of dwarf irregular galaxies I. Small scale variations within NGC 6822?

Deep groundbased spectra of Hubble V and Hubble X, the two largest and brig htest H-II regions in the Local Group dwarf galaxy, NGC 6822. are presented . The extinction, excitation and ionization are studied on scales as small as 4 pc. The chemical composition of some elements within the regions as we ll as possible small scale variations in the abundances of helium, nitrogen , oxygen and neon over the face of the two regions are investigated. The de tection of the emission lines [OI] and [CIIII] are probably related to shoc k-heating from gas ejected from supernova explosions and planetary nebula e jections, respectively, although the contribution to the total ionization i s very small. No significant differences in chemical composition was found between Hubble V and Hubble X. However, some small scale variations in the abundances of oxygen, and possibly nitrogen and helium, over the face of bo th H-II regions were noted, although different physical conditions could ap ply within the regions, such as local fluctuations in the temperature.