Chemical abundances in planetary nebulae in NGG 6822
Kirsch, Russell Gary
Dufour, Reginald J.
Master of Science
The results of an investigation of the optical spectra of five planetary nebulae and two H II regions are presented. The nebulae, located in NGC 6822, a Local Group Irregular Galaxy at a distance of .557 Mpcs, were examined using the Richey-Cretien spectrograph and the Silicon Intensified (SIT) Vidicon, on the 4-meter telescope at the Cerro Tololo Interamerican Observatory. From the measurement of selected emission line strengths in the XX37 - XX71 spectral ranges, the relative abundances of He, N, , Ne, S are calculated with respect to H (Log (H) = 12.) for each nebula. Electron densities are derived for the planetary nebulae from the ratio of the Cs IlU line intensities, I(6716)/I(6731), while their temperatures are obtained from theiatio of the Co IIlH line intensities, 1(4363), 1(4959), 1(57). The derived chemical abundances are examined in the context of possible Nitrogen enrichment of the Interstellar Medium and the possible age of the galaxy. Type I planetaries exhibited a He and N enrichment of factors of up to 2 and 31, respectively. The high N enrichment indicates it is a product of Primary Nucleosynthesis, and Type I planetaries are probably significant in N enrichment of the ISM. Type II planetaries exhibit a He and N enrichment of a lesser magnitude than Type I; factors of 1.4 and 5, respectively. This lower enrichment indicates N is a product of Secondary Nucleosynthesis. The age of NGC 6822 is probably similar to that of the Milky Way Galaxy, about 1^1 years, whereas the Magellanic Clouds are younger, a few 1^9 years.