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J. K. J. Fogel (Harvard University), G. H. Jacoby (WIYN Observatory), R. A. Shaw (NOAO), L. Stanghellini (STScI), G. C. Van de Steene (Royal Obs. Belgium), M. Dopita (MSSSO)
By measuring the abundances in nebulae, and distinguishing the enrichment of processed elements (primarily He, C, N, and O) from non-processed elements, (chiefly Ar, Ne, S) we are able to probe both the chemical enrichment around the planetary nebula and the population type of the progenitor star. Where we can also determine the evolutionary state, and therefore the mass, of the central star, we can also determine the time since the progenitor was formed. Because of these useful properties, studies of 18 PNs in the Large Magellanic Cloud (LMC) and six PNs in the Galactic bulge were undertaken to investigate the stellar population and PN properties in these contrasting environments. We also have spectra for eight more PN of sufficient quality to perform this analysis on them for a total of 14 planetaries out of the ~95 new PN identified by Jacoby & Van de Steene. Neither of these sets of planetaries had been studied before because of the observational difficulties in obtaining high quality data. For the PNs in the Galactic center, the high extinction made it difficult to obtain the traditional optical diagnostic lines; while the study of LMC PNs required the high spatial resolution of HST to resolve the nebular structure.
Moderate-dispersion spectra from MSSSO and spectral images from HST/STIS were used to examine in more detail the results of Stanghellini et al. (2000), where chemical enrichments were found in asymmetric PNs, relative to round or elliptical PNs. For the LMC planetaries, where we observed many diagnostic lines, it was straightforward to create models that matched the observed quantities very well, which then yielded a direct determination of the chemical abundances. Moderate dispersion spectra of the Galactic center PNs yielded far fewer measurable emission lines, and required extensive modeling using Gary Ferland's CLOUDY code to determine the chemical abundances.
Jeffrey Fogel's research was supported by the NOAO/KPNO Research Experiences for Undergraduates (REU) Program which is funded by the National Science Foundation.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.