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4 Discussion

In Tables 4 and 5, we derive oxygen abundances for approximately half of the planetary nebulae we observed. For the rest, we derive lower limits. Many of the oxygen abundance limits, however, are very useful. Six of the fourteen temperature limits in Table 5 are below 104K, and one is even below 9000K. If we separate the planetary nebulae in Table 5 on the basis of whether they have temperatures or temperature limits, the mean oxygen abundances of the two sets differ at the 92% confidence level, with the set of objects with temperature limits having a higher mean oxygen abundance by at least 0.11dex. Table 5 shows clearly that we are able to measure oxygen abundances up to approximately the solar value ($12+\log(\mathrm{O}/\mathrm{H})=8.93$dex; Anders & Grevesse 1989). Since the Loral3 CCD has only modest sensitivity at [O III]$\lambda$4363, the quantum efficiency being about 22%, these results are by no means the limit of what is possible with 4m-class telescopes.

In several companion papers, we shall exploit the spectroscopic observations of planetary nebulae in M 32 and in the bulge of M 31 in several ways. First, we intend to study the evolution of the planetary nebulae in these galaxies relative to those in the Milky Way and the Magellanic Clouds. We also intend to investigate the chemical evolution of M 32 and the bulges of M 31 and the Milky Way individually as well as the chemical evolution of DHGs as a class.

Acknowledgements

We would like to thank George Jacoby for making several very helpful comments concerning a preliminary version of this paper, and for making further helpful suggestions as referee. MGR would like to thank the Natural Sciences and Engineering Research Council of Canada and Marshall McCall for their financial support while this research was being done. MGR also thanks the Physics and Astronomy Department at York University for its hospitality and computing facilities while this work was being finished. MLM thanks the Natural Sciences and Engineering Research Council of Canada for its continuing support.


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