AAS Meeting #193 - Austin, Texas, January 1999
Session 15. Planetary Nebulae
Display, Wednesday, January 6, 1999, 9:20am-6:30pm, Exhibit Hall 1

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[15.06] The Chemical Abundances of Planetary Nebulae in M31's Bulge and Disk

R. Ciardullo (Penn State), G. H. Jacoby (NOAO)

We use slitlet observations from the Kitt Peak 4-m telescope and photo-ionization models to derive the abundances and central star parameters of 12 bulge and 3 disk planetary nebulae (PNe) of M31. As expected, the distribution of abundances in the bulge stars is extremely broad, spanning an entire decade. However, none of the PNe in our sample (or the sample of Stasinska, Richer, & Mc Call 1998) have super metal-rich abundances comparable to that derived for [Fe/H] via absorption line spectroscopy of M31's nucleus. We show that the [O/H] vs.\ [Fe/H] discrepancy could be due to a combination of factors, including an inability of metal-rich stars to produce bright PNe, a luminosity selection effect, and an abundance gradient in the bulge of M31. Additionally, we identify a spatially compact group of 5 PNe which have unusually high O/H; we speculate that this subgroup may arise from a recent merger.

The fact that the brightest [O~III] \lambda 5007 PNe in M31 span nearly a decade in oxygen abundance supports the use of the planetary nebula luminosity function (PNLF) as a standard candle in galaxies of differing metallicities. Moreover, our analysis shows that a statistically significant correlation exists between central star mass and circumstellar extinction. This relationship, which is also present in the PNe of the Magellanic Clouds, is a simple consequence of the greater mass loss and faster evolution times of high mass cores. Because high mass cores (which derive from high mass progenitors) are extincted more than low mass cores, the correlation provides a natural explanation for why the PNe of young stellar systems are no brighter than those associated with old populations. Since real galaxies contain a mix of stellar ages, the relationship also implies that the observed [O~III] \lambda 5007 PNLF of a galaxy will always be dominated by old and intermediate age stars, and thus appear to be independent of population age.

The author(s) of this abstract have provided an email address for comments about the abstract: rbc@astro.psu.edu

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