Computer Science
Scientific paper
Aug 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999noao.prop..198j&link_type=abstract
NOAO Proposal ID #1999B-0198
Computer Science
Scientific paper
We will observe ~ 50 planetary nebulae (PNe) in the bulge of M31 to derive their chemical compositions. In our 1995 pilot study of 15 PNe in M31's bulge, we found a range of metallicities spanning 1 dex with -1 < [O/H] < 0, with a median value of [O/H] ~ -0.5. This median metallicity is close to the LMC value, although the dispersion in M31 is several times higher. Considering that the integrated stellar spectra in the central bulge/nucleus of M31 exhibits a strong-lined spectrum indicating super- Solar iron and magnesium abundances, the low metallicities of the PNe are surprising. Possible explanations discussed by Jacoby & Ciardullo (1999) include (1) an inability for metal-rich stars to become PNe, (2) a luminosity selection effect (3) an abundance gradient in the bulge, and (4) a non-standard chemical enrichment scenario, which produces [O/Fe] < 0. We wish to extend our observations to examine which of these possibilities are most important. By observing additional PNe with a range of brightnesses, we will be able to directly test the abundance gradient hypothesis, and check whether the large fraction of halo PNe (15%) found by Jacoby & Ciardullo is typical of M31. (If so, it implies that M31's halo is significantly more massive than our own, since we would expect only 1% of the PNe to have halo abundances.) If the trend towards low abundances remains, then we will be forced to conclude that either the abundance patterns of M31's bulge are very different from that of the Galaxy, or that, as suggested by Jacoby et al (1997), stars like the Sun never become bright PNe. We received time in October 1998 to continue this project, but the one good night of data was corrupted by a failure of the atmospheric dispersion corrector. The run was a loss.
Ciardullo Robin
Jacoby George
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