Other
Scientific paper
Jun 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005sptz.prop20049k&link_type=abstract
Spitzer Proposal ID #20049
Other
Scientific paper
The chemical history of the Galactic halo, currently poorly understood, is a critical piece in the puzzle of understanding how the Milky Way and other spiral galaxies have formed and evolved. Stellar spectroscopy studies of halo stars have revealed large abundance variations, sparking various speculations to explain the observed scatter. Halo planetary nebulae (PNe) offer a complementary and independent method of assessing halo chemical composition. The goal of this project is to derive accurate chemical abundances for six halo PNe, including two with extremely interesting abundance profiles, and in so doing, to help evaluate theories of Galactic halo formation and enrichment already motivated by the stellar abundance studies. We propose to obtain IRS spectra of six halo PNe from 6-36 microns to detect emission lines of important elements (including Ne, S and Ar) arising from ionization states that are difficult or impossible to observe from the ground. We will explore the implications of inaccuracies that result from the current necessary practice of applying an empirical "ionization correction factor" to account for the contribution from unobserved ions. Results from the proposed observations, combined with our ground-based spectroscopy already in hand, will lead to: 1) improved understanding of what is necessary for accurate determination of abundances in PNe, particularly for Ne, Ar and S, and 2) deeper insight into the complex pattern of chemical elements in the halo already seen to be exhibited by stars.
Dufour Reginald James
Henry Richard B. C.
Kwitter Karen B.
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