Observations of [S IV] 10.5 micron and [Ne II] 12.8 micron in Two Halo Planetary Nebulae: Implications for Chemical Self-Enrichment

Details Observations of [S IV] 10.5 micron and [Ne II] 12.8 micron in Two Halo Planetary Nebulae: Implications for Chemical Self-Enrichment Observations of [S IV] 10.5 micron and [Ne II] 12.8 micron in Two Halo Planetary Nebulae: Implications for Chemical Self-Enrichment

2002-10-15

arxiv.org/abs/astro-ph/0210356v2

Astron.J.125:265,2003

Astronomy and Astrophysics

Astrophysics

accepted by AJ; 27 pages, 2 postscript figures; typo in abstract corrected

Scientific paper

10.1086/345572

We have detected the [S IV] 10.5 micron and [Ne II] 12.8 micron fine-structure lines in the halo population planetary nebula (PN) DdDm 1, and set upper limits on their intensities in the halo PN H 4-1. We also present new measurements of optical lines from various ions of S, Ne, O, and H for DdDm 1, based on a high-dispersion spectrum covering the spectral range 3800 A to 1 micron. These nebulae have similar O/H abundances, (O/H) = 1e-4, but S/H and Ne/H are about half an order of magnitude lower in H 4-1 than in DdDm 1; thus H 4-1 appears to belong to a more metal-poor population. This supports previous suggestions that PNe arising from metal-poor progenitor stars can have elevated oxygen abundances due to internal nucleosynthesis and convective dredge-up. It is generally accepted that high abundances of carbon in many PNe results from self-enrichment. To the extent that oxygen can also be affected, the use of nebular O/H values to infer the overall metallicity of a parent stellar population (for example, in external galaxies) may be suspect, particularly for low metallicities.

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