NOAO >   Observing Info >   Approved Programs >   2004A-0059

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Proposal Information for 2004A-0059


PI: Jack Baldwin, Michigan State University, baldwin@pa.msu.edu
Address: Physics Department, 3270 Biomedical Physical Sciences Building, East Lansing, MI 48824, USA

CoI: Robert Williams, Space Telescope Science Institute
CoI: Edward Jenkins, Princeton University

Title: Chemical Abundances in Nebulae: Integrated Absorption and Emission-Line Analysis

Abstract: Serious discrepancies have arisen in CNONe abundances determined from forbidden vs. permitted emission lines for galactic nebulae. The cause of the discrepancies, which can exceed an order of magnitude for some PNe, has been studied intensively, but is still unknown. Emission line abundances cannot be considered reliable until the nature of these contradictory results is understood. We have developed a technique for integrating absorption lines into emission analyses for diffuse nebulae that provides an independent check on the validity of emission-line analyses. It requires high resolution observations of UV resonance absorption produced by the nebular gas in front of embedded or background stars together with forbidden emission line strengths from optical spectra. Such observations currently exist for only one object, IC 418. We have been awarded cycle 12 HST time to obtain UV spectra of four PNe central stars with STIS that will provide data necessary to exploit this new technique. Here we propose for 3 nights of 2.1m time to obtain the necessary ground-based measurements of the strengths of optical-passband emission lines of NGC 6543, the one northern-hemisphere object in this sample. As a secondary program, we will also observe NGC 7027 to calibrate our existing KPNO echelle spectra of this object.


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NOAO >   Observing Info >   Approved Programs >   2004A-0059

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