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Abundances, planetary nebulae, and stellar evolutionAmong Henry Norris Russell's many achievements were his contributions to solar and stellar spectroscopy, in particular, to an analysis of the chemical composition of the solar atmosphere. The question of composition differences between stars was hotly debated; some distinguished astronomers argued that all stars had the solar composition. Some early challenges to this doctrine are described. Determinations of chemical compositions of gaseous nebulae were much more difficult. If we observe the lines of a given chemical element in one ionization stage in a stellar spectrum, we can deduce readily the abundance of that element. No such luxury is available for a planetary or diffuse gaseous nebula. We must measure lines of as many ionization stages as we can. Furthermore, a nebula is an extended object. Often detailed spectroscopy is at hand only for narrow pencil columns taken through the image. Different observers use a variety of apertures. Fortunately it is possible to calculate theoretical spectra for any arbitrary cross section taken through a symmetrical model, so UV, optical, and IR observations all can be compared properly with a prediction. The value of high-resolution spectra obtained with instruments such as the Hamilton Echelle Spectrograph at Lick Observatory is emphasized. Improved fluxes for weak but important transitions are found. Close blends of lines of different ions can be resolved, and checks can be made on predictions of atomic parameters such as Einstein A-values and collision strengths. High spectral resolution data have been obtained and reduced for 22 planetary nebulae of varying size, structure, stellar population membership, dustiness, level of excitation, evolutionary status, and chemical compositions. The promise seems justified that with such extensive, high quality data, additional insights on nebular genesis and late states of stellar evolution can be found. The present survey is confined to nebulae of high surface brightness, but among these are found some engaging objects such as NGC 7027, IC 4997, and NGC 6572.
Document ID
19950039598
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Aller, Lawrence H.
(University of California, Los Angeles, CA United States)
Date Acquired
August 16, 2013
Publication Date
September 10, 1994
Publication Information
Publication: Astrophysical Journal, Part 1
Volume: 432
Issue: 2
ISSN: 0004-637X
Subject Category
Astrophysics
Accession Number
95A71197
Funding Number(s)
CONTRACT_GRANT: NSG5-358
CONTRACT_GRANT: NAG5-1799
CONTRACT_GRANT: NAG5-1207
CONTRACT_GRANT: NSF AST-90-14133
CONTRACT_GRANT: NSF AST-83-12384
CONTRACT_GRANT: NSF AST-87-15514
CONTRACT_GRANT: NAG5-1063
Distribution Limits
Public
Copyright
Other

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