Computer Science
Scientific paper
Jan 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993pnas...90..413h&link_type=abstract
Proceedings of the National Academy of Sciences of the United States of America, Volume 90, Issue 2, pp. 413-417
Computer Science
4
Scientific paper
Observations of two dense compact planetary nebulae secured with the Hamilton Echelle spectrograph at Lick Observatory combined with previously published UV spectra secured with the International Ultraviolet Explorer enable us to probe the electron densities and temperatures (plasma diagnostics) and ionic concentrations in these objects. The diagnostic diagrams show that no homogenous model will work for these nebulae. NGC 6572 may consist of an inner torordal ring of density 25,000 atoms/cm^3 and an outer conical shell of density 10,000 atoms/cm^3. The simplest model of IC 4997 suggests a thick inner shell with a density of about 10^7 atoms/cm^3 and an outer envelope of density 10,000 atoms/cm^3. The abundances of all elements heavier than He appear to be less than the solar values in NGC 6572, whereas He, C, N, and O may be more abundant in IC 4997 than in the sun. IC 4997 presents puzzling problems.
Aller Lawrence H.
Hyung Siek
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