Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 1977
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1977a%26a....58..411p&link_type=abstract
Astronomy and Astrophysics, vol. 58, no. 3, June 1977, p. 411-421. Research supported by the Conselho Nacional de Pesquisa.
Astronomy and Astrophysics
Astrophysics
18
Astronomical Spectroscopy, Emission Spectra, Forbidden Bands, Planetary Nebulae, Abundance, Astronomical Models, Carbon, Electron Density (Concentration), Ionization, Nitrogen, Oxygen, Sulfur
Scientific paper
Schematic two- and three-component models are proposed to account for the forbidden lines due to low- and intermediate-ionization stages of C, N, O, and S observed in the planetary nebula NGC 7027. It is found that the two-component model yields only an approximate solution and that no acceptable solution exists in the framework of the three-component model. An alternative three-component model is suggested in which two shaded regions emit a large fraction of the forbidden lines due to neutral and singly ionized species, high-density cold neutral condensations embedded in a highly ionized lower-density gas produce the shadows, a large fraction of the nebula is at a moderate electron temperature of the order of 10,000 K, and the ionized skin of the condensations is slightly higher. Elemental abundances in the nebula are evaluated.
Aldrovandi M. V. S.
Pequignot Daniel
Stasinska Grazina
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