Physical conditions and structure in NGC 7293, 'The Helix'

Details Physical conditions and structure in NGC 7293, 'The Helix' Physical conditions and structure in NGC 7293, 'The Helix'

Jun 1975

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1975apj...198..593w&link_type=abstract

Astrophysical Journal, vol. 198, June 15, 1975, pt. 1, p. 593-595, 597, 599-603.

Astronomy and Astrophysics

Astrophysics

27

Astronomical Photography, Galactic Structure, Planetary Nebulae, Astrophysics, Interstellar Extinction, Milky Way Galaxy, Optical Filters

Scientific paper

Results are presented for analyses of image-tube interference filter photographs and spectra of the 'Helix' planetary nebula, NGC 7293. Extinction values as well as electron densities and temperatures are derived for 12 points in the central region and the bright SW filament. Temperatures derived from N II forbidden line/H-alpha ratio are found to be higher than expected if efficient cooling by forbidden radiation occurs in this object. Variations in electron density within the SW filamentary zone are discussed, and variable extinction across the face of the nebula is noted. It is concluded that the structure of NGC 7293 probably consists of two or three rings of low-ionization material surrounding a zone of higher ionization and that a true helical interpretation is probably not realistic.

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