Dust in the neutral globules of the Helix nebula, NGC 7293

Details Dust in the neutral globules of the Helix nebula, NGC 7293 Dust in the neutral globules of the Helix nebula, NGC 7293

Mar 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992mnras.255..177m&link_type=abstract

Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 255, March 15, 1992, p. 177-182.

Astronomy and Astrophysics

Astronomy

82

Cosmic Dust, Interstellar Matter, Planetary Nebulae, Astronomical Models, Brightness Distribution, Emission Spectra, H Alpha Line, Interstellar Extinction

Scientific paper

Images of the ionized knots and spokes within the helical structure of the Helix nebula are obtained with subarcsecond resolution in the light of the H-alpha + (N II), (O III) 5007 A and (O II) 3727 A emission lines. The (O III) image reveals the knots and their tails in absorption. The globules and tails must be dusty and are seen against the diffuse, central (O III)-emitting volume of the Helix nebula. The curved heads of these neutral knots are radiatively ionized by the light of the central star to produce spatially resolved, bow-shaped H-alpha + (N II) and (O II)-emitting structures displaced (measured for the most prominent globule) by 1.65 arcsec (3.1 x 10 exp 15 cm) towards the central star from the peak of the absorption. Assuming a standard interstellar dust/gas ratio and reddening laws, the total mass in one globule is found to be at least 1.0 x 10 exp -5 solar mass, and the mean gas density is 6.2 x 10 exp 5/cu cm. Considerations on the nature and survival of the globules and their tails are also discussed.

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