Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 1985
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985a%26a...152..213h&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 152, no. 2, Nov. 1985, p. 213-218. DFG-supported research.
Astronomy and Astrophysics
Astrophysics
27
H Alpha Line, Halos, Oxygen Spectra, Planetary Nebulae, Stellar Winds, Data Reduction, Forbidden Transitions, Line Spectra, Mathematical Models, Ultraviolet Radiation
Scientific paper
Measurements of profiles and intensities of the forbidden O III 5007 A and H-alpha lines emitted by the faint extended halos around the planetary nebulae NGC 6543, NGC 6826, and NGC 7662 are presented. The small widths of the lines indicate radial expansion velocities between 5 and 10 km/s, considerably smaller than those of the central nebulae and compatible with the expected velocity of sound. The surface brightness of the halos are measured to be 1000 to 10,000 times lower than in the main nebulae, implying 100 times lower densities. A model calculation for NGC 6543 shows that the halo line emission can be expected by collisional excitation and radiative recombination following the ionization of the material by the Lyman radiation from the PN nucleus. The filamentary shells surrounding the halos are ionized inner edges of massive cold gas shells formed during the mass loss phase of the PN precursors.
Baessgen Martin
Grewing Michael
Hippelein H. H.
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