Other
Scientific paper
Dec 1978
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1978apj...226..947k&link_type=abstract
Astrophysical Journal, Part 1, vol. 226, Dec. 15, 1978, p. 947-962.
Other
97
Abundance, Helium Atoms, Hydrogen Atoms, Milky Way Galaxy, Planetary Nebulae, Astronomical Spectroscopy, H Beta Line, Mass Ratios, Neutral Particles, Nuclear Fusion, Optical Thickness
Scientific paper
The origin of the variation of the He/H ratio among planetary nebulae is investigated on the basis of photoelectric observations of 24 nebulae in the He I line at 4471 A, previous observations of 31 nebulae in the He II line at 4686 A, and other earlier studies yielding information on 78 planetaries. H-beta fluxes, forbidden O III (4959 A)/H-beta intensity ratios, and central star magnitudes are obtained for most of the planetaries. He/H ratios are calculated for all nebulae that fulfill certain criteria. An apparent radial gradient in He/H ratio is found, and this apparent gradient is explained in terms of the high proportion of Population II nebulae for galactocentric distances in excess of 12 kpc, helium enrichment of nebulae by fusion processes in the parent stars, and the mass range of stars at the cited distances.
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