He-4 determinations from radio recombination lines

Details He-4 determinations from radio recombination lines He-4 determinations from radio recombination lines

Feb 1983

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983prhe.work..281m&link_type=abstract

IN: ESO Workshop on Primordial Helium, Garching, West Germany, February 2, 3, 1983, Proceedings (A83-50030 24-90). Garching, Wes

Physics

2

Abundance, Helium Isotopes, Interstellar Matter, Radio Spectra, Recombination Reactions, Chemical Evolution, Galactic Evolution, H Ii Regions, Line Spectra

Scientific paper

From radio recombination spectra observed in galactic H II regions one can determine the ionic abundances Y+, Y++ of helium and can guess from the "geometrical effect" the fraction of neutral He, Y0, contained within the H+ Strömgren sphere. The authors discuss the results of He recombination line surveys of the northern and southern galactic plane. There appears to exist an observable gradient in the Y+ abundance for galactocentric distances Dg ⪆ 8 kpc, but at smaller values Dg the variation of Y+ is dominated by the amount of neutral He. This effect appears to be caused by a softening of the ionizing radiation with decreasing Dg.

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