Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 1977
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1977a%26a....54..765c&link_type=abstract
Astronomy and Astrophysics, vol. 54, no. 3, Feb. 1977, p. 765-769.
Astronomy and Astrophysics
Astronomy
12
Atomic Recombination, Hydrogen Recombinations, Line Spectra, Microwave Spectra, Radio Astronomy, Radio Sources (Astronomy), Carbon, Continuous Radiation, H Lines, Helium, Microwave Emission, Radiant Flux Density
Scientific paper
The paper gives the results of recombination line observations of NGC 2024 (Ori B) performed at 5 GHz, 8 GHz, and 10 GHz. Hydrogen and helium emission were measured at 5 and 10 GHz; carbon emission was measured at all three frequencies, and heavier-than-carbon emission was detected at 8 GHz. The ratio of He to H integrated line intensities is 0.018 and 0.015 at 5 and 10 GHz respectively, both accurate within 0.01. The observed He recombination rate is smaller than that predicted, unless the effective temperature of Ori B is below 35,000 K, but a main sequence star at such temperatures would fail to account for the required H-Lyman flux. It is proposed that the exciting star is, indeed, a main sequence star, but the presence of dust enhances the discrepancy between line and continuum radiation. The intensity of the carbon line suggests inefficient conversion of stellar photons into carbon ionizations. Dust could account for the absorption of stellar photons if the density of the C II region is greater than roughly 100,000 per cu cm.
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