The Orion A helium abundance

Details The Orion A helium abundance The Orion A helium abundance

Dec 1986

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986pazh...12..848t&link_type=abstract

(Pis'ma v Astronomicheskii Zhurnal, vol. 12, Nov. 1986, p. 848-856) Soviet Astronomy Letters (ISSN 0360-0327), vol. 12, Nov.-Dec

Astronomy and Astrophysics

Astronomy

1

Absorption Spectra, Abundance, Helium Ions, Orion Constellation, Astronomical Models, Data Processing, Radial Distribution

Scientific paper

H, He 66α (22.4 GHz) and H, He 56α (36.5 GHz) recombination line observations were made at several positions of the central region of Orion A (R ≈ 3arcmin). The observed relative helium abundance y' is found to increase with the angular distance from the nebular centre and to amount the mean value of 11.6% at the peripherical positions. The comparison with the results of low-frequency observations (H, He 109α, ν ≈ 5.0 GHz) shows that the measurements towards the centre (y' = 8 - 9%) are in agreement with the low-frequency measurements of y', however y' at the peripherical positions are higher than that at low frequency. A nebula model of "blister" type is constructed to explain such behaviour. Conclusions are made that the actual helium abundance y in Orion A is ≈12%, the Orion Nebula expands and its LRS velocity is ≈5 km/s.

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