High helium abundance in the H II region DR-21?

Details High helium abundance in the H II region DR-21? High helium abundance in the H II region DR-21?

Jan 1991

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991pazh...17....3t&link_type=abstract

Pis'ma v Astronomicheskii Zhurnal (ISSN 0320-0108), vol. 17, Jan. 1991, p. 3-15. In Russian. In Russian. In Russian.

Other

Abundance, H Ii Regions, Helium, Interstellar Gas, Radio Spectra, Angular Resolution, Astronomical Models, Ionized Gases, Nebulae, Radio Telescopes

Scientific paper

The 36.5-GHz (H, He) 56 alpha and 22.4-GHz (H, He) 66 alpha radio combination lines were observed in DR-21 on the RT-22 radio telescope. Along with other data, this shows that the measured relative abundance of ionized helium increases with the angular beamwidth, peaking when the beamwidth is 2 - 2.5 arcmin, and then begins to decrease as the angular beamwdith increases further. This behavior is more complicated than previously thought, and can be interpreted as a blister-type nebula model, implying a high actual helium abundance of 26 percent (+ or - 11 percent) in DR-21. By modeling the observed increase in radial velocities of helium lines as the frequency decreases, the gas expansion rate away from the observer can be determined to be 5 - 20 km/s. Possible explanations of this apparently high helium abundance are discussed.

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