The Helium Abundance in the HII Region DR21
The 36. 5-GHz (H, He)56α and 22. 4-GHz (H. HE)66α radio recombination lines have been observed in the DR21 with RT22(FIAN). These data combined with the other show that the measured relative abundance y+ of ionized helium appears to increase with the angular beamwidth, ϕA, peaking at ϕA = 2‘–2. 5‘, and then to decrease as ϕA further increases what is more complicated than in previous papers. This behaviour is interpreted as a blister-type model nebula which implies the high actual helium abundance y0 =(26±11)% in the DR21 and its expansion rate from 5km s-1 to 20km s-1 by approaching the observed increasing of the hydrogen radial velocity with the frequency decreasing. Discussion has concerned slightly the explanation possibilities of the high helium abundance too.
KeywordsAngular Resolution Helium Abundance Radio Recombination Line Measured Relative Abundance Explanation Possibility
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