Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1982
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982apj...259..595l&link_type=abstract
Astrophysical Journal, Part 1, vol. 259, Aug. 15, 1982, p. 595-606.
Astronomy and Astrophysics
Astronomy
22
Electron-Ion Recombination, H Ii Regions, Helium Ions, Nebulae, Radio Sources (Astronomy), Abundance, Data Reduction, Gas Ionization, Line Spectra
Scientific paper
High-frequency (10.5 and 14.7 GHz) recombination-line observations of the helium-to-hydrogen ratio in Sgr B2 and seven other bright galactic H II regions have been made. The apparent abundance of singly ionized helium as measured by the radio recombination lines is observed to vary with frequency and from nebula to nebula, but not with the telescope beamwidth. It is proposed that this problem is one of observation and data reduction, and is not a problem in the ionization structure or abundances of nebulae. Systematic errors in the determination of instrumental baselines on the part of all observers, brought on by the presence of impact-boradened line wings and confusing emission in the spectra, can give a frequency dependence in y (the helium-to-hydrogen ratio) and in Delta v(He)/Delta v(H), and can provide the observed correlation between dy/dn (where n is the principal quantum number of the observed transition) and distance from the galactic center.
Brown Raymon L.
Lockman Felix J.
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