Helium in southern H II regions.
Abstract
Optical and radio observations of the helium abundances in the southern H II regions NGC 3576, RCW 38, and NGC 6357 are discussed. A discrepancy between optical and radio-recombination-line values for N(He+)/N(H+) in the case of NGC 6357 is attributed to the dissimilar observing techniques. One possibility is that the radio observations with bandwidths of about 6 prime are integrating over regions which include much neutral helium, while the optical observations encompass regions of high surface brightness in H beta. Systematic calibration error appears ruled out by the good agreement in the case of NGC 3576.-
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 1974
- DOI:
- 10.1086/153129
- Bibcode:
- 1974ApJ...193...69D
- Keywords:
-
- Abundance;
- Astronomical Spectroscopy;
- Emission Spectra;
- H Ii Regions;
- Helium;
- Balmer Series;
- Cassegrain Optics;
- Electron Density (Concentration);
- H Lines;
- Nebulae;
- Radio Spectra;
- Southern Hemisphere;
- Temperature Measurement;
- Astrophysics