Photometry of Emission Lines in Certain Gaseous Nebulae.
Abstract
Photoelectric observations of Ha, Hp, H , and He I X 5876 in the diffuse nebulae NGC 604 (in Messier 33), M8, M20, and the Orion Nebula, and the planetaries IC 3568 and NGC 6543 are presented The question of the optical depth of the nebulae in Ha is discussed, and it is concluded that the hypothesis that the nebulae are optically thin in Ha fits the observations. The helium/hydrogen ratio for each object is determined, and the average is 0.106 by number. There is very remarkable uniformity. The deviations of the He/H ratios of the four diffuse nebulae discussed in this paper are only 6 per cent of the average.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 1962
- DOI:
- 10.1086/147390
- Bibcode:
- 1962ApJ...136..374M