The interpretation of recent Crab Nebula filament spectrophotometric observations in the light of detailed photoionization models, indicates that the large measured filament-to-filament variations in the He I 5876 A/H-beta ratio are probably caused by relative He abundance differences. Preliminary evidence suggests an anisotropic distribution of He among the filaments, and that while carbon abundance may be normal, nitrogen, oxygen, neon and sulfur appear to be underabundant by factors of 2-3 in some filaments. The models indicate that the S II forbidden line 6716 A, 6731 A emission is produced in the portion of a given filament that is dominated by H and He atoms, and that the strength of the lines is due to the large volume of such gas in the nebula. A 1.2 solar mass lower limit to the mass of filamentary gas is derived through combination of model results with observations of the total flux of H-beta and forbidden line S II from the Crab Nebula.
No takes yet. Share an insight, caveat, or question.
Henry et al. (1982) studied this question.