A Review of Recent Observations of Dust in H II Regions
The upper limit for the absorption cross section σ H ext , of dust in H II regions in the wavelength range 912−504 Å derived by Mezger et al. (1974), is compatible with that expected for large dust grains, and a gas-to-dust ratio equal to that in the general interstellar medium. The albedo of the small grains must be high for λ > 504 Å. This restriction is lifted if the visual extinction cross section of the grains in H II regions is less than that for grains in the general interstellar medium. New observations of the Orion Nebula indicate that the visual extinction cross section is within a factor 2 of the value in the general interstellar medium.
KeywordsTotal Cross Section Absorption Cross Section Column Density Radio Observation Extinction Cross Section
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