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AN INTERFEROMETER INVESTIGATION OF THE TWENTYONE CENTIMETER HYDROGEN LINE ABSORPTION,
OWENS VALLEY RADIO OBSERVATORY PASADENA CA
The brightness distributions across five intense radio sources were investigated in the hydrogen line absorption features, and the feastures were resolved into Gaussian components. In some cases there was found a variation of the absorption across the face of the source, which, with the kinematical distance to the cloud in question, allowed a typical length to be estimated, which in turn allows estimations of densities and masses. Densities range from a few atoms per cubic centimeter to, in the case of a small cloud in front of Orion A, as much as 680 atoms per cubic centimeter. Masses range from a few solar masses up to perhaps a thousand solar masses in the cloud causing the deep line in Cas A. The absorption features in several other sources were briefly investigated, including three absorption spectra never before published, and new upper limits for the absorption of apparently unabsorbed sources were set in six cases. This material is briefly analyzed statistically, from which it is concluded that the distribution law for central optical depths is approximately e-Tau o, and that a line of sight, on the average, intersects 4.1 clouds per kiloparsec in the galactic plane. There is some evidence that the density is up to twice this in the local spiral arm. Author