The Radio Nebula NRAO 591/593

The radio nebula NRAO 591/593 which appeared to consist of an association of a thermal and non- thermal source, similar to W49, has been observed and analyzed in detail Models have been developed for H ii regions, based on a Gaussian distribution of electron density. The distance has been determined by use of the Maryland-Green Bank 21-Cm Survey. There is no evidence that either of the principal sources is non-thermal, and the physical parameters of the region are derived for comparison with other large H ii regions NRAO 591 contains a small-diameter source with high cutoff frequency, of the type that has been classified as a compact region with high emission measure, but an alternative suggestion is made that compact regions could be non-thermal and could be evidence for the evolution of protostars. Both principal components of the nebula lie below the galactic equator in a region where H i and con- tinuum observations show that the plane is distorted upwar