On the Nature of the Cygnus-X Radio Source as Derived from Observations in the Continuum and at the Hydrogen-Line Frequency

Abstract

Continuum emission from the Cygnus-X radio source has been studied at seven frequencies in the range 92 Mc/s to 1425 Mc/s. Its spectrum is that expected from an H II region having a peak emission measure of 6,000 and a constant flux density of |$47\,\times\,{10}^{-24}\,\text w/\text{m}^{2}/\text{c}/\text{s}$| . Evidence is presented which indicates that although its structure is irregular it contains no intense regions of small angular diameter. Measurements taken at the position of Cygnus-X in the 21 cm line of neutral hydrogen show an anomalous “ absorption ” at the frequency characteristic of the second spiral arm in Cygnus. The results can be explained adequately in terms of the conversion of neutral hydrogen at the position of the source to the ionized state. If Cygnus-X is in the second spiral arm at a distance of perhaps 6 Kpc as the “ absorption ” effect suggests, its mass is |${10}^{7}\,\times\text{M}_{\odot}$| . There is a concentration of O- and B- stars in the Cygnus-X region, some of which are contained in a cluster at about 2 Kpc. If these stars were within a spiral arm they could produce a large fraction of the ionization required.