Intensities of Discrete Radio Sources in Cygnus and Cassiopeia at 22.6 Mc.s.

Abstract

IT is important both for the understanding of the nature of the localized radio sources and the determination of interstellar radio absorption to extend the measurement of the spectra of the sources to as low radio-frequencies as possible. Ionospheric transmission sets a limit, but by choosing frequencies not too close to the critical frequency, and restricting observations to days of low ionospheric disturbance, reasonably accurate measurements may be obtained. In this way, we have recently made measurements at a frequency of 22.6 Mc./s. (λ = 13.3.m.) by means of an interferometer consisting of two aerials spaced in the east–west direction at 20 wave-lengths apart, thus producing lobes in the aerial pattern at intervals of about 3°. Each aerial consists of an array of six full-wave dipoles giving a vertically directed beam of width ± 22° and ± 9° in the north–south and east–west directions respectively. The recording apparatus is a simplified form of the type described by Machin, Ryle and Vonberg¹, whereby the receiver is continually switched to a standard noise diode source which is automatically adjusted by a servo-mechanism to equalize the received radiation.