Optical and Radio Occultation Analysis

Abstract

The study of occultations of radio sources by the Moon has proved a powerful method of studying the structure of radio sources with a resolution limit, in some cases, as small as 0″.1 and at the same time of obtaining positions of the radio components with an accuracy of the order of 0″.1 to 1″. Recent optical observations of occultations suggest that the method is likely to play an important role in the measurement of stellar diameters down to about 0″.001 and in the detection and measurement of binary star systems. Over the past several years considerable experience has been gained in the analysis of the occultation curves of radio sources and, since the problems encountered are common to both the optical and radio analysis, our conclusions on how best to analyse occultation curves may be of some interest to the optical workers and also to radio observers who have recently entered the field. Before discussing the methods of analysis and also before discussing some essential differences between the optical and radio work it is useful to consider in some detail the nature of the occultation curve of a simple source of small angular size. It is not proposed here to give a detailed account of the methods of analysis but to indicate the general principles along which the analysis should proceed so as to enable the choice of the most appropriate method in a particular case. A simple treatment of Scheuer’s convolution procedure is given and a simple derivation of the resolution limit imposed by the receiver bandwidth.