THE DETERMINATION OF STELLAR MAGNITUDES BY ELECTRONOGRAPHY

Abstract

The application of electronography to stellar photometry is investigated, and it is shown that a linear relationship between the area under the density profile of the star image and the intensity of the star exists over a range of at least 4.6, and probably in excess of 5, magnitudes beginning at the plate limit. The advantages of this method of photometry are discussed. Linear Response One of the major advantages of the electronographic-type image converter ( or electronic camera ) is the linear relationship between the intensity of light incident upon the photocathode and the specular density of the electronographic plate. The problem of the response of photographic emulsions to electrons has been extensively investigated both theoretically and practically by workers in the field of electron microscopy. These investigations are summarized by Valentine (1966), who also gives references to earlier work. These studies have shown that when a photographic emulsion is exposed to electrons of the energies used in electronographic-type image converters, each electron is sure to render developable one or more of the silver halide crystals through which it passes. On the other hand, the cooperative action of several photons on a given halide crystal is required to render it developable. These two processes are referred to as single-hit and multiple-hit processes. Valentine has shown that the specular photographic density D, which is defined by * Contributions from the Lick Observatory, No. 248.