Interferometry of the intensity fluctuations in light III. Applications to astronomy

Abstract
A theoretical analysis is given of the application of an intensity interferometer to the measurement of the angular diameters of stars and the performance of such an instrument is calculated for representative parameters of the apparatus. It is shown that observations with an intensity interferometer are probably limited by the inherently low sensitivity of the technique to the stars visible to the naked eye, but that the resolving power, which is determined by the limitations of radio rather than of optical technique, should be great enough to measure any star, however hot, of sufficient apparent brightness; furthermore, the operation should be substantially unaffected by atmospheric scintillation. Very cool stars of adequate apparent brightness would be completely resolved by the individual mirrors of an intensity interferometer and this fact limits the technique to stars of spectral type earlier than about K5. However, a modified form of interferometer using a single main mirror should enable this limit to be extended to bright stars of spectral type as late as M5. Some applications of an intensity interferometer to measurements of both single and double stars are discussed briefly and it is concluded that such an instrument might be of value in astronomy.

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