A Preliminary Measurement of the Angular Diameter of α-Lyrae

Abstract

IT has been shown by Hanbury Brown and Twiss^1–3 that the correlation between the fluctuations in the outputs of two photo-electric detectors illuminated by a source of finite size depends on the angular distribution of brightness over the source. Measurement of the variation of this correlation with separation of the two detectors thus provides a method of measuring the angular diameters of bright stars. An experimental interferometer in which the photo-electric detectors were situated at the foci of two searchlight mirrors was constructed at Jodrell Bank in 1956 and successfully tested on Sirius^4,5. Following this work a large instrument was designed to measure all the stars in the Southern Hemisphere of spectral type earlier than FO which are brighter than photographic magnitude + 2.5. The new instrument differs chiefly from the pilot model⁴ in having mirrors of diameter 22 ft. moving on a circular railway track of diameter 618 ft. corresponding to a maximum resolution of the order of 0.0005 sec. This stellar intensity interferometer⁶, which will be described in detail elsewhere, is at present nearing completion at the Narrabri Observatory of the Chatterton Department of Astronomy of the School of Physics, University of Sydney.