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Speckle interferometry

المؤلف:  James Binney and Michael Merrifield

المصدر:  GALACTIC ASTRONOMY

الجزء والصفحة:  p-83

2026-09-08

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In 1970 A. Labeyrie pointed out that, at any instant, the pattern of light produced by a star at the focus of a large telescope is speckled. Each speckle is an independent, diffraction-limited stellar image. Turbulence in the air above the telescope causes these images to dance around by introducing fluctuations in the phase of the wave front entering the telescope. In an exposure lasting longer than a fraction of a second, all these speckles are superimposed to produce a single splodge of brightness. One says that the image has been degraded by the phenomenon of 'seeing', and refers to the splodge's full width at half maximum as the seeing.

The technique of speckle interferometry involves making a very large number of short exposures of the field. An individual exposure is so short that the speckle pattern does not move appreciably as it is taken, and thus contains information on the angular size of the star. On the other hand, even when the imaged star is fairly bright, the number of photons in an individual exposure is not great, and therefore the quality of the image it provides is poor. However, by combining information from a large number of exposures, it is possible to compensate for their poor individual quality. With a 5m telescope imaging at optical wavelengths, this method yields reliable angular diameters down to about 20 mas. A review of this method and its accomplishments is given in Labeyrie (1978).