Speckle Interferometry

The speckle interferometry technique involves processing the image before the seeing disk becomes the dominant feature of the image. This is usually done by taking short exposures (typically 15 milliseconds or less) of the star and analysing the pre-seeing-disk structure for information. Under high magnification, the area around the star reveals itself to be many "specks" (or "speckles") moving at random within a relatively confined area. Figure 17.1 shows a speckle pattern from a 4-m telescope.

Looking at many of these short exposure images in succession, one sees a sort of "shimmering" effect. This is due to interference between the individual speckles, hence the term, "speckle interferometry".

Labeyrie2 laid much of the groundwork for using speckle interferometry in a scientific capacity. Although it has been known since the time of Fizeau and Michelson (late nineteenth, early twentieth century) that resolution information lost due to the atmosphere can be regained through the use of inter-ferometric techniques, it has only been available on the brightest of objects.

Figure 17.1. A single speckle frame of the star K UMa on the KPNO 4-m. Adapted from McAlister et. al.1 Printed by kind permission of the American Astronomical Society

Figure 17.1. A single speckle frame of the star K UMa on the KPNO 4-m. Adapted from McAlister et. al.1 Printed by kind permission of the American Astronomical Society

Several groups dabbled in binary star speckle interferometry throughout the mid-1970s, but with the commonplace usage of image intensifiers in observational astronomy by the late 1970s, the true potential of speckle interferometry in binary star science was revealed to the astronomical community.3

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