Speckle interferometry observations at Mount Palomar

Speckle Interferometry has originated as an extension of methods previously used by Fizeau, Michelson and Pease for observing stellar details in the presence of atmospheric seeing. The « fine structure » of stellar images long reported by some observers of double stars is in fact a speckle pattern similar to that observable in diffused laser beams. As could be predicted from this interpretation, 1 000 speckles were found in the image given by the 5-meter Palomar telescope when observing in monochromatic light with short exposures. The fringes observed by Michelson and Pease, using a Fizeau screen on the aperture, are a special case of speckle which can be analyzed visually because of its simpler structure. The convolution of the specklesby details of the stellar object may be detected by time-averaging the autocorrelation function (or the power spectrum) of the instantaneous image, giving the autocorrelation function (or the power spectrum) of the object. Observations were carried out using a television sensor and optical processing techniques. The diameters of several supergiant stars were measured and limb darkening evidenced in α Orionis and o Ceti. A dozen stars were found to be binary, including Algol for which the predicted third body is thus evidenced. Future developments include observations at very low levels in the photon counting mode, and real time electronic processing. Use of several large telescopes in the synthetic aperture mode is also becoming feasible.