Towards Imaging of Star Clusters by Speckle Interferometry

Abstract

Labeyrie’s (1970, 1976) speckle interferometry permits an astronomical object to be resolved to a limit approaching λ/D (where λ is the mid-band wavelength of the light accepted by a telescope having a pupil aperture of diameter D) in the presence of severe atmospheric seeing. As Dainty (1973) has pointed out, this resolution limit is virtually independent of the accuracy to which the telescope is figured — the seeing can actually improve a telescope’s resolution! Even though a true image of the object cannot usually be constructed by Labeyrie’s data reduction procedures, nevertheless the autocorrelation of (the distribution of brightness over) the object can always be reconstructed — provided the extent (width, apparent angular diameter) of the object does not exceed that of the isoplanatic patch (cf. Bates and Gough, 1975). The autocorrelation is useful because its extent is necessarily twice that of the object.