Diffraction-limited imaging. III - 30 MAS closure phase imaging of six binary stars with the Hale 5 M telescope

Images of six binary stars that show diffraction-limited resolution for the Hale 5 m telescope are presented. This corresponds to a resolution of about 30 mas at 630 nm. The images were constructed from analysis of photon-limited speckle interferograms, with between about 200 and 1100 recorded photons per atmospheric coherence time. Using a new application of the CLE, the diffraction-limited Fourier amplitudes of the objects were first recovered. The recovery of the object Fourier phase was accomplished through bispectral analysis of the specklegrams. This analysis yields the object closure phases, from which the Fourier phases are then extracted by a least-squares minimization. Direct Fourier inversion then produces the final images reported here. The dynamic range of the resulting images varies from 3:1 to about 20:1. The seeing for the majority of observations was estimated to be about 1.2 arcsec on average. Thus, for these simple objects, such imaging techniques are capable of achieving a factor of 40 improvement in resolution while retaining a contrast of 2-3 mag, under photon-noise-limited conditions.