Diffraction-Limited Imaging with Ground-Based Optical Telescopes

The construction of diffraction-limited images with ground-based optical telescopes by means of closure-phase observations is explored. The effect of redundant baselines on closure-phase observations is analyzed, and it is shown that for bright objects a nonredundant-mask approach is superior to the use of the full aperture. Observations of closure phase with a nonredundant mask on the 200 in. Hale Telescope are presented, and compared with the predictions of atmospheric seeing theory. It is demonstrated that fairly complex images can be constructed from closure-phase observations alone.