The First Diffraction-Limited Images from the W. M. Keck Telescope

The first diffraction limited, 0.05" resolution, images on the W. M. Keck Telescope have been obtained at a wavlength of 2.2 microns. These images were part of an experiment to test the suitability of the Keck Telescope for speckle imaging. In order to conduct this test, it was necessary to modify the pixel scale of the Keck facility Near Infrared Camera (NIRC) to optimally sample the spatial frequencies made available by the Keck Telescope. The design and implementation of the external reimaging optics, which convert the standard f/25 beam from the secondary mirror to f/182 are described here. Techniques for reducing speckle data with field rotation on an alt-az telescope are also described. Three binary stars were observed in this experiment with separations as small as 0.05". With only 100 frames of data on each, a dynamic range of at least 3.5 mag was achieved in all cases. These observations imply that a companion as faint as 14.5 mag at 2.2 microns could be detected around an 11th magnitude point source.