A MEASUREMENT OF ISOPLANATISM WITH THE HIGH-RESOLUTION CAMERA AT THE CANADA-FRANCE-HAWAII TELESCOPE

A long-exposure CCD frame has been obtained with image quality of 0".26-0".34 (FWHM) using the DAO/CFHT image-stabilizing camera at the prime focus of the Canada-France-Hawaii Telescope. The entrance aperture was stopped down to 1.2 m and, at this aperture size, the effect of imperfect isoplanatism is seen by comparing images of stars of varying distances from the guide star. The deterioration of the image quality is seen to occur faster along the direction toward the guide star, thus elongating the images, as expected from theoretical considerations. A centrally peaked "Bismark" profile is found to best fit the shape of the stabilized point-spread function. It is pointed out that new image-analysis tools will be required to fully exploit astronomical data obtained with adaptive optics systems.