Large-area CCD mosaic for astronomical imaging

Large area charge-coupled devices (CCDs) with unprecedentedly low noise and high quantum efficiency are revolutionizing astronomy probing the universe to record faint levels while imaging relatively large areas of the sky. On-line intelligent pattern recognition software transforms these large images into photometrically accurate catalogs of colors sizes and shapes of thousands of stars and galaxies. The scientific driver for this is starvation: much of modern optical and JR astronomy is " photon starved" . Current research involving faint imaging and spectroscopy often requires total exposure times longer than several nights to obtain good signal-to-noise ratio. One must use the highest quantum efficiency detectors on the largest telescopes and develop image acquisition and reduction techniques which cancel systematic errors to high accuracy. We describe here a CCD mosaic camera and data handling system which will make full use of the light collected by the largest existing telescopes. It uses off-the-shelf CCDs in a mosaic configuration together with automated data acquisition and processing. 2. ULTRA-FAINTCCI) IMAGING IN ASTRONOMY In practice an arbitrary precision in photometry cannot be reached even in an arbitrarily long integration time. Accurate surface photometry to 30-3 1 magnitude arcsecond2 requires the correction of systematic errors to iO-4 of the moonless night sky background. New techniques for ultra-deep imaging made possible by the dimensional and temporal stability of CCDs permit photometry at this level. A series of guided exposures each