Abstract
High quantum-efficiency, excellent linearity, and low noise make frame-transfer silicon Charge-Coupled Devices (CCDs) ideal imagers at very low light levels in the UV to 900 nm range. Scientific-grade CCDs are now available with less than 10e noise from at least four manufacturers. In astronomy these CCDs on large and small telescopes enable studies of objects 100 times fainter than is possible using photographic and video-camera techniques. This is due both to the high quantum efficiency and the photometric stability of the CCD. Chopping techniques, taking advantage of this stability, allow cancellation of low-level systematics. Detection levels of 2×10-5 photons m-2 nm-1 sec-1 pixel-1 have been achieved. Faint galaxies and stars of 30th magnitude are detected in 6 hours integration on a 4 meter telescope, corresponding to 0.02 photons/sec/pixel. Soon the efficiency of large telescopes for survey studies will be improved by the use of CCD mosaics, covering the entire usable focal plane.
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