THE GREAT-CIRCLE CAMERA - A NEW DRIFT-SCANNING INSTRUMENT

We discuss the design, construction, and use of a new class of scannin g camera that eliminates a critical limitation of standard CCD drift-s can observations. A standard scan, which involves no correction for th e differential drift rates and curved stellar paths across the field o f view, suffers from severe image degradation even when one observes a t moderate declinations. Not only does this effect limit the area of t he sky over which drift scanning is viable but, as detector sizes incr ease, CCD mosaics become standard, and dome/telescope seeing improves, the area of sky for which scanning is acceptable (image degradation l ess than or similar to seeing) will be further reduced unless some act ion is taken. By modifying the scan path (the path on the sky traced b y signal accumulated along a single CCD column) to lie along a great c ircle on the sky rather than along a path of constant declination, ima ge degradation is minimized. In this paper, we discuss the design and implementation of a stage that rotates and translates the CCD during a drift-scan exposure so that the scan path is along a great circle on the sky. Data obtained during the commissioning run of the Great Circl e Camera at the Las Campanas 1-m telescope are presented.