QUOTA - An Advanced Mosaic Imager
Abstract
QUOTA is an 8Kx8K (16'x16') optical imager that uses four 4Kx4K orthogonal transfer CCDs arrays (OTAs). Each OTA has 64 nearly independent CCDs having 480x494 12µm pixels. By reading out several of the CCDs rapidly (20 Hz), the centroids of the stars in those CCDs can be used to measure image motion due to atmospheric effects, telescope shake, and guide errors. Motions are fed back to the remaining 250 CCDs that continue to integrate normally, allowing a shift of the collecting charge packets so that they always fall under the moving star images, thereby effecting low order AO tip/tilt correction in the silicon to improve image quality. As a bonus, the stars that are read rapidly can be studied for high speed variability.
Although QUOTA was intended as a pioneering prototype for WIYN's 32Kx32K One Degree Imager (ODI), providing a means to test the technical developments needed for ODI (e.g., detectors, controllers, optics, software), it is a useful mosaic camera on its own. With WIYN's r-band median seeing of 0.7", we have already seen that orthogonal transfer guiding improves the images by about 0.15", to about 0.55". The gains are most effective over the isokinetic patch, 2' from a guide star. QUOTA's design allows for up to 32 guide stars across the field of view to provide for excellent correction when the target field is rich in bright stars (V<14). In its current configuration, QUOTA will have been to the telescope twice prior to the AAS Meeting. We will report on the performance of this imager: the degree of image quality improvement with readout speed and wavelength, the field over which the correction is effective, and the accuracy of the high speed photometry. QUOTA was funded in part by NSF/ATI grant AST-0352979.- Publication:
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American Astronomical Society Meeting Abstracts #213
- Pub Date:
- January 2009
- Bibcode:
- 2009AAS...21347406J