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Paper: On the Fly Bad Pixel Detection for the Chandra X-ray Observatory's Aspect Camera
Volume: 238, Astronomical Data Analysis Software and Systems X
Page: 439
Authors: Cresitello-Dittmar, M.; Aldcroft, T. L.; Morris, D.
Abstract: The Chandra X-ray Observatory uses an optical CCD in its aspect camera. As with all space-based CCD detectors, radiation damage will accrue with time and substantially increase the dark current of individual pixels, resulting in ``warm pixels.'' In order to obtain the most accurate aspect solution possible, it is necessary to identify and compensate for these regions when processing the guide star images. If a warm pixel is included in a guide star image, it will bias the centroid location for that image. As the spacecraft dithers, this bias will introduce a wobble to the star location that translates to a wobble in the aspect solution. Special dark current calibration observations can be taken to provide a full-frame dark current map, however, it is not operationally feasible to obtain a new map for each observation. The CXC data systems group has developed software to analyze the star image data and identify warm pixels as part of standard processing. This ``on the fly'' determination allows us to adjust for variations in CCD conditions between dark current calibration observations and provides useful information for identifying bad regions on the Aspect camera CCD.
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