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Hubble Space Telescope
Incorrect COS ACQ/IMAGE coordinate keywords

The WCS (World Coordinate System) keywords for COS ACQ/IMAGE observations contain an error in the reference pixel for the WCS coordinates. The header keywords "CRPIX1" and "CRPIX2" are set to the center of the detector (512,512), when they should be set to the center of the aperture (which can be different for each observation).

Users drafting and submitting Phase II HST programs should remember that the coordinates given by the COS WCS are only as accurate as the coordinates of the guide stars used, and may contain additional sources of pointing error. These coordinates therefore do not pass the 0.4" requirement to skip ACQ/SEARCHs during COS Target Acquisitions.