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V. Kozhurina-Platais (STScI), J. Anderson (Rice), A. Koekemoer (STScI)
The goal of astrometric calibration of HST WFPC2 is to obtain a coordinate system free of distortion down to the precision level of 1 mas. So far such calibration has been done only for a wide bandpass F555W filter. The inner calibration field of \omega Cen exposed through filters F300W, F555W and F814W has been used to examine the geometric distortion of WFPC2 as a function of wavelength. The improved distortion correction technique by Anderson and King has been applied to obtain working sets of x,y coordinates for assorted HST WFPC2 frames with the globular cluster \omega Cen in these three bandpasses. We used a bicubic polynomial model to derive geometric distortions in F300W and F814W filters relative to the distortion-free coordinates in F555W filter. Four separate distortion corrections, each for the four WFPC2 chips have been optimized independently. The main conclusion of this study is that the differences in distortion between the filters F555W and F814W are about 1 per cent and between f555 and F300 twice as much.
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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.