Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21725440p&link_type=abstract
American Astronomical Society, AAS Meeting #217, #254.40; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
Images formed by the WFC3 IR and UVIS channels are distorted from a tangent plane projection of the sky by of order 10%. General fourth order polynomials adequately represent the distortion field of each channel. For WFC3, we calibrate the coefficients of the polynomials from the measured positions of stars in images of the globular cluster omega Cen and astrometric catalogs of their positions. Such polynomials obtain 0.1-pixel accuracy, which is sufficient for the MultiDrizzle PyRAF task to combine mosaics of exposures, to reject cosmic rays artifacts, and to co-add dithered images. Refractive elements (optical filters, windows, and correctors) perturb the distortion field, which may be represented by filter-dependent polynomial coefficients. We present the calibration of 10 of the UVIS-filter polynomials and 5 of the IR-filter polynomials, and the filter dependence of the variation of the distortion field. Images formed by the HST Optical Telescope Assembly suffer variations due to changes in temperature during an orbit. We present measurements of the orbital and secular variation of the image scale and skew caused by that variation. The stated accuracy of the calibrations is verified by the comparison of pairs of rectified images taken through different filters, at different pointings, and at different telescope orientations.
Cox Catherine
Dulude Michael
Kozhurina-Platais Vera
Mack Jennifer
Petro Larry D.
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