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Paper: ACS/HRC Astrometry for Polarizer Filters: To Fit or To Map?
Volume: 338, Astrometry in the Age of the Next Generation of Large Telescopes
Page: 126
Authors: Kozhurina-Platais, V.; Biretta, J.
Abstract: The Hubble Space Telecope's ACS/HRC camera is optimized for high resolution (27 mas/pix), allowing us to reach a sub-mas regime in differential astrometry. Here we consider the ACS/HRC astrometric properties through polarizer filters, if one would like to compare polarized and non-polarized images of the same targets. The geometric distortion of polarizer filters not only has the low- and high-frequency components, as found by Anderson & King for wide-band filters, but also shows a complicated anisotropic structure tightly correlated with polarization angle. Thus, instead of a polynomial model, the mapping technique was used in differential mode to correct for distortion, which at maximum reaches 15 mas. As a result, the post-correction residuals show only 0.8 mas scatter. At the moment, the ACS/HRC is the only existing imaging instrument capable of delivering sub-mas astrometry in various filters from a single observation, although in a very small field-of-view.

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