WFC3 - Geometry Distortion and Multidrizzle
Abstract
During HST Servicing Mission 4 in May 2009, Wide Field Camera 3 (WFC3) replaced WFPC2. WFC3 is comprised of two channels, the UVIS channel, which contains two 2Kx4K- pixel CCD detectors, and an IR channel, which contains a 1Kx1K-pixel detector. During the WFC3 Servicing Mission Observatory Verification program we performed a preliminary calibration of WFC3's image distortion. Images of astronomical extended objects on the UVIS and IR detectors have 7% linear distortion,principally caused by the inclination of the camera focal planes to the telescope's principal rays. We determined the coordinate transformations between the sky and the WFC3 focal plane, which include distortion, rotation and translation. The transformation for each UVIS CCD is treated separately, whereas the monolithic IR detector requires only a single transformation. We acquired observations of astrometric fields in 47 Tuc and the LMC consisting of 30 UVIS F606W pointings and 24 IR F160W pointings. We find that a fourth order polynomial fits the optical distortion with residuals of 0.05 pixel (2 milliarcseconds) in the UVIS channel and 0.06 pixel (8 milliarcseconds) in the IR channel. Although these residuals contain systematic variations indicative of higher order polynomial terms and possibly filter-dependent, high-frequency distortion, the results reported here can be used to combine images, e.g. using STScI's MultiDrizzle application.
- Publication:
-
American Astronomical Society Meeting Abstracts #215
- Pub Date:
- January 2010
- Bibcode:
- 2010AAS...21546309K