Astrometry and photometry with HST WFC3. II. Improved   geometric-distortion corrections for 10 filters of the UVIS channel
  We present an improved geometric-distortion solution for the Hubble Space Telescope UVIS channel of Wide Field Camera 3 for ten broad-band filters. The solution is made up of three parts: (1) a 3rd-order polynomial to deal with the general optical distortion, (2) a table of residuals that accounts for both chip-related anomalies and fine-structure introduced by the filter, and (3) a linear transformation to put the two chips into a convenient master frame. The final correction is better than 0.008 pixel (~0.3 mas) in each coordinate. We provide the solution in two different forms: a FORTRAN subroutine and a set of fits files, one for each filter/chip/coordinate. 
A. Bellini (1), J. Anderson (2), L. R. Bedin (2), ((1) Univ.PD, (2)   STScI)
astro-ph.IM