Astrometric Correction for WFC3/UVIS Lithographic-Mask Pattern
Abstract
Observations of the central field in Cen taken with large dither patterns and over a large range of HST roll-angles exposed through F606W UVIS filter hav e been used to examine the lithographic-mask pattern imprinted on the WFC3/UVIS detec tor during the manufacturing process. This detector defect introduces fine-scale astrome tric errors at the level of about 0.2 pixel with a complicated spatial structure across the WFC3/ UVIS CCD chips. The fine-scale solution was utilized to construct a 2-D look-up table for co rrection of the WFC3/UVIS lithographic-mask pattern. The astrometric errors due to th is detector defect have been cor- rected down to the ~ 0.05 pixel level. The derived 2-D look-up table can be interpol ated at any point in the WFC3/UVIS image by ST software DrizzlePac / AstroDrizzle. The main results of these calibrations are: 1) new polynomial coefficien ts of geometric distortion for 14 calibrated UVIS filters in the form of Instrument Distortion Co rrection Table (IDCTAB file) were improved to account for the lithographic-mask pattern i n the WFC3/UVIS detector; 2) new derived look-up table in the form of a D2IMFILE, which sig nificantly improves (30-60%) the fine-scale structure in the WFC3/UVIS geometric distorti on; 3) geometric distortion cou- pled with the D2IMFILE and new improved IDCTAB can now be succ essfully corrected to the precision level of ~ 0.05 pixel (2 mas) for the UVIS detector.
- Publication:
-
Space Telescope WFC Instrument Science Report
- Pub Date:
- July 2013
- Bibcode:
- 2013wfc..rept...14K
- Keywords:
-
- Hubble Space Telescope;
- Space Telescope Science Institute;
- STScI;
- HST