ACS/WFC Revised Geometric Distortion for DrizzlePac
Abstract
The goal of the ACS/WFC astrometric calibration for DrizzlePac is to provide a coordinate system free of distortion to a precision level of ∼0.1 pixels (∼ 5mas). The astrometric calibration of ACS/WFC is based on the astrometric standard field in the vicinity of globular cluster 47 Tuc. We used a polynomial model to derive the geometric distortion in the WFC channel relative to the distortion-free coordinates, which now accounts for proper motions of stars in the astrometric field. A new and straightforward representation of time-dependent distortion in the linear terms is now implemented in the IDCTAB reference file and in the STScI software DrizzlePac to obtain simultaneously the ACS/WFC geometric distortion and its time-dependent correction. As a result, the geometric distortion can be corrected down to a precision level of 0.02 pix (1mas), which allows now for improvement of the alignment and registration of the ACS/WFC images with accuracy of ∼0.05 pix (2.5mas) or better.
- Publication:
-
Instrument Science Report ACS/WFC 2015-06
- Pub Date:
- June 2015
- Bibcode:
- 2015acs..rept....6K
- Keywords:
-
- Hubble Space Telescope;
- Space Telescope Science Institute;
- STScI;
- HST