The COS/STIS team at STScI has created a stand-alone automated script to apply Charge Transfer Inefficiency (CTI) corrections to STIS CCD data. The script will remove trails and other artifacts caused by CTI effects in the CCD detector, and will help correct target fluxes and positions to their proper values. The script uses a pixel-based correction algorithm based on the work of Anderson and Bedin (2010) and runs in Python.
The script should be fairly easy to use. Once the raw science images are on disk and the script installed, only a simple one-line command is needed to start the processing. The script will then take-over and automatically process that data. The script will automatically generate CTI corrected dark reference files, apply CTI corrections to the science data, and output the usual CALSTIS products with CTI corrections applied. If the script cannot find all the dark images it needs, it will provide a web link where the required dark images can be downloaded.
Version 1.0 of the script was released in the September 2015 STAN. Currently only the most common observation modes are supported -- full-frame, non-binned data, taken with the default CCD amplifier. Future enhancements may include sub-array data.
The script and further information can be found at these links:
See the following Instrument Science Reports (ISRs) and references therein for comparisons of the old empricial CTI corrections and the new pixel-based CTI correction:
- STIS ISR 2022-03 (Prichard, 2022): Comparison of STIS CCD CTI Corrections on Photometry
- STIS ISR 2015-05 (Biretta et al., 2015c): Astrometric Performance of STIS CCD CTI Corrections on Omega Cen Images
- STIS ISR 2015-04 (Biretta et al., 2015b): Photometric Performance of STIS CCD CTI Corrections on Omega Cen Images
- STIS ISR 2015-03 (Biretta et al., 2015a): STIS CCD CTI Column and Temperature Dependence
The image below shows a comparison of the current HST archive products (June 2015), and results using the new CTI correction script (version 1.0). The image is of the Omega Cen cluster, and is a region near the bottom of the CCD detector (far from the amplifier) where CTI effects are large. The archive image shows significant trailing on stars and hot pixels, which is greatly reduced in the corrected image. The script can also correct spectra, and will similarly reduce trailing and artifacts in spectra.