ACS anomalies and artifacts
Figure: This WFC frame exhibits bias offsets between amplifier quadrants,
correlated noise imposed by the distortion correction
(Moire-like pattern), and glint (scattered light centered
on the interchip gap). Click to enlarge image.
Listed below are various detector artifacts
and anomalies that ACS users might see in their data.
See also the more detailed HLA report,
ACS CCD Image Anomalies in the Hubble Legacy Archive (PDF).
General HST observing anomalies
- Guide star issues: loss of lock, no guide stars
- Cosmic rays: normal, SAA, cascading, residual
- Satellite trails
- Asteroid trails in fixed target images
- Star trails in moving target images
ACS optical features and artifacts
ACS detector features
- WFC interchip gap
- HRC occulting finger
ACS detector artifacts
- Hot and warm pixels: corrected, uncorrected
- Bad CCD columns, and saturated blobs in darks
- CCD amplifier crosstalk (electronic ghosts)
- Dragon's Breath scattered light from an off-chip star
- Glint from a star in the WFC gap
- Bleeding along CCD columns from saturated objects
- Bias offset between WFC amplifier quadrants
- CTE tails
- Optical ghosts from filter reflections, generated by bright stars
- HRC prism issues: red leak / pile-up for blue filters
Artifacts generated by image processing and combination
- Correlated noise (crosshatch pattern in sky background)
- Image compression data loss or artifacts
- Residual (unrejected) cosmic rays and artifacts
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