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.
As of June 2006, this page will begin evolving into a
more complete "zoo" of the various detector artifacts
and anomalies that ACS users might see in their data.
You are encouraged to submit items to be included here:
if you have a prime example of one of the following
items, please identify the dataset (archival rootname),
or send a small GIF image, to mutchler@stsci.edu.
We will include a description of the anomaly: it's
source, how to mitigate against it, and how to deal
with it, if possible. In striving for completeness,
some of these well-known items may seem obvious,
but they will be sorted generally from the well-known
and obvious items, down to the more rare and exotic
variety.
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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