Issues with CCDs that may have affected the quality of DECam observations are recorded on the DECam CCDs page.
Headers may be inconsistent with catalog values for about 2% of bricks in the Tractor catalogs. This is due to some files being altered while rsync processes were running.
A very small number of
ref_id values for Gaia sources appear twice in the Tractor catalogs. One of the duplicates corresponds to the
"correct" Gaia source and the second duplicate has all of the correct information for a Gaia source but with an incorrect
ref_id that would be correct for the second duplicate is missing entirely from the Tractor catalogs.
An example from DR9 is
ref_id 303293444934132224, which appears in Tractor catalog
correct information (RA, Dec, etc.) and in Tractor catalog
tractor-0238p305.fits with information that actually
corresponds to the Gaia source with
The cause of this problem has yet to be fully diagnosed, although the discrepant Gaia sources tend to lie very close to the boundaries of a brick.
This issue will also propagate to the sweep files.
A few dozen bricks were intractable on a reasonable timescale as they overlapped regions of high source density. These
bricks were "bailed out" of before they finished processing. Sources in such bricks can be identified as they have
BAILOUT flag set in the MASKBITS bitmask.
In addition, certain high-density regions are missing completely from the Legacy Surveys. A good example is the Large Magellanic Cloud.