IRAS Explanatory Supplement
XI. Known Processing Anomalies
K. Minor Problems
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- An unmodelled source of position errors was present in the data, as evidenced by the need to increase in-scan (X) for sources that had a cross-scan position error without a significant uniform component.
- Radiation hits and noise spikes caused some sources to have significantly larger cross-scan errors than quoted.
- In order to improve completeness, it was necessary to allow detection without a confirming partner due to a failed detector to bypass seconds-confirmation. This resulted in a large number of spurious detections being accorded a status equal to that of a truly seconds-confirming source. These false detections could at times replace valid detections in band-merging.
- A second effect of failed detections was that an edge detection pair opposite a fulled detector was often not seconds-confirming allowing two separate detections to be present at band-merging. The weaker detection, with its larger error basis, was usually chosen in band-merging resulting in a depressed flux in that band.
- A third effect of failed detectors resulted from detectors that were impaired but not dead. They would produce detections that were too weak to seconds-confirming with detections on the partner detectors. Again, the weaker detection would often be chosen in band-merging resulting in a depressed flux.
- Strong radiation hits could also result in a seconds-confirming failure which, in a small fration of cases caused incorrect fluxes or flux status.
- Responsivity changes due to particle or photon radiation caused baseline changes of order 10% in some observations.
- The optimum thresholds for accepting the seconds-confirmed sources were set by varying the threshold level and evaluating the numbers of sources passed as a function of threshold value (Section VII.E.5). The method worked satisfactorily in all the wavelength bands but the 25 µm band where the total number never reached the predicted plateau.
- The CIRR2 flag is incorrectly set to 0, implying no all sky data, for about 40 sources at the 0 = 360' ecliptic longitude boundary.
- For many catalogs, the truncation instead of rounding of optical magnitudes leads to a 0.1 mag error in the reported magnitudes.
- For the ESO/Uppsala Survey of the ESO (B) Atlas, only the first two characters of the catalog description were used for the type field.
- Objects near the ecliptic poles which were scanned twelve times within six successive SOPs produced three separate HCONs. The first and last HCONs were allowed to weeks-confirm normally, while the second HCON was only combined with the source by the clean-up processor. Due to a software design error this program created a small number of sources having two HCONs with identical fluxes.
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