IRAS Explanatory Supplement
XI. Known Processing Anomalies
A. Processing of Extended ("Cirrus") Sources as Point
Sources
Chapter Contents
| Authors
| References
Table of Contents |
Index | Previous Section
| Next Section
As discussed in
Section V.C, the point source recognizer
can be triggered by sources that are of unlimited extent in the
cross-scan direction long as they are less than about 1' in the
in-scan direction. While this characteristic was recognized early
in the design of the software, it was felt that this situation
would arise much less frequently than the case where several true
point sources triggered many cross-scan detectors simultaneously.
The presence of "infrared cirrus" and the extended
sources in the Galactic plane means that at 100 µm in particular
the sky is dominated by extended structures rather than by clusters
of point sources. The detection and confirmation software thus
created strings of pseudo-point sources spread along the cross-scan
direction.
In retrospect, it would have been better to adopt a different
approach. for example, whenever four or more cross-scan detectors
were triggered, all such detections should have been discarded
from the point source catalog or placed in a special data base
to compare different scans to verify that these detections were
in fact due to several true point sources. The consequences of
the present approach are clear. At 100 µm the point source catalog
is unavoidably contaminated by the presence of point-like condensations
within the extended emission and by the effects of cirrus on discrete
point sources that include missing fluxes at shorter wavelengths
caused by band-merging diffculties.
Chapter Contents
| Authors
| References
Table of Contents |
Index | Previous Section
| Next Section