Infrared Astronomical Satellite, IRAS

The Small-Scale Structure (SSS) Catalog, also known as the catalog of "small extended sources," contains sources resolved by the IRAS in any band (12, 25, 60, or 100 microns) but smaller than 8' in angular extent. These non-pointlike sources are nevertheless discrete, and this catalog complements the Point Source Catalog, and the atlases of extended emission, e.g., the ISSA plates. The SSS Catalog gives the infrared characteristics of 16,740 objects including galaxies, planetary nebulae, and compact H II regions.
Sources are defined by excursions in sky brightness detectable above the local baseline on spatial scales smaller than 8', excluding point sources. The catalog lists several quantities for each entry and in each band separately: a position accurate to about 1' (rms); a flux density accurate to 50% (rms) overall, and better at high signal-to-noise ratios; a rough indicative size if a point source is present at the same location; and a variety of warning and processing flags.

Incompleteness is a complex function of wavelength band, brightness, and location, so the absence of an entry in the SSS Catalog does not necessarily imply the lack of detectable extended emission. Many entries, mostly at 60 and 100 microns, refer only to emission features that are details in larger structures known as Galactic cirrus. Complete documentation is contained in the printed version (see reference).

While small-scale structure cannot be defined or measured with the same finality as point sources, Catalog entries always represent correlated and confirmed events in the detector output, making them valuable pointers to the IRAS images and raw data. The SSS processor has distilled from the survey a wide variety of objects and provided reasonable estimates of their parameters, but if a detailed shape description, or more accurate position, flux, or size are needed, it is necessary to go back to the fundamental reference, the raw detector output.

Reference:
IRAS Catalogs: The Small Scale Structure Catalog, 1988, ed. G. Helou and D.W. Walker, NASA RP-1190, vol 7 (Washington, DC: GPO).

Version and release date: 1.0, 1985 Dec

Small-Scale Structure Catalog

See the format of the Catalog

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