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IRAS_FSC: IRAS Faint Source Survey


Table name: 	IRAS_FSC
Records:  	173044
Version:	Version 2.0
Spectral Band: 	IRband
Kind of Object: IRASLog
Mode: 		Survey
Coordinates: 	J2000



The Infrared Astronomical Satellite (IRAS) conducted a survey of 98% of the sky from January to November, 1983 in four wavelength bands centered at 12, 25, 60, and 100 microns. It spent approximately two-thirds of the 300-day mission performing an unbiased survey of the sky, leading to the release in 1984 of the IRAS Point Source Catalog (PSC) containing some 250,000 sources.

The PSC along with other aspects of the IRAS mission are explained in detail in the Explanatory Supplement to IRAS Catalogs and Atlases (1988).

The IRAS survey was designed to produce an extremely reliable catalog. The sky was scanned repeatedly by multiple detectors, and over half of the sky was covered by more than 12 individual detector scans per band. The PSC was produced by detecting sources in each of the individual detector scans, and then applying a series of stringent confirmation criteria to establish the reliability of those sources. This led to a reliability of the PSC which exceeded 99.997% over most of the sky, excluding cirrus sources, but at the cost of not reaching the full sensitivity attainable with the IRAS data.

The IRAS Faint Source Survey (FSS) has achieved roughly a one magnitude increase in sensitivity (a factor of approximately 2.5) relative to the PSC by coadding the data before extracting sources.

The FSS was produced by point-source filtering the individual detector data streams, and then coadding those data streams using a trimmed-average algorithm. Thus, confirmation is still applied to the data but in a much less stringent manner than was applied for the PSC. Three major data products were produced: images, a catalog, and its associated reject file.

The Faint Source Catalog (FSC) is a compilation of the sources extracted from the FSS plates that have met reasonable reliability requirements. For the faintest sources in the FSC, the reliability must exceed roughly 99% at 12 and 25 microns and 80% at 60 and 100 microns. The "false" 20% at 60 and 100 microns result primarily from the infrared cirrus. The catalog as a whole is at least 99% reliable at 12 and 25 microns, and approximately 93% at 60 and 100 microns (see Section III.D in the Faint Source Survey Supplement for further information). Although the reliability of the FSC cannot be as high as that of the PSC, which was > 99:997% at 12, 25 and 60 microns, and approximately 93% at 100 microns (due also to cirrus) overall, the FSC is still a highly reliable catalog, and can be used by astronomers with virtually the same degree of confidence with which the PSC has been used.

A copy of the documentation should accompany any computer-readable version of the catalog. The FITS Table header(s) in this file only give the basic format of the catalog. Please refer to the documentation or source reference for a more detailed discussion of the data.


Name		Meaning

name		Source Name (IRAS designation) 
ra_ori		1950 Right Ascension
dec_ori		1950 Declination
major		major semi-axis of the uncertainty ellipse (") 
minor		minor semi-axis of the uncertainty ellipse (")
posan		position of major ellipse axis (from North, degrees)
nid		number of positional associations
idtype		type of object association: 
			1 for extragalactic, 
	            	2 for stellar
		 	3 for other
		        4 for multiple
catnb		No. of nearby catalog sources
f1		the fluxes in Janskys (= 10**-26 W/m/m/Hz) at 12 microns
f2		the fluxes in Janskys (= 10**-26 W/m/m/Hz) at 25 microns
f3		the fluxes in Janskys (= 10**-26 W/m/m/Hz) at 60 microns
f4		the fluxes in Janskys (= 10**-26 W/m/m/Hz) at 100 mic.
q_f1		qualities from 1 (high) to 3 for the first passband
q_f2		qualities from 1 (high) to 3 for the second passband
q_f3		qualities from 1 (high) to 3 for the third passband
q_f4		qualities from 1 (high) to 3 for the fourth passband
u_f1,2,3,4	uncertainty expressed in units of 100* (DEL )Flux / Flux
snr1,2,3,4	(Signal/Noise) for passband
lsnr1,2,3,4	Local Signal/Noise Ratio for passband
area1,2,3,4	No. of pixels with flux   3 * noise
nobs1,2,3,4	No. of individual detector sightings
extnr1,2,3,4	No. of extractions within a radius of 6 arcmin
noisc1,2,3,4	Noise correction factor
noisr1,2,3,4	Ratio 85% to 68% of flux distribuition
confuse		Confusion flags (see IRAS_Flags)
cirrus		No. of nearby 100 micron only extraction
ra		2000 Right Ascension
dec		2000 Declination
lii		2000 Galactic Longitude
bii		2000 Galactic Latitude

Flags in the IRAS catalogue refer to the 4 passbands, and are hexa-encode:
		12(mu_)	25(mu_)	60(mu)	100(mu_)
	1				x
	2			x
	3			x	x
	4		x
	5		x		x
	6		x	x
	7		x	x	x
	8	x
	9	x			x
	A	x		x
	B	x		x	x
	C	x	x
	D	x	x		x
	E	x	x	x
	F	x	x	x	x