IRAS Serendipitous Survey Catalog Format

[Adapted from the Explanatory Supplement to the IRAS Serendipitous Survey Catalog]

The SSC is distributed as an ASCII file, with each source occupying three or more 80-byte records, as described in Table 1.

                  Table 1.  Format of the SSC

Start	Name		Description			Units			Format
Byte	
00	NAME		Source Name						11A1
11	HOUR		Right Ascension 1950		Hours			I2
13	MINUTE		Right Ascension 1950		Minutes			I2
15	SECOND		Right Ascension 1950		Deci-seconds		I3
18	DSIGN		Declination Sign		±  			1A1
19	DECDEG		Declination 1950		Degree			I2
21	DECMIN		Declination 1950		Arcmin			I2
23	DECSEC		Declination 1950		Arcsec			I2
25	SPARE		1 spare byte						1A1
30	FLUX		Averaged Non-color		Jansky			4E9.3
			corrected flux			(1E-26 W m-2 Hz-1)
			densities (1 value
			per band)
66	FQUAL		Flux Density Quality					4I1
			(1 value per band)
70	RGRID		Reference Grid Number					I5
76	SPARE		9 spare bytes						9A1
---- New Record ----
80	RELUNC		Percent Relative Flux					4I3
			Density Uncertainties
			(1 value per band)
92	TLSNR		10x Local Singal-to-Noise				4I4
			Ratio (1 value per band)
108	CC		Point Source Correlation				4A1
			Coefficient (1 value per
				band)
112	TRFLUX		10 x F(c)/F(r)						4I2
120	POSDRS12	Right Ascension Delta		±  			1A1
			Sign
121	POSDR12		Right Asension Delta		Arcsec			I3
124	POSDDS12	Declination Delta Sign		±  			1A1
125	POSDD12		Declination Delta		Arcsec			I3
128	Repeat for 25 micron band
136	Repeat for 60 micron band
144	Repeat for 100 micron band
152	PNEARC		Number of Sources in 					4I1
			Confusion Window
			(1 value per band)
156	NID		Number of Positional					I2
			Associations
158	IDTYPE		Type of Object						I1
159	SPARE		1 spare byte						1A1
---- New Record ----
160	CATNO		Catalog Number						I2
162	SOURCE		Source ID						15A1
177	IDTYPE		Source Type/Spectral Class				5A1
182	RADIUS		Radius Vector from SSC		Arcsec			I3
			Position to Association
185	POS		Position Angle from SSC		Degree			I3
			Position to Association
			(E of N)
188	FIELD1		Object Field #1			Catalog			I4
							dependent
192	FIELD2		Object Field #2			Catalog			I4
							dependent
196	FIELD3		Object Field #3			Catalog			I4
							dependent
200-240	Continuation of Associations in Blocks of 40 Bytes
.
.
.

The following are brief descriptions of the individual entries in the table above.

Source Name: NAME, APPNAME

The SSC source name is constructed as for PSC sources and is derived from its position by combining the hours, minutes and tenths of minutes of right ascension and the sign, degrees and minutes of the declination. In obtaining the minutes of right ascension and declination for the name, the positions were truncated. If sources within a field have duplicate positional names, they are distinguished by an appended letter (APPNAME), starting with the letter A. See Source Designations for IRAS Catalogs.

Position: HOUR, MINUTE, SECOND, DSIGN, DECDEG, DECMIN, DECSEC

As in the PSC, positions are given for the equinox 1950.0 and epoch 1983.5. Hours (HOUR) and minutes (MINUTE) of right ascension are given as integers while seconds (SECOND) are rounded to integer deci-seconds. The declination is given as a character sign (DSIGN) followed by integer values of degrees (DECDEG), minutes (DECMIN) and seconds (DECSEC).

Position Angle: ANGLE

The position angle of the major axis of the SSC source error box expressed in degrees East of North.

Flux Density: FLUX(4)

Each of the four wavelengths has a NON-COLOR-CORRECTED flux density in units of Janskys (1 Jy = 1E-25 W m-2 Hz-1). Color correction for any spectral shape is possible. Quoted flux densities are the noise-weighted averages.

Flux Quality: FQUAL (4)

Each flux density measurement is designated high quality, moderate quality, or upper limit (FQUAL = 3, 2, or 1, respectively) based on the prescription discussed in Section III.C of the Explanatory Supplement.

Flux Density Uncertainty: RELUNC(4), TLSNR(4)

Each flux density measurement other than an upper limit has an associated uncertainty expressed in two ways; RELUNC is the uncertainty expressed as a 1 sigma value in units of 100x<n>/<F> (see Section III.C.2). TLSRN is ten times the local signal-to-noise ratio (see Section II.C) as determined from the reference or confirming grid, whichever is least.

Point Source Correlation Coefficient: CC(4)

As discussed in Section III.B of the Explanatory Supplement, SSC sources can have point source correlation coefficients between 70-100%. These are encoded as alphabetic characters with A = 100, B = 99, ..., Z=75-70, one value per band. The quoted correlation coefficients come from the reference or confirming grids, whichever is higher, for high-quality sources.

Flux Density Ratio: TRFLUX(4)

As discussed in Section III.B, SSC sources can have flux density ratios 0.5 < F(c)/F(r) < 2.0, where F(r) and F(c) are the flux densities for the reference and confirming observations, respectively. TRFLUX is the flux density ratio for high-quality sources expressed as 10 x F(c)/F(r).

Position differences: POSDRS12, POSDR12, POSDDS12, POSDD12, ...

The quoted positions of SSC sources are determined from a weighted average of the positions of the confirmed sources in each band with a high-quality flux density (see Section III.C.1). POSDRS12, POSDR12, POSDDS12, and POSDD12 give the sign and amplitude (in arcsec), of the difference in right ascension and declination, respectively, between the final band-merged position and the 12 micron confirmed source position. The succeeding 12 entries repeat the above format for 25, 60, and 100 micron confirmed source component.

Confusion: PNEARC(4)

In regions of high source density, the Pointed Observation source extraction process, as well as the Serendipitous Survey Confirmation and Band Merging processing, can result in degraded positions and incorrectly band-merged sources. PNEARC is 1-(number of confirmed sources in the confusion and band merge window). (See Section III.D.) Any value greater than zero is indicative of potential confusion in the processing and the resulting source information should be examined carefully, e.g., by inspection of the grids in question.

Positional Associations: NID, IDTYPE, CATNO, SOURCE, TYPE, RADIUS, POS, FIELD 1-3

The positional associations, formats, and definitions are done as per the format of the Point Source Catalog, with these exceptions:

1. Positional associations are made with the PSC when SSC and PSC positions agree to within 60". The PSC catalog is assigned catalog number 41.
2. The search box for associations with high precision stellar catalogs, 13 (SAO),15 (Bright Star catalog), and 24 (Two Micron Sky Survey with Improved Positions) is 28" x 180" rather than the 16" x 90" search box used for associations in the PSC.
3. The search radius for associations with the Dearborn catalog is increased to 120".

               Table 2.  Format of Overlapping Fields File

Start	Name		Description			Units			Format
Byte
00	GRID0		Prime Ref. Grid						I5
05	SPARE		1 spare byte						1A1
06	GRID1		Overlapping Field #1,					I5
				Ref. Grid	
11	SPARE		1 spare byte						1A1
12	AOVLP1		Overlapping Sky Coverage	Arcmin^2		I4
16-2			Repeat of 5-15 for Overlapping
			Field #2
17-27			Repeat of 5-15 for Overlapping
			Field #3
.
.
.
60-70			Repeat of 5-15 for Overlapping
			Field #5
71-79	SPARE		9 spare bytes						9A1
---- New Record ----
80-85	SPARE		6 spare bytes						6A1
86-96			Repeat of 5-15 for Overlapping
			Field #6
.
.
.

The quantities in the Overlapping Fields List are as follows:

Prime Reference Grid: GRID0

The grid against which other reference grids are checked for overlapping sky coverage.

First Overlapping Grid: GRID1

The number of the first reference grid with more than 5% overlap with GRID0.

Overlap Area: AOVLP1

Area of overlapping sky coverage between GRID0 and GRID1 in square arcminutes.

The format is repeated for each additional grid overlapping with GRID0. If more than 5 grids overlap with GRID0, they are listed in succeeding records, as necessary; the first six bytes of each of these additional records begins with a string of 6 spaces.

Back to IRAS Serendipitous Survey Catalog Description