IRAS WSDB and Ancillary Files Format

[Adapted from the Explanatory Supplement]

The WSDB is broken up into 20 files, one for each range of ecliptic longitude called a "lune" (see below). Table 1 lists the entries in each WSDB file, their variable types and lengths. A second file for each WSDB file, called the Ancillary File (Table 2) contains additional flags and derived quantities obtained during final product generation. Most of the information in the Ancillary file is the same as that in the Point Source Catalog. Character variables are in ASCII format. All arithmetic quantities are in integer format with the high order byte first.

         Table 1.  The Catalog Working Survey Database (WSDB)
Start
Byte	Name	Description			Units		Type
0 	LUNE	SDAD Lune number		--		I*4
4	BIN	Ecliptic Bin number		--		I*4
8	ELONG	Ecliptic longitude 1950.	1E-8 rad	I*4
12	ELAT	Ecliptic latitude 1950.		1E-8 rad	I*4
16	SCAN	average scan angle with		milli-rad	I*2
		respect to ecliptic meridian
18	SIGY	In-scan Gaussian position	micro-rad	I*2
		uncertainty
20	LZ	Cross-scan uniform		micro-rad	I*2
		position uncertainty
22	SIGZ	Cross-scan Gaussian		micro-rad	I*2
		position uncertainty
24	LRSX	Total number of LRS		--		I*2
		extraction requests
26	KSID	Known Source ID			--		I*2
28	NHCON	Number of hours-		--		I*4
		(<25) confirmed sightings
The following values repeat for each hours-confirmed sighting:
32	FLUX	FLUX(I)=In-band power		1E-16 W m-2	4I*4
48	SIGF	SIGF(I)=Uncertainty		1E-16 W m-2	4I*4
		in FLUX(I)
64	TSNR	TSNR(I)=10x(max SNR)		--		4I*2
72	CORR	Maximum correlation		--		I*4
		coefficient (1 value
		per band)
76	FSTAT	Flux status word		--		I*2
		(1 value per band)
78	DETID	Detector ID Array		--		12I*2
		(4,3) for 4 bands
102	LRSXNO	Number of LRS extraction	--		I*1
		requests
103	DNAME	detector part of		--		I*1
		source name
104	TNAME	deci-UTCS part 			deci-sec	I*4
		of source name
108	CSTAT	Confusion status flags		--		I*4
112-191	Repeats bytes 32-111
192-271	for subsequent hours-
etc.		confirmed sightings

SDAS Lune Number: LUNE

In the data reduction the sky was divided into twenty "lunes" based on ecliptic coordinates. Lune 1 comprises that part of the sky with beta > 60°; lune 2 comprises that sky with beta < -60°. Lunes 3-20 comprise that part of the sky with |beta| <= 60° and ecliptic longitudes, lambda, in 20° wide blocks. Lune 3 extends from 0 < lambda < 20°, lune 4 from 20 < lambda < 40°, etc.

Ecliptic Bin Number: BIN

To aid the data reduction the entire sky was divided into some 40,000 1 sq. deg bins. The bin structure is quite simple in ecliptic coordinates (Fig X.Ap1.1 of the Explanatory Supplement) and an algorithm for generating bin numbers is given in the documentation for the High Source Density Bins file.

Ecliptic Coordinates: ELAT, ELONG

Ecliptic coordiates are given in units of 1E-8 radians in the equinox 1950.

Scan Angle: SCAN

After weeks-confirmation SCAN gives the average scan angle of the focal plane with respect to the south-going local ecliptic meridian.

Positional Uncertainty: SIGY, LZ, SIGZ

As discussed in detail in Section V.D, the position refinement describes the source positional uncertainty in terms of 1 sigma in-scan and cross-scan gaussian uncertainties (SIGY and SIGZ) and a uniform uncertainty (of half-width LZ) whose size depends on the exact paths of the source across the focal plane.

Number of LRS Extractions: LRSX

Each time a source with a signal-to-noise ratio greater than 25 at either 12 or 25 microns transversed the focal plane, the data reduction software automatically triggered a request to extract a spectrum from the Low-Resolution Spectrometer data. The threshold was purposefully set quite low so that sources with weak continua but strong lines could be detected. Many sources with LRSX > 0 will fail to have meaningful spectra and will thus have NLRS = 0.

Known Source ID: KSID

The positions and predicted brightnesses of some 32,000 point sources including SAO stars, IRC objects and asteroids were incorporated into the data reduction software to provide a check on the positional and photometric accuracy of the IRAS sources. Table 3 lists the range of KSID values assigned to sources of various types.

Flux and Flux Uncertainty: FLUX(4), SIGF(4)

Flux and flux uncertainty measurements are given in units of 1E-16 W m-2 for each hours-confirmed sighting. Note that an instrumental flux, not the flux density, is given. In order to convert the instrumental flux to flux density, one must divide the instrumental flux by 13.48, 5.16, 2.58, 1.00 x 1e12 Hz at 12, 25, 60, and 100 microns respectively. The derivation of flux uncertainties and the averaging of the individual hours-confirmed fluxes to give the average value (see AVGFLUX, below) quoted in the catalog is discussed in Section V.H.5 of the Explanatory Supplement.

Signal-to-Noise Ratio: TSNR(4)

If a source is detected (but not necessarily even seconds-confirmed) in a given band, then a value equal to ten times the maximum signal-to-noise ratio (SNR) observed on any detector in that band in the hours-confirmed sighting is retained. In relatively simple parts of the sky the noise estimator used to derive SNR gives reasonable values. In more complex regions near the Galactic plane (see Section V.C.2 of the Explanatory Supplement) the utility of SNR is very limited.

Correlation Coefficient: CORR

The maximum point source correlation coefficient (see Section V.C.4 of the Explanatory Supplement) obtained during a hours-confirmed sighting is retained for each band. The values for each band, expressed as percentages up to a maximum of 100, are encoded into a single integer according to the following algorithm:

    CORR = CC(1) x 2^24 + CC(2) x 2^16 + CC(3) x 2^8 + CC(4)

Flux Status: FSTAT

In each band there is a hierarchy of measurement quality depending on how many times a given source is observed within a given hours-confirmed sighting. FSTAT plays a crucial role in determining whether a source is included in the catalog at all, whether a flux is of high, medium or low quality, and how the flux averaging was performed (Section V.H.5 of the Explanatory Supplement). For the meaning of each FSTAT value refer to Section V.D.8.

The values of FSTAT for the four bands are compressed into a single integer according to the following algorithm:

    FSTAT = FSTAT(1) x 2^12 + FSTAT(2) x 2^8 + FSTAT(3) x 2^4 + FSTAT(4)

Detector ID's: DETID

The identities of all detectors observing a given source on the sightings (up to a maximum of 3 sightings) comprising a given hours-confirmed observation are recorded in the array DETID(I,J). The four bands run from I = 1 to 4 while the three sightings run from J = 1 to 3.

Each value of DETID contains an integer that must be decoded according to the following algorithm to obtain the detectors observing the source:

	DETID(I,J) = D1 x 2^10 + D2 x 2^5 + D3

where detector numbers D1, D2, and D3, range from 1 to 16 within each band. Table 4 lists the correspondence between detector number within a band and the true detector number. The order of detector number is significant as described in V.D.5 of the Explanatory Supplement. It should be emphasized that when three detectors are named in a sighting, indicating the presence of an edge detection, the weakest of the edge detections may not have played any part in the assignment of flux or position.

Detector Name: DNAM, TNAM

Throughout the course of the data processing each hours-confirmed sighting is known by a combination of the first detector measuring the object (DNAME) and the time (in deci-UTCS since 1981, January 1, 0h UT) of that sighting (TNAM).

Confusion Status: CSTAT, PNEARH, PNEARW

At various stages in the reconstruction of a point source attempts are made to recognize (and remedy) the effects of confusion between nearby sources. The confusion status word CSTAT plays an important role in selecting sources to be treated by the "clean-up" processor (Section V.H.2 of the Explanatory Supplement) and in determining which sources to keep in regions of high source density (see Section V.H.6). For a detailed discussion of confusion processing see Section V.D.2. Values of CSTAT and brief descriptions of their meaning are given in Section V.D.8.

The values of CSTAT for each band are encoded into a single integer according to the following algorithm:

    CSTAT = CSTAT(1) x 2^24 + CSTAT(2) x 2^16 + CSTAT(3) x 2^8 + CSTAT(4)

The number of hours and weeks-confirmed point sources within 6' x 4.5' (half-widths) of the quoted source, PNEARH and PNEARW, are encoded into a single byte:

    PNEAR = PNEARW x 2^4 + PNEARH

Cirrus Flags: CIRRUS, CIRR1, CIRR2, CIRR3

The three flags denoting the presence of extended 100 micron emission ("cirrus") as discussed in Section V.H.4 of the Explanatory Supplement, are encoded in two bytes according to the algorithm:

    CIRRUS = CIRR3 x 2^8 + CIRR1 x 2^4 + CIRR2 [sic]

Values of CIRR2 = 0 and CIRR3 = -1 mean no data were available.

Small Extended Source Flags: SES1, SES2

The two small extended source flags for each band discussed in Section V.E.1 of the Explanatory Supplement are encoded into two integers according to the following algorithm:

    SES1 = SES1(1) x 2^12 + SES1(2) x 2^8 + SES1(3) x 2^4 + SES1(4)

and

    SES2 = SES2(1) x 2^12 + SES2(2) x 2^8 + SES2(3) x 2^4 + SES2(4)

Clean up Processors: CLEAN, BRIGHT, ACCEPT, HSDPROC, MISC

In creating the WSDB from the weeks-confirmed data, several processors were applied in order to fix various known problems (see Section V.H of the Explanatory Supplement). These processors set various flags that allow the user to understand what processing occurred. The clean-up processor allowed the weeks-confirmation of various WSDB sources that did not previously have an opportunity to weeks-confirm for purely technical reasons or which were incorrectly split asunder during band merging. The flags set by that processor are described in Table 5; among them are flags indicating saturated fluxes. Optical crosstalk from certain bright objects such as Saturn and IRC+10216 produced a few spurious sources, which were marked for deletion. The byte BRIGHT (Table 6) notes these cases and also contains flags denoting final acceptance (ACCEPT) or rejection of the source in each band.

The flags from the High Source Density processor (HSDPROC, see Section V.H.6) are given in 2 bytes per band (Table 7).

Miscellanous flags are set in MISC (Table 8) and include the presence of flux discrepancies in each band, whether the in-scan positional uncertainties needed to be increased (Section VII.C), and whether the source was accepted in the catalog.

                Table 2.  Ancillary WSDB File
Start
Byte	Name	Description			Units		Type
0	PNEAR	Nearby hours- and		--		I*1
		weeks-confirmed
		neighbors
1	CLEAN	Clean up Processor		--		I*1
		flags
2	SES1	Numer of nearby			--		I*2
		unconfirmed SES
		(4 bands encoded)
4	SES2	Number of nearby		--		I*2
		weeks-confirmed SES
		(4 bands encoded)
6	CIRR1,	Number of 100 micron-		--		I*2
	CIRR2	only WSDB sources,
		spatially filtered
		100 micron emission.
	CIRR3	value of 100 micron half-	M Jy sr-1
		degree beam total
		intensity
8	AVGFLUX	AVGFLUX(I) Averaged flux	1E-16 W m-2	4I*4
		(in-band power)
		in band I
24	AVGUNC	AVGUNC(I) Uncertainty in	1E-16 W m-2	4I*4
		averaged (in-band) flux
		in band I.
40	HSDPROC	HSDPROC(I).  Flages set by	--		4I*2
		the high source density
		processor in band I
48	RA	Right ascension 1950		1E-5 deg	I*4
52	DEC	Declination			1E-5 deg	I*4
56	NAME	source name			--		A*12
68	NLRS	Number of meaningful		--		I*2
		LRS spectra
70	LRSCHAR	characterization of		--		A*2
		LRS spectra
72	BRIGHT	Bright Source Clean up		--		I*1
	ACCEPT	FLAG for catalog sources
		accepted in the catalog
73	VAR	Percent likelihood of		--		I*1
		Variability
74	FQUAL	FLUX Quality flags		--		I*1
		(one per band)
		BIT 0-1, 12 microns
		BIT 2-3, 25 microns, etc.
75	MISC	Miscellaneous Status		--		I*1
		bits, incl. DISC
		ACCEPT,SIGY
		see Table 8
76	LUNE	SDAS Lune number		--		I*4
80	BIN	Ecliptic Bin number		--		I*4
84	ELONG	Ecliptic longitude		1E-8 rad	I*4
88	ELAT	Ecliptic latitude		1E-8 rad	I*4
92	NID	Number of associations		--		I*2
		(<25) to follow
94	IDTYPE	Type of association		--		I*2
96	CATNO	Catalog number			--		I*2
98	SOURCE	Source ID			--		A*15
113	TYPE	Source Type/Spectral Class	--		A*5
118	RADIUS	Position difference		(")		I*2
120	POS	Position angle			deg E of N	I*2
122	FIELD1	object field #1			--		I*2
124	FIELD2	object field #2			--		I*2
126	FIELD3	object field #3			--		I*2
128		continuation of association
-160		in blocks of 32 bytes
etc.

Notes: If NID=0, one blank association field of 32 bytes is written. CATNO,SOURCE,TYPE,RADIUS,POS,FIELD1-3 are repeated in blocks of 32 bytes, 2 per logical record, as necessary. The definition and formats of FIELD1-3 depend on the individual catalog in which the association is found. See Table 5 in the Format of the Point Source Catalog.

                  Table 3.  Known Source ID's
Range		Source Type
1-465		Selected AFGL catalog sources
466-3157	Two Micron Sky Survey Sources
3158-26979	Selected SAO stars (mostly M and K stars)
26980-27497	Selected objects for Low-Resolution Spectrometer
>= 30000	Solar System Objects (asteroids, comets, and outer planets)

                   Table 4.  Detector Number
In-Band		True			In Band		True
Detector	Detector Number		Detector	Detector Number
Number	12 um	25 um	60 um	100 um	Number	12 um	25 um	60 um	100um
1	23	16	08	01	9	47	40	31	56
2	24	17	09	02	10	48	41	32	57
3	25	18	10	03	11	49	42	33	58
4	26	19	11	04	12	50	43	34	59
5	27	20	12	05	13	51	44	35	60
6	28	21	13	06	14	52	45	36	61
7	29	22	14	07	15	53	46	37	62
8	30	39	15	55	16	54	00	38	00

                  Table 5.  CLEAN Bit Assignment
Bit #	Meaning
0-3	Bits 0-3 denote a flux limit derived
	solely from saturated detections.
	Bit 0=12 microns, Bit 1 = 25 microns.
4	Source failed to weeks-confirm with
	another WSDB source in the mini-survey
	region.
5	Source resulted from weeks-confirming
	at least two WSDB sources in the mini-survey
	region.
6	Source failed to weeks-confirm with
	another WSDB entry observed within
	36 hours
7	Source resulted from weeks-confimation
	of two separate WSDB sources observed
	within 36 hours of each other.

                Table 6.  BRIGHT/ACCEPT Bit Assignment
Bit #	Meaning
0	False source generated by nearby bright
	source
1-4	Source satisfies single
	band acceptance criteria
	BIT 1=12 microns, Bit 2=25 microns, etc.
5-7	Source satisfies adjacent
	band acceptance criteria
	BIT 5 = 12 and 25 micron
	BIT 6 = 25 and 60 micron
	BIT 7 = 60 and 100 micron

        Table 7.  HSDPROC High Source Density Processor Flags
 Bit #          Meaning
                Byte 1
0 and 1         00=0 - not processed
                01=1 - low quality flux
                10=2 - medium quality
                11=3 - high quality flux
   2            Band rejected
   3            Band accepted
  4-7           Final reason for rejection
                0000=0 - not rejected
                0001=1 - not weeks-confirmed
                0010=2 - bad flux status
                0011=3 - bad correlation coefficients
                0100=4 - bad confusion status
                0101=5 - inconsistent fluxes
                0110=6 - weaker neighbor
                0111=7 - confused neighbor
                1000=8 - merging problems
                  9-15 - spare

                Byte 2 (Faults with Source)
   0            not weeks-confirmed
   1            bad flux status
   2            bad correlation coefficient
   3            bad confusion status
   4            inconsistent fluxes
   5            weaker neighbor
   6            confused neighbor
   7            merging problems

               Table 8.  MISC Bit Assignment
Bit #	Meaning
0-3     Discrepant Flux found in band.
        BIT 0 = 12 micron,
        BIT 1 = 25 micron, etc.
4,5     SPARE
6       sigma(y) fix (Section VII.C)
7       Source accepted in catalog.

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