LAMBDA News
Format of the WSDB and Ancillary Files
[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)
andSES2 = 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.
