LAMBDA News
Format of the Point Source Catalog
[Adapted from the Explanatory Supplement]
The catalog is divided into two files. The first contains the 252,889 sources arranged in order of increasing right ascension and occupies 37.5 Mbyte. The second contains records of 142,228 positional associations and is 7.5 Mbyte long. Tables 1 and 2 describe each entry in the files. In the tables the column "Format" refers to the length and type of the (FORTRAN) character field used to read or write each entry.
In general, for quantities that have a value in each wavelength band, subscripts or array indices range from 1 to 4 and refer, respectively, to 12, 25, 60 and 100 microns.
Hex Encoding. A number of the flags
discussed below have values in each of the four wavelength bands. For
compactness these are encoded into a single base-16 (Hex) digit (values
0-F) in the following manner (Table 3). The four bits of the hex
digit correspond to the four wavelength bands with bit 0 (Least Significant
Bit) for 12 microns, bit 1 for 25 microns, bit 2 for 60 microns and
bit 3 for 100 microns. The presence of a flag in a band is denoted
by setting its bit to 1. Thus a source with a particular flag, e.g.
CONFUSE, set at 12 and 25 microns would have CONFUSE = 0011 = 3 (Hex)
while one confused in 25, 60 and 100 microns would have CONFUSE =
1110 = E (Hex). A flag encoded in this manner is referred to
as "hex-encoded by band".
Table 1. Format of Point Source Catalog Data File
Start
Byte Name Description Units Format
00 NAME [1] Source Name --- 11A1
11 HOURS Right Ascension 1950. Hours I2
13 MINUTE Right Ascension 1950. Minutes I2
15 SECOND [1] Right Ascension 1950. deci-Seconds I3
18 DSIGN [1] Declination Sign ± A1
19 DECDEG Declination 1950. Arc Deg I2
21 DECMIN Declination 1950. Arc Min I2
23 DECSEC [1] Declination 1950. Arc Sec I2
25 MAJOR [1] Uncertainty ellipse Arc Sec I3
major axis
28 MINOR [1] Uncertainty ellipse Arc Sec I3
minor axis
31 POSANG [1] Uncertainty ellipse Degrees I3
position angle (East of
North)
34 NHCON [1] Number of times observed --- I2
(<25)
36 FLUX [1] Averaged non-color corrected Jansky 4E9.3
flux densities (1 value per (1.0E-26 W/m**2/Hz)
band)
72 FQUAL [1] flux density quality. --- 4I1
(1 value per band)
76 NLRS Number of significant LRS --- I2
spectra
78 LRSCHAR [1] Characterization of averaged --- 2A1
LRS spectrum.
80 RELUNC [1] percent relative flux density --- 4I3
uncertainties (1 value
per band).
92 TSNR ten times the minimum signal- --- 4I5
to-noise ratio in each band
112 CC [1] point source correlation --- 4A1
coefficient (1 value
per band).
116 VAR [1] percent Likelihood of I2
Variability
118 DISC Discrepant Fluxes flag --- A1
(one per band, hex-encoded)
119 CONFUSE [1] Confusion flag (1 flag --- A1
per band, hex-encoded)
120 PNEARH [1] Number of nearby hours- --- I1
confirmed point sources
121 PNEARW [1] Number of nearby weeks- --- I1
confirmed point sources
122 SES1 [1] Number of seconds-confirmed nearby --- 4I1
small extended sources.
(1 value per band)
126 SES2 [1] Number of nearby weeks- --- 4I1
confirmed small extended
sources.
(1 value per band)
130 HSDFLAG [1] Source is located in high --- A1
source density bin.
(1 value per band, hex-encoded)
131 CIRR1 [1] Number of nearby 100 micron --- I1
only WSDB sources
132 CIRR2 [1] Spatially filtered 100 micron --- I1
sky brightness ratio to flux
density of point source
(see text)
133 CIRR3 Total 100 micron sky MJy/sr I3
surface brightness
136 NID [1] Number of positional --- I2
(<25) associations.
138 IDTYPE Type of Object --- I1
140 MHCON Possible number of HCONs --- I2
142 FCOR Flux correction factor applied --- 4I4
(times 1000, 1 value per band)
158 SPARE 3 Spare blanks --- 3A1
Table 2. Format of Point Source Associations File
Start
Byte Name Description Units Format
00 NAME IRAS source name --- A11
11 RECNO Record Number of source in data file --- I6
18 CATNO [1] Catalog number --- I2
20 SOURCE [1] Source ID --- 15A1
35 TYPE [1] Source Type/Spectral Class --- 5A1
40 RADIUS1 Radius Vector from IRAS Arc Sec I3
Source to Association
43 POS Position Angle from IRAS Degrees E I3
Source to Association of N.
46 FIELD1 [2] object field #1 catalog I4
(magnitude/other) dependent
50 FIELD2 [2] object field #2 catalog I4
(magnitude/other) dependent
54 FIELD3 object field #3 catalog I4
(size/other) dependent
[1] Quantities listed in printed version of catalog.
[2] FIELD1 is listed in printed version of catalog, except for catalogs 2
and 19, where FIELD2 is listed.
Table 3. Meaning of Hex Encoded Flags
Flag Set in A Particular Band (microns) Resultant Value
100 60 25 12 of Encoded Flag
(Bit 3) (Bit 2) (Bit 1) (Bit 0) xxxx = HEX = Decimal
0 0 0 0 0000 = 0 = 0
0 0 0 1 0001 = 1 = 1
0 0 1 0 0010 = 2 = 2
0 0 1 1 0011 = 3 = 3
0 1 0 0 0100 = 4 = 4
0 1 0 1 0101 = 5 = 5
0 1 1 0 0110 = 6 = 6
0 1 1 1 0111 = 7 = 7
1 0 0 0 1000 = 8 = 8
1 0 0 1 1001 = 9 = 9
1 0 1 0 1010 = A = 10
1 0 1 1 1011 = B = 11
1 1 0 0 1100 = C = 12
1 1 0 1 1101 = D = 13
1 1 1 0 1110 = E = 14
1 1 1 1 1111 = F = 15
- Source Name: NAME
- The IRAS source name 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. The letters 'A','B','C', etc. are appended to names of sources so close together that they would otherwise have had identical names. Names were uniquely assigned to both Catalog and Point Source Reject Catalog sources, with Catalog sources receiving letters first. See Source Designations for IRAS Catalogs.
- Position: HOURS,MINUTE,SECOND,DSIGN,DECDEG,DECMIN,DECSEC
- Positions are given for the equinox 1950.0, and epoch 1983.5. Hours (HOURS) and minutes (MINUTE) of right ascension are given as integers while seconds (SECOND) are rounded to integer deciseconds. The declination is given as a character sign (DSIGN) followed by integer values of degrees (DECDEG), minutes (DECMIN) and seconds (DECSEC). Values of 60 seconds are given when the truncated minutes (given here) disagree with the minutes in the rounded position.
- Position Uncertainty: MAJOR, MINOR, POSANG
- As discussed in Section VII.B.2, the uncertainty in the position for a source depends on its brightness in the various wavelength bands, its path across the focal plane and the number of sightings. The final uncertainty after position refinement is expressed as a 95% confidence uncertainty ellipse (see Section V.D.9) whose semi-major (MAJOR) and semi-minor (MINOR) axes are given in seconds of arc. The orientation (POSANG) of the ellipse on the sky is expressed in terms of the angle between the major axis of the ellipse and the local equatorial meridian. It is expressed in degrees east of north.
- Number of Sightings: NHCON
- The number of hour-confirmed sightings is given. This number of flux entries can be found in the WSDB.
- Flux Density: FLUX(4)
- Each of the four wavelengths has a non-color-corrected flux density in units of Janskys, (1 Jy = 1.0E-26 W m-2 Hz-1). The quoted value is an average of all the hours-confirmed sightings as obtained by the prescription described in Section V.H.5. The quality of each flux density is designated by FQUAL (see below). The flux densities have been calculated assuming an intrinsic source energy distribution such that the flux density f(Nu) is proportional to 1/Nu. Corrections to other spectral shapes can be made (see the description of color correction). The flux densities for sources so bright that they saturated the analog-to-digital converter on every sighting are lower limits based on the brightest value recorded. The uncertainties are given as ten times the quoted flux density and a flag is set in the CLEAN bits of the corresponding entry in the Ancillary Working Survey Database entry indicating saturation has occurred.
- Signal-to-Noise Ratio: TSNR(4)
- The signal-to-noise ratio given for an individual hours-confirmed sighting is the highest value of the detections comprising that sighting (Section V.C.2). The values quoted in the catalog are ten (10) times the minimum of the signal-to-noise ratios for the various sightings (HCONs) of the source. A value is given for each wavelength band with a high or moderate quality measurement and for those upper limits coming from a non- seconds-confirmed detection. Values of TSNR greater than 30,000 are given as 30,000.
- Source Variability: VAR
- VAR is the percent probability (0-99) that a source is variable based on an analysis of the 12 and 25 micron flux densities and their uncertainties (see Section V.H.5). The value "-1 " indicates that the source was not examined for variability.
- Discrepant Fluxes: DISC(4)
- The DISC flag indicates whether any one of the fluxes in a given band disagrees with others in that band, hex-encoded by band (Section V.H.5).
- Flux Density Quality: FQUAL(4)
- As described in Section V.H.5, a flux density measurement can be either high quality (FQUAL=3), moderate quality (FQUAL=2) or an upper limit (FQUAL=1).
- Low-Resolution Spectra: NLRS,LRSCHAR
- The Low-Resolution Spectrometer obtained 8-22 micron spectra of bright 12 and 25 micron sources (Chapter IX of the Explanatory Supplement). NLRS gives the number of statistically meaningful spectra available for the source. LRSCHAR gives a short characterization of the nature of the spectrum (Table IX.D.1 of the Explanatory Supplement).
- Flux Density Uncertainties: RELUNC (4)
- Each flux density measurement other than an upper limit has an associated uncertainty expressed as a 1 Sigma value in units of 100 x [Delta f(Nu)/f(Nu)]. Uncertainties are discussed in Sections V.H.5. and VII.D.2. of the Explanatory Supplement.
- Point Source Correlation: CC(4)
- The point source correlation coefficient can have values between 87-100%. These are encoded as alphabetic characters with A=100, B=99... N=87, one value per band. The value quoted is for the highest correlation coefficient seen for that source on any sighting.
- Confusion: CONFUSE,PNEARN,PNEARW,HSDFLAG
- As described in Section V.D.2 of the Explanatory Supplement, a great
deal of care went into trying to untangle instances of confusion
between neighboring sources. In parts of the sky where the source
density is low, confusion processing was sometimes able to separate
sources that are quite close together. The CONFUSE flag is set if two
or more sightings of the source in a given band had confusion status
bits set, indicating confusion in the seconds-confirmation or band-merging
processes. This flag is hex-encoded by band. Other indicators of
possible confusion are given by PNEARN and PNEARW which are,
respectively, the numbers of hours- confirmed and weeks-confirmed point
sources located within a 4.5' cross- scan and 6' in-scan (half-widths)
window centered on the source. Values larger than 9 are given as 9.
Regions of high source density received special processing to
improve the reliability of the quoted sources (see Section V.H.6 of
the Explanatory Supplement). The regions are band-dependent. If a
particular band of a given source went through high source density
processing, then the appropriate bit in HSDFLAG (Table 4) is set.
HSDFLAG is hex encoded by band.
Table 4. 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 - Small Extended Sources: SES1(4),SES2(4)
- SES1 is the number of seconds-confirmed, small extended source detections in a given band found within a window centered on the source. The size of the window is 6' in-scan x 4.5' cross-scan (half-widths). As described in Sections V.H.3-4 and VII.H.1 of the Explanatory Supplement, values of SES1 greater than 1 should caution the user that significant extended structure may exist in the region and that the source in question may be a point-source like piece of a complex field. SES2 is the number of weeks-confirmed small extended sources in a given band, located within a 6' in-scan x 4.5' cross-scan window (half-width) centered on the source. SES2 greater than 0 means that the point source flux measurement should be treated with caution as the source in question may, in fact, be extended. The flux quoted in the catalog of small extended sources may provide a better value for the source.
- Cirrus Indicators: CIRR1,CIRR2,CIRR3
- Over a large range of Galactic latitudes the infrared sky at 100
microns is characterized by emission from interstellar dust on a wide
range of angular scales. The so-called "infrared cirrus" can seriously
hamper efforts to extract point source detections from the data. To
aid the user in interpreting the quoted 100 micron measurements three
quantities have been established (Sections V.H.4 and VII.H of the
Explanatory Supplement). CIRR1 gives the number of 100 micron-only
WSDB sources located within a 0.5° x
0.5° degree box in ecliptic coordinates centered on the source. The
sources included in this count are the weeks-confirmed sources prior
to high source density region processing (if applicable) plus those
sources hours-confirmed but not weeks-confirmed. Values of CIRR1
greater than 3 may indicate contamination by cirrus with structure
on the point source size scale.
CIRR2 gives a cirrus indication on a larger scale than CIRR1 and compares a "cirrus flux" with the source flux at 100 microns (see Eq. V.H.2 of the Explanatory Supplement). Values larger than 4-5 indicate the presence of considerable structure in the 100 micron emission on a 0.5° scale. A value of 0 indicates that no 0.5° data were available for the source in question.
CIRR3 is the total surface brightness of the sky surrounding the source in a 0.5° beam at 100 microns, clipped to exclude values greater than 254 MJy/sr. Values of CIRR3 greater than 30 MJy/sr indicate emission from dust with an appreciable column density. A value of CIRR3 = 255 means that no data were available.
- Positional Associations: NID, IDTYPE, CATNO, SOURCE, TYPE, RADIUS, POS, FIELD1-3
- Much of the utility of the IRAS catalog comes from the association of
infrared objects with sources known to exist from other astronomical
catalogs. As described in Section V.H.9 of the Explanatory Supplement,
a large number of catalogs have been searched for positional matches.
The total number of matches found is given by NID. Each match results in
a forty-character description (2 per record). IDTYPE ranges from 1 to 4
and states whether an association was found in an extragalactic
catalog (1), a stellar catalog (2), other catalogs (3), or matches in
multiple types of catalogs (4).
CATNO is the number of the catalog in which the match was found (Table 5).
SOURCE is the name of the object in that catalog and TYPE its character or spectral type, if available. A vector is drawn from the IRAS position to the associated object.
RADIUS is the length of that vector in arc seconds.
POS is the angle between the vector and the local equatorial meridian expressed in degrees east of north.
Three fields (FIELD1-3) have values depending on the catalog in question (Table 5). Typically FlELD1,2 are magnitudes (in decimag) and FIELD3 a size.
Table 5. Meaning of the Source Association Fields
Catalog Field and Meaning*
1 GCVS Type Blank
Field1 = Code gives meaning for Fields 2-3
if Field1 = 1 Field2 and Field3 are B mag [decimag] at
max,min
= 2 Field2 and Field3 are V mag [decimag] at
max,min
= 3 Field2 and Field3 are photographic mag
[decimag] at max,min
= 4 Field2 and Field3 are estimated V mag
[decimag] at max,min
= 5 Field2 is 999 and Field3 is 0
------------------------------------------------------------------------------
2 Dearborn Type Blank
Obs.
Field1 Code for Field2 (1,2)
Field2 if Field1 is 1, Field2 is red magnitude
[decimag]
if Field1 is 2, Field2 is 999
Field3 0
------------------------------------------------------------------------------
3 Revised Type Blank
AFGL
Field1 Magnitude at 4.2 microns [decimag]
Field2 Magnitude at 11 microns [decimag]
Field3 Magnitude at 27 microns [decimag]
------------------------------------------------------------------------------
4 2-Micron Type Blank
Sky Survey
Field1 K magnitude [decimag]
Field2 I magnitude [decimag]
Field3 0
------------------------------------------------------------------------------
5 Globules Type Blank
(Wesselius)
Field1 999
Field2 Minimum diameter [arcsec]
Field3 Maximum diameter [arcsec]
------------------------------------------------------------------------------
6 R C 2 Type Blank
Field1 Harvard V magnitude [decimag]
Field2 B(T) [decimag]
Field3 D(0) [arcsec]
------------------------------------------------------------------------------
7 Stars with Type Blank
em. lines
Field1 V magnitude [decimag]
Field2 999
Field3 0
------------------------------------------------------------------------------
8 Equatorial Type Blank
IR Cat.
Field1 Flux density [1.0E-16 W/cm**2/micron]
at 2.7 microns
Field2 999
Field3 0
------------------------------------------------------------------------------
9 UGC Type Blank
Field1 Zwicky magnitude [decimag]
Field2 Minimum diameter [arcsec] in B
Field3 Maximum diameter [arcsec] in B
------------------------------------------------------------------------------
10 MCG Type Blank
Field1 999
Field2 Minimum diameter [arcsec] in B
Field3 Maximum diameter [arcsec] in B
------------------------------------------------------------------------------
11 Strasbourg Type Blank
Planetary Nebulae
Field1 V magnitude of Nebula [decimag]
Field2 B magnitude of Center Star [decimag]
Field3 Minimum diameter of Nebula [arcsec]
------------------------------------------------------------------------------
12 Zwicky Type Blank
Field1 Zwicky magnitude [decimag]
Field2 999
Field3 0
------------------------------------------------------------------------------
13 SAO Type Spectral Type
Field1 V magnitude [decimag]
Field2 p(g) magnitude [decimag]
Field3 0
------------------------------------------------------------------------------
14 ESO/ Type First 3 characters of object type
Uppsala
Field1 B magnitude [decimag]
Field2 Maximum diameter [arcsec]
Field3 Minimum diameter [arcsec]
------------------------------------------------------------------------------
15 Bright Type Spectral Type
Stars
Field1 V magnitude [decimag]
Field2 B-V [centimag]
Field3 U-B [centimag]
------------------------------------------------------------------------------
16 Suspected Type Spectral Information
Var.
Field1 V magnitude at maximum [decimag]
Field2 999
Field3 0
------------------------------------------------------------------------------
17 Carbon Type Spectral Type (May be truncated)
Stars
Field1 p(g) magnitude [decimag]
Field2 V magnitude [decimag]
Field3 I magnitude [decimag]
------------------------------------------------------------------------------
18 Gliese Type Spectral Type (May be truncated)
Field1 V magnitude [decimag]
Field2 B-V magnitude [millimag]
Field3 U-B magnitude [millimag]
------------------------------------------------------------------------------
19 S Stars Type Blank
Field1 p(g) magnitude [millimag]
Field2 V magnitude [decimag]
Field3 I magnitude [decimag]
------------------------------------------------------------------------------
20 Parkes HII Type Blank
Survey
Field1 999
Field2 Minimum diameter [arcsec]
Field3 Maximum diameter [arcsec]
------------------------------------------------------------------------------
21 Bonn HII Type Blank
Survey
Field1 Flux density at 4.875 GHz (Jy)
Field2 Diameter [arcsec]
Field3 0
------------------------------------------------------------------------------
22 Blitz Type Blank
Field1 Diameter [arcsec]
Field2 V(co) [Km/s]
Field3 Peak T(A) [degrees K]
------------------------------------------------------------------------------
23 OSU Type Blank
Field1 999
Field2 999
Field3 Diameter [arcsec]
------------------------------------------------------------------------------
24 IRC Type C if 2.2 micron sources are possibly
confused, w/good pos. blank otherwise
Field1 Right ascension difference (IRC-IRAS)
[deciseconds of time]
Field2 Declination difference (IRC-IRAS)
[seconds of arc]
Field3 0
------------------------------------------------------------------------------
25 DDO Type Blank
Field1 999
Field2 999
Field3 0
------------------------------------------------------------------------------
26 Arp Type Blank
Field1 999
Field2 999
Field 0
------------------------------------------------------------------------------
27 Markarian Type Blank
Field1 999
Field2 999
Field3 0
------------------------------------------------------------------------------
28 Strong Type Object type (GAL or QSO)
5 GHz
Field1 V magnitude [decimag]
Field2 5 GHz flux density [deciJy]
Field3 0
------------------------------------------------------------------------------
29 Veron- Type Object classification
Veron
Field1 V magnitude [decimag]
Field2 Redshift x 1000
Field3 0
------------------------------------------------------------------------------
30 Zwicky Type Blank
8 Lists
Field1 999
Field2 999
Field3 0
------------------------------------------------------------------------------
31 VV Type Blank
Field1 Special flag, (see below) 999 otherwise
Field2 999
Field3 0
------------------------------------------------------------------------------
32 IRAS Small Type Blank
Scale Structure
Field1 Hex coded bands
Field2 Blank
Field3 Blank
------------------------------------------------------------------------------
39 OSU Radio Type Blank
Field1 Frequency
Field2 Flux (deci Jy)
Field3 0
------------------------------------------------------------------------------
40 Michigan Type Class**
Spectral
Field1 Mag (decimag)
Field2 HD number (low byte)
Field3 HD number (high byte)
------------------------------------------------------------------------------
41 Serendipitous Type Blank
Survey
Field1 Hex coded SSC bands
Field2 First SSC flux (mJy)
Field3 Second SSC flux
------------------------------------------------------------------------------
Catalog numbers 33-38 are reserved for internal use.
** Source name and type fields were combined to hold spectral type and class.
VV Catalog Flags (Catalog 31)
FIELD1 Explanation
10 VV 10 has the same coordinates as VV 29 in the VV Atlas. The
UGC was used to confirm that the coordinate is correct for VV
29 and erroneous for VV 10. The UGC position for VV 10 = UGC
10814 was adopted.
11 The VV position is substantially different (>400") from
positions for the object in other catalogs. The VV position
has been assumed to be in error because two or more other
catalogs agree on a different position. The UGC position has
been adopted.
12 Same as for 11, but the OSU position has been adopted.
13 The position in the VV Atlas, and the position listed for the
VV object in the OSU are in disagreement. The true position
has been established to be close to that of the OSU by the use
of overlay transparencies on the POSS. The OSU position has
been adopted.
14 Same as for 13, but the OSU position is not very good either,
so a new position has been measured (accurate to about 1').
