IRAS Point Source Catalog - Format Description

[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').