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1985iasi.book.....Beichmann+
1988iasi.book.....Beichmann+

Explanatory Supplement for the Machine-Readable Version of the

IRAS FAINT SOURCE CATALOG

|b| > 10 Degrees
Version 2.0

Moshir, M. et al.

1989

Notes to the CD-ROM Machine-Readable Version of the IRAS Faint Source Catalog
The following text is an exerpt from the original "Explanatory Supplement to the IRAS Faint Source Survey, Version 1" (Moshir et al. 1989). Presented here is Chapter V: "The Formats of the FSS Products", section C.1, and Table II.G.6: "Meaning of the Source Association Fields". The text has been altered slightly to accommodate the changes in version 2.0. The formats and fields of the two machine-readable data files of the catalog are adequately described. For further explanation, the original published explanatory supplement should be consulted.

The catalog was received from the Infrared Processing and Analysis Center (IPAC) as two FITS files. These were converted into two ASCII files with the following characteristics:

  1. Data File          Record Length: 240       Number of Records: 173,044
  2. Associations File  Rocord Length:  64       Number of Records: 235,935
The entire original published version of the explanatory supplement (version 1) was received as a set of TeX files. The mentioned sections were extracted and converted to ASCII in order to create this document. The TeX files as received were added to the CD-ROM so that one might have access to a complete copy of the published explanatory supplement. However, note that the data pertains to version 2.0, therefore, an addendum file was created in TeX to outline the changes in the 2.0 version.
Susan Gessner, Space Data and Computing, NASA/GSFC

C.1 The Short Machine-Readable Version of the Faint Source Catalog

The short FSC tape is presented as FITS table data. In order to do this, the associations block has been split out as a separate file. It takes one 6250-bpi tape to hold all of these files for |b| >50 degrees. The FITS table format consists of the following: Specifically, the formats of the files are as follows:
     FILE 1:

	  Block 1 - short header file

	  Blocks 2-10 - FSC_DATA header

	  Blocks 11-END - FSC_DATA

     FILE 2:

	  Block 1 - short header file

	  Blocks 2-4 - FSC_ASSOC header

	  Blocks 5-END - FSC_ASSOC
The short header file is given in Table V.C.1. (in the published version of the explanatory supplement.)

TABLE V.C.4. Format of FSC Data File for Short FSC Tape

_____________________________________________________________________________
Start
Byte  Name       Description                         Units              Format
___________________________________________________________________________
 000  NAME *    Source Name                        _                    12A1
 012  RAHR      Right Ascension 1950               Hour of time           I2
 014  RAMIN     Right Ascension 1950               Minute of time         I2
 016  RASEC *   Right Ascension 1950               deci-Second of time    I3
 019  DECSGN *  Declination Sign                   +/-                    A1
 020  DECDEG    Declination 1950                   Arc Degree             I2
 022  DECMIN    Declination 1950                   Arc Minute             I2
 024  DECSEC *  Declination 1950                   Arc Second             I2
 026  UNCMAJ *  Uncertainty ellipse major axis     Arc Second             I3
 029  UNCMIN *  Uncertainty ellipse minor axis     Arc Second             I3
 032  POSANG *  Uncertainty ellipse position angle Degree (East           I3
						   of North)
 035  NOBS *+   Number of times observed in        _                     4I3
		each band
 047  FNU *+    Flux densities (1 value per        Jansky (10^-26      4E9.3
		band, non-color corrected)         W m-^2 Hz^-1)
 083  FQUAL *+  Flux density quality               _                     4I1
		(1 value per band)
 087  RELUNC +  Percent relative flux density      _                     4I3
		uncertainties (1 value/band)
 099  MINREL *  Minimum percent reliability        _                      I2
 101  MEDSNR *+ SNR in each band                   _                   4E7.1
 129  LOCSNR *+ Local SNR in each band             _                   4E7.1
 157  AREA *+   Number of pixels above             _                     4I3
		threshold in each band
 169  CATNBR *  No. of nearby catalog sources      _                      I2
 171  EXTNBR *+ No. of nearby extractions          _                     4I2
		in each band
 179  CIRRUS *  No. of nearby 100-micron-only      _                      I2
		extractions
 181  CONFUSE * Confusion flag (1 flag/band,       _                      A2
		hex encoded)
 183  NOISCOR + Noise correction factor            _                   4F5.2
		(1 value per band)
 203  NID *     No. of positional associations     _                      I2
 205  IDTYPE    Type of object                     _                      I2
 207  NOISRAT   Ratio 85% to 68% of flux           _                   4F5.3
		distribution (1 value per band)
 227  SPARE                                                             13A1
______________________________________________________________________________
NOTES:
* Quantities listed in microfiche version of catalog
+ In the FITS header, these quantities are suffixed by the wavelength. Example: FNU(4) is given as FNU_12, FNU_25, FNU_60, and FNU_100.

TABLE V.C.5. Format of Association Data for FSC Tape

_____________________________________________________________________________
Start
Byte  Name       Description                         Units            Format
_____________________________________________________________________________
00    NAME *   Source Name                         _                     12A1
12    RECNO *  Record No. in main data table       _                       I6
18    CATNO *  Catalog No.                         _                       I2
20    SOURCE * Source ID                           _                     15A1
35    TYPE *   Source Type/Spectral Class          _                      5A1
40    RADIUS * Radius vector from IRAS             Arc Second              I3
	       source to association
43    POS      Position angle from IRAS            Degree (East            I3
	       source to association               of North)
46    DSTMAJOR Distance from IRAS source to        Arc Second              I3
	       association along the IRAS position
	       error major axis
49    DSTMINOR Distance from IRAS source to        Arc Second              I3
	       association along the IRAS
	       position error minor axis
52    FIELD1 + Object field #1                     Catalog                 I4
	       (magnitude/other)                   dependent
56    FIELD2 + Object field #2                     Catalog                 I4
	       (magnitude/other)                   dependent
60    FIELD3   Object field #3                     Catalog                 I4
	       (magnitude/other)                   dependent
_____________________________________________________________________________
* Quantities listed in printed version of catalog
+ FIELD1 is listed in microfiche version of catalog, except for catalogs 2 and 19, where FIELD2 is listed.

Table V.C.2 gives a sample of the header for the non-association data and Table V.C.3 gives a sample of the header for the association data. Tables V.C.4 (FSC data) and V.C.5 (association data) describe each entry in the short catalog tape. All of this information is contained in the actual FITS headers, but is presented here in an easier-to-read format. Those columns that are also included in the microfiche version are marked. Each catalog entry required 240 bytes of ASCII data for the non-association data and NID x 64 bytes of ASCII data for the association data. In these tables the column "Format" refers to the length and type of the (FORTRAN) character field used to read or write each entry.

The tape is written with 240-character (ASCII) logical records for the non-association data and with 64-character records for the association data. The number of logical records per physical record is 36 for the headers, 12 for the non-association data, and 45 for the association data. These numbers apply to unblocked files only and should be multiplied by the blocking factors for blocked files.

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. 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. 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 flag set at 12 and 25 microns would have a value of 0011=3(Hex) while a flag set at 25, 60 and 100 microns would have a value of 1110=E (Hex). A flag encoded in this manner will be referred to as "hex-encoded by band".

The remainder of this section discusses individual entries in the catalog.

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. This quantity is preceded by the letter `F' to designate a FSC source, and the letter `Z' to designate a Reject File source. The letters `A', `B', `C', etc., are appended to names of sources so close together that they would otherwise have had identical names. Due to the large number of duplicate sources caused by plate overlap, we have changed the convention used in the PSC and eliminated the `A' for the first such source with a duplicate name. Names were uniquely assigned to both catalog and reject file sources, including duplicate sources, with catalog sources named first. An example of a reference to a FSC source is IRAS F12345-6789. Table V.C.6 collects all the various designations for sources in all IRAS catalogs.

    TABLE V.C.6    Source Designations for all IRAS  Catalogs

    __________________________________________________________
    Catalog                                  Source Name
    __________________________________________________________

    Point Source Catalog                     IRAS 12345-6789
    Point Source Reject File                 IRAS R12345-6789
    Small Scale Structure Catalog            IRAS X1234-678
    Serendipitous Survey Catalog             IRAS S12345-678
    Faint Source Catalog                     IRAS F12345-6789
    Faint Source Reject File                 IRAS Z12345-6789
    __________________________________________________________

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).

Position uncertainty: MAJOR, MINOR, POSANG

As discussed in Section II.F.3, the uncertainty in the position for a source depends primarily on its brightness in the various wavelength bands and the number of sightings. The final uncertainty is expressed as an ellipse whose semimajor (MAJOR) and semi-minor (MINOR) axes are the 1-sigma errors 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: NDET

The number of individual detector sightings is given.

Flux Density: FNU(4)

Each of the four wavelengths has a non-color-corrected flux density in units of Janskys (1 Jy = 10^-26 W m^-2 Hz^-1). 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 nu^-1 . Corrections to other spectral shapes can be made by consulting Section VI.C in the Main Supplement or by the table inside the back cover of this Supplement.

Note that the flux density quoted for some sources could be zero if there were not enough data available to derive a good upper limit (see Sections II.F.4 and III.H).

Flux Density Quality: FQUAL(4)

As described in Section II.F.4, a flux-density measurement can be either high quality (FQUAL=3), moderate quality (FQUAL=2) or an upper limit (FQUAL=1).

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 II.F.4 and III.F.

Signal-to-Noise Ratios: MEDSNR(4), LOCSNR(4)

The SNR is calculated in two different ways. The median SNR (MEDSNR) is calculated through the use of a median noise calculated over an area of roughly 15 x 15 arcsec (and corrected by NCF), which is accurate to approximately 8% (see Section III.A.4). This median SNR is referred to simply as SNR elsewhere in this document. The local SNR (LOCSNR) is calculated using the noise for the pixel containing the peak flux density of the source (see Section II.C.4).

Area of source: AREA(4)

The area of each source is calculated as the number of contiguous pixels with flux density above three times the noise after possible rethresholding.

Confusion: CONFUSE, CATNBR, EXTNBR(4)

As described in Section II.F.5, the bandmerger attempted to identify sources that were confused with neighboring sources in one or more bands. The CONFUSE flag is set in a given band if any instance of confusion was present in that band.

Other indicators of possible confusion are given by CATNBR and EXTNBR. CATNBR gives the number of nearby catalog sources within a radius of 6 arcmin. EXTNBR gives for each band the number of extractions within a radius of 6 arcminc.

Cirrus Indicator: CIRRUS

Over nearly the entire sky, portions of the FSS plates are affected by the infrared cirrus. Cirrus can seriously hamper efforts to extract point sources from the data and can also produce structure on a point source scale that can masquerade as true point sources. The CIRRUS flag gives the number of 100 microns- only sources in the extraction database within a radius of 30 arcmin. It is a fairly good discriminant that warns the user that cirrus which contains structure on a point source scale is present in a given region. Values above 2 usually indicate contamination.

Minimum reliability: MINREL

The minimum reliability for a source is the maximum of the reliability calculated individually for each band. See section III.D for more information.

Positional Associations: NID, IDTYPE, CATNO, SOURCE, TYPE, RADIUS, DSTMINOR, DSTMAJOR, POS, FIELD1-3

Much of the utility of the FSC comes from the association of infrared objects with sources known to exist from other astronomical catalogs. As described in Section II.G, 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 64-character decription which is placed in a separate association file in order to conform to the FITS catalog format.

IDTYPE ranges from 1 to 15 and states whether an association was found in an extragalactic catalog (bit 0), a stellar catalog (bit 1), catalogs with other types of objects (bit 2) or in a catalog with mixed types (bit 3). Note that this differs from the convention used in previous IRAS data products where only the total of the association types was given. For example, if associations were found to both an extragalactic catalog and a stellar catalog the IDTYPE was `multiple'. We are now preserving the information as to which type of catalogs were matched.

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 arcseconds. POS is the angle between the vector and the local equatorial meridian expressed in degrees east of north. DSTMAJOR is the distance from the IRAS source to the associated object along the major axis of the positional uncertainty ellipse of the IRAS source and DSTMINOR is the similar distance along the minor axis.

Three fields (FIELD1-3) have values depending on the catalog in question (Table V.C.5). Typically, FIELD1,2 are magnitudes (in decimag) and FIELD3 a size.

TABLE II.G.6 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
		  if Field1 = 2   Field2 and Field3 are V mag [decimag]
				  at max, min
		  if Field1 = 3   Field2 and Field3 are photographic mag
				  [decimag] at max,min
		  if Field1 = 4   Field2 and Field3 are estimated V mag
				  [decimag] at max,min
		  if Field1 = 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 Sky    Type            Blank
    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_o [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 [10^-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 Central 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 [decimag]
		  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-microns sources are possibly
     w/good pos.                   confused, blank otherwise

		  Field1           Right ascension difference (IRC-IRAS )
				   [deciseconds of time]
		  Field2           Declination difference (IRC-IRAS )
				   [arcsec]
		  Field3           0

25 DDO            Type             Blank

		  Field1           -999
		  Field2           -999
		  Field3           0

26 Arp            Type             Blank

		  Field1           -999
		  Field2           -999
		  Field3           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-Cetty    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)
		  Field2           -999
		  Field3           0

32 IRAS Small-    Type             Blank
   Scale Structure

		  Field1           Hex-coded bands
		  Field2           -999
		  Field3           -999

39* OSU           Type            Blank
     Radio

		  Field1          Frequency
		  Field2          Flux [deciJy]
		  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 density [mJy]***
		  Field3          Second SSC flux density

42 PSC II         Type            Blank

		  Field1          Hex-coded PSC bands
		  Field2          First PSC flux density [mJy]***
		  Field3          Second PSC flux density [mJy]

48 Virgo          Type            Class**
     Cluster
     Catalog
		  Field1          B_T  magnitude [decimag]
		  Field2          Heliocentric velocity [km/s]
				  (-999 when not available)
		  Field3          Source size 100 x log D_est(.1 arcsec)

49 Dressel        Type            Blank
     and Condon

		  Field1          -999
		  Field2          -999
		  Field3          -999

50 Asteroids      Type            Blank


		  Field1          -999
		  Field2          First four digits of crossing time
				  [seconds, since 1980.0]
		  Field3          Last four digits of crossing time
_____________________________________________________________________________
* Catalog numbers 33-38 reserved for internal use.
** Source name and type fields were combined to hold spectral type and class (Catalog 40), or object classification (Catalog 48).
*** Flux densities given are the first two measurements in order from 12 to 100 microns.
VV Catalog Flags (Catalog 31)
_________________________________________________________________________

Field1    Explanation

     10   VV 10 has the same coordinates as VV29 in the VV Atlas.
	  The UGC was used to confirm that the coordinate is correct
	  for VV 29 and erronerous for VV 10. The UGC position for
	  VV 10 = TGC 10814 was adopted.

     11   The VV position is substantially different (> 400 arcsec) 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 arcsec.)

   -999   No information given
___________________________________________________________________________