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: 235,935The 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.
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.)
_____________________________________________________________________________ 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:
_____________________________________________________________________________ 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
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.
TABLE V.C.6 Source Designations for all IRAS Catalogs
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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
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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.
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).
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.
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.
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Catalog Field and Meaning
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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
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* Catalog numbers 33-38 reserved for internal use.
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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
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