Table X.B.1 describes each entry in the catalog tape. Those columns that are also included in the printed version are marked. Each catalog entry requires 160 + NID × 40 bytes of ASCII data where NID is the number of positional associations for each source. In the table the column "Format" refers to the length and type of the (FORTRAN) character field used to read or write each entry. Figure X.B.1 describes the format of the printed version of the catalog.
The tape is written with 80-character (ASCII) logical records and blocked with 256 logical records per physical record so that one can regard the tape as a sequence of card images. The entries are arranged so that the source data fits into two records. Association information requires an additional 40 characters per association and appears in subsequent records, two associations per record. If one assumes an average of two associations per source, then a file for one of the right ascension blocks will require about 10 Mbytes.
|11||HOURS||Right Ascension 1950.||Hours||I2|
|13||MINUTE||Right Ascension 1950.||Minutes||I2|
|15||SECOND1||Right Ascension 1950.||deci-Seconds||I3|
|19||DECDEG||Declination 1950.||Arc Deg||I2|
|21||DECMIN||Declination 1950.||Arc Min||I2|
|23||DECSEC1||Declination 1950.||Arc Sec||I2|
|25||MAJOR1||Uncertainty ellipse major axis||Arc Sec||I3|
|28||MINOR1||Uncertainty ellipse minor axis||Arc Sec||I3|
|31||POSANG1||Uncertainty ellipse position angle||Degree (East of North)||I3|
|34||NHCON1 (<25)||Number of times observed||---||I2|
|36||FLUX1||Averaged non-color corrected flux densities (1 value per band)||Jansky (10-26W m-2 Hz-1)||4E9.3|
|72||FQUAL1||flux density quality. (1 value per band)||---||4I1|
|76||NLRS||Number of significant LRS spectra||---||I2|
|78||LRSCHAR1||Characterization of averaged LRS spectrum.||---||2A1|
|80||RELUNC1||percent relative flux density uncertainties (1 value per band).||---||4I3|
|92||TSNR||ten times the minimum signal-to-noise ratio in each band||---||4I5|
|112||CC1||point source correlation coefficient (1 value per band).||---||4A1|
|116||VAR1||percent Likelihood of Variability||I2|
|118||DISC||Discrepant Fluxes flag (one per band, hex-encoded)||---||A1|
|119||CONFUSE1||Confusion flag (1 flag per band, hex-encoded)||---||A1|
|120||PNEARH1||Number of nearby hours- confirmed point sources||---||I1|
|121||PNEARW1||Number of nearby weeks- confirmed point sources||---||I1|
|122||SES11||Number of seconds-confirmed nearby small extended sources. (1 value per band)||---||4I1|
|126||SES21||Number of nearby weeks-confirmed small extended sources. (1 value per band)||---||4I1|
|130||HSDFLAG1||Source is located in high source density bin. (1 value per band, hex-encoded)||---||A1|
|131||CIRR11||Number of nearby 100 µm only WSDB sources||---||I1|
|132||CIRR21||Spatially filtered 100 µm sky brightness ratio to flux density of point source (see text)||---||I1|
|133||CIRR3||Total 100 µm sky surface brightness||MJy sr-1||I3|
|136||NID1 (<25)||Number of positional associations.||---||I2|
|138||IDTYPE||Type of Object||---||I1|
|139||SPARE||21 spare bytes||---||21A1|
|177||TYPE1||Source Type/Spectral Class||---||5A1|
|182||RADIUS1||Radius Vector from IRAS Source to Association||Arc Sec||I3|
|185||POS||Position Angle from IRAS Source to Association||Degree E of N.||I3|
|188||FIELD12||object field #1 (magnitude/other)||catalog dependent||I4|
|192||FIELD22||object field #2 (magnitude/other)||catalog dependent||I4|
|196||FIELD3||object field #3 (size/other)||catalog dependent||I4|
|200||continuation of associations3|
|-240||in blocks of 40 bytes|
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.
3 CATNO, SOURCE, TYPE, RADIUS, POS, FIELD 1-3 are repeated in blocks of 40 bytes, 2 per logical record, as necessary. The definition and formats of FIELD1-3 depend on the individual catalog in which the association is found. See Table X.B.4.
Figure X.B.1 Explanation of format of printed version of point source catalog.
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 µm. 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 X.B.2). The four bits of that hex digit correspond to the four wavelength bands with bit 0 (Least Significant Bit) for 12 µm, bit 1 for 25 µm, bit 2 for 60 µm and bit 3 for 100 µm. 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 µm would have CONFUSE = 0011 = 3(Hex) while one confused in 25,60 and 100 µm would have CONFUSE = 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. At the end of the section a few remarks relevant only to the printed version of the catalog are given.
|Flag Set in A Particular Band||Resultant Value|
|100 µm (Bit 3)||60 µm (Bit 2)||25 µm (Bit 1)||12 µm (Bit 0)||of Encoded Flag xxxx = HEX=Decimal|
The flux densities have been calculated assuming an intrinsic source energy distribution such that the flux density fv is proportional to v-1. Corrections to other spectral shapes can be made by consulting Section VI.C.
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 indicating saturation has occurred (Table X.B.7a).
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). 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 X.B.7) is set. HSDFLAG is hex encoded by band.
SES2 is the number of weeks-confirmed small extended sources in a given band, located within a 6' in-scan × 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.
CIRR1 gives the number of 100 µm-only WSDB sources located within a ± ½° 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 µm (see (Eq. V.H.2)). Values larger than 4~5 indicate the presence of considerable structure in the 100 µm emission on a ½° scale. A value of 0 indicates that no ½° data were available for the source in question.
CIRR3 is the total surface brightness of the sky surrounding the source in a ½° beam at 100 µm, clipped to exclude values greater than 254 MJy sr-1. Values of CIRR3 greater than 30 MJy sr-1 indicate emission from dust with an appreciable column density. A value of CIRR3 = -1 means that no data were available.
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, 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 (Tables V.H.1, X.B.4).
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° east of north. Three fields (FIELD1-3) have values depending on the catalog in question (Table X.B.4). Typically FlELD1,2 are magnitudes (in decimag) and FIELD3 a size.