[Adapted from the ADC documentation and the Explanatory Supplement.]

The Catalog is contained in one file ordered by right ascension and by declination in case of conflict. For each source, data are shown only for those bands where detections have been found and have survived processing through "weeks confirmation". No upper limits are given where no detections were found; none are given where detections were dropped because of confusion ("cluster analysis"). Absence of data from this Catalog at a given position in a given band does not imply absence of emission, but simply lack of information (see Chapter VI of the reference for a discussion of completeness). On the other hand, flags NEARPS, SES1 and HD, which depend only on position in the sky, are always estimated for all four bands, at the mean position of each source.

In general, the data for each source are organized in three 80-byte records followed by a variable number of association records; Table 1 shows details of the organization. The first two records contain basic parameters and warning flags referring to the band-merged source, whereas the third record is made up of four 20-byte components containing position and quality flags for each of the bands. When present, the 12 micron data are inserted into the first 20 bytes of the record; the 25, 60, and 100 micron data go into the second, third, and last block of 20 bytes in the record, respectively. Quarters corresponding to bands absent from the source are filled with blanks. The fourth and subsequent records contain data on positional associations between the Catalog source and objects in a variety of astronomical catalogs listed in the description of the format of the Point Source Catalog. Each record holds data on two associations, in two 40-byte blocks. All data entries for each source are described below in their order of appearance in Table 1.

As distributed, the catalog is divided into two files. The first is a 240-byte record file containing the 16,740 sources. The second is a 58-byte record file containing the 5,178 associations. The file formats are described below in Tables 1 and 2.


Table 1. Format of the Small-Scale Structure Sources File
Start Byte Name Description Units Format
1 NAME IRAS source name --- 10A1
11 BMFLG Number of bands in source and "band merging" warning flag --- A1 [1]
12 RAHR Right ascension (1950) Hours I2
14 RAMIN Right ascension (1950) Minutes I2
16 RASEC Right ascension (1950) Seconds F4.1
20 DSIGN Declination (1950) --- A1
21 DECDEG Declination (1950) Degrees I2
23 DECMIN Declination (1950) Arcminutes I2
25 DECSEC Declination (1950) Arcseconds I2
27 NH(4) Number of hours-confirmed sightings --- 4A1
31 FLUX(4) Averaged, spatially integrated flux density (no color correction) Jy 4E8.2 [1]
63 XTALK(4) Cross-talk flag --- 4A1 [1]
67 NEARPS(4) Number of near-by weeks-confirmed point sources --- 4A1
71 SES1(4) Number of near-by FISES entries --- 4A1
75 CIR Number of hours-confirmed, 100 micron only point sources --- I2
77 BLANK Four spare bytes --- 4A1
81 HD High source density flag (encoded, one bit per band) --- A1
82 DBLPS Possibility this is a double point source (1 bit per band) --- A1
83 PTSRC Name of IRAS Point Source counterpart and conflict flag --- 12A1
95 PSIZ(4) Size estimate from comparison of FLUX with PTSRC flux Deciarc-minutes 4I3
107 NID Number of associations --- I2
109 IDTYPE Type of objects associated --- I4
113 BLANK 48 spare bytes --- 48A1
161-180 (blank if no 12 micron component)
161 FQLT 12 micron flux quality class --- A1 [1]
162 FCAT 12 micron "final selection" flags --- A1 [1]
163 DRA Right ascension offset from mean position to 12 micron Seconds F6.1
169 DDEC Declination offset from mean position to 12 micron Arcseconds I4
173 UNC 95% confidence diameter for position at 12 micron Deci-arcminutes I3
176 NS Number of individual detections in 12 micron component --- I3
179 BLANK Two spare bytes --- 2A1
181-200 25 micron equivalent of bytes 161-180 (blank if no 25 micron component)
201-220 60 micron equivalent of bytes 161-180 (blank if no 60 micron component)
221-240 100 micron equivalent of bytes 161-180 (blank if no 100 micron component)


Table 2. Format of the Small-Scale Structure Catalog Associations File
Start Byte Name Description Units Format
1 NAME IRAS Source Name --- A10
12 RECNO Rec. Num. of source in data file --- I6
19 CATNO Catalog identifier --- I2
21 SOURCE Object ID in that catalog --- 15A1
36 TYPE Object type in that catalog --- 5A1
41 RADIUS Distance from IRAS source to associated object Arcseconds I3
44 POS Position angle from IRAS source to object Degrees E of N I3 [1]
47 FIELD1 Object data field Nr 1 (magnitude or other) [2] I4 [1]
51 FIELD2 Object data field Nr 2 (magnitude or other) [2] I4 [1]
55 FIELD3 Object data field Nr 3 (magnitude or other) [2] I4 [1]

    [1] This quantity appears with a different format or representation, or is omitted in the printed version of the catalog.

    [2] The definition and units of the quantities in FIELD1-3 depend on the individual catalog in which the association is found. See Table X.B.4 in the Explanatory Supplement.


Table 3. Interpretation of Final Source Selection Flag
Optical Cross-Talk N/M Test [1] Detection Count Flux Threshold Digital Version Printed FCAT Binary Notation
NO MED* PASS PASS B 0 00 00000
NO MED* PASS FAIL F 1 01 00001
NO MED* FAIL PASS F 2 02 00010
NO MED* FAIL FAIL F 3 03 00011
NO LOW PASS PASS F 4 10 00100
NO LOW PASS FAIL F 5 11 00101
NO LOW FAIL PASS F 6 12 00110
NO LOW FAIL FAIL F 7 13 00111
NO HIGH PASS PASS A 8 20 01000
NO HIGH PASS FAIL B 9 21 01001
NO 2/2 PASS PASS B C 30 01100
NO 2/2 PASS FAIL F D 31 01101
NO 2/2 FAIL PASS F E 32 01110
NO 2/2 FAIL FAIL F F 33 01111
YES 2/2 PASS PASS F S X30 11100
YES 2/2 PASS FAIL F T X31 11101
YES 2/2 FAIL PASS F U X32 11110
YES 2/2 FAIL FAIL F V X33 11111

    [1] In the repeatability test, "MED*" indicates that N/M is in the intermediate range (Table IV.B.2) excluding N/M = 2/2; this latter case is indicated by "2/2".

Source Name: NAME
The letter "X" prefixes all names in this Catalog to distinguish them from Point Source Catalog names. The name is then derived from position by combining the hours and minutes from the right ascension with the sign, degrees, and decimal fraction of degrees from the declination. In case of name duplication the letters "A", "B", etc. are appended to the name in order of increasing right ascension, and of increasing declination in case of a tie. See Source Designations for IRAS Catalogs.
"Band Merging" Flag: BMFLG
The "band merging" flag gives the number of bands in which the source has an entry in the third record (regardless of flux quality in these bands), together with indications on the "band merging" processing history for that source. BMFLG=C or D indicates 3 or 4 mutually confirming (section V.E.6 in the Explanatory Supplement) components in the source. BMFLG=I, J, K or L indicates 1, 2, 3 or 4 components in a source having experienced "band merging" complications and having survived the modified "final selection" discussed in IV.B.3.a.
Source position is the simple mean of the positions of all the individual band components in the source regardless of the individual flux quality flags. It is given in equatorial coordinates for the 1950 equinox. Positional accuracy is discussed in V.C.2 of the Explanatory Supplement.
Number of Sightings: NH(4)
The number of survey coverages contributing a sighting to the weeks-confirmed source is given for each band as a single character. The order for this and similar arrays in the Catalog is from 12 microns (subscript = 1) to 100 microns (subscript = 4).
Flux Density: FLUX(4)
An estimate of the spatially integrated flux density from the source is given in Jansky for each band, with three digit precision. This is transformed from the fluxes in the IRAS bands assuming a spectrum with Nu x f(Nu) = constant (see section VI.C of the Explanatory Supplement). To obtain the actual flux density at the nominal wavelength for each band, FLUX must be color corrected. The estimation algorithm is described in sections V.E.3, 4 and 5; calibration in II.C; accuracy is discussed in V.C.1.
Optical Cross Talk Flag: XTALK(4)
This quantity indicates the extent and kind of cross-talk for which each component in the source was flagged. As discussed in IV.B.2a of the Explanatory Supplement, the processor accumulated the number NXT of detections that might have been caused simply by optical cross-talk, along with the number NS of detections. If NXT=0 then XTALK=0 for that band. If NXT > 0, and either (i) (NS-NXT) > 2, or (ii) (NXT/NS) < 2/3 then XTALK=1 for moderate cross-talk. If NXT > 0, and neither (i) or (ii) is true then XTALK=2 for severe cross-talk. If in addition a band component was flagged for cross-talk at the level of "final source selection", then XTALK is increased by 4. Note that the component is given a low quality rating if XTALK > 0.
Near-by Point Sources: NEARPS(4)
This flag gives a count of all weeks-confirmed point sources (regardless of whether or not they are included in the Point Source Catalog) in each band within a 9' radius of the mean position of the SSS Catalog source. NEARPS=1 indicates most often that the emission has been detected as a point source as well as here. Larger values are a warning of possible confusion affecting the source, or an indication that this source combines emission from two or more barely-resolved point sources (see DBLPS below). NEARPS is given as a single character per band, and denoted by a letter when it exceeds 9 ('A' for 10, 'B' for 11, etc.).
Near-by Intermediate Small Extended Sources: SES1(4)
This flag gives a count in each band of all hours-confirmed entries in FISES (section V.E.3 of the Explanatory Supplement) within a 9' radius of the mean position of the source. In a clean sky, SES1 would be equal to NH; larger values implying a higher density of detections, either spurious or due to complex structure, point to areas where "cluster analysis" was active. Large values of SES1 for a band not represented in the source may indicate reliable extended detections discarded in subsequent processing. SES1 appears as a single character per band in the same notation as NEARPS.
Cirrus Indicator: CIR
This cirrus flag gives the number of point source detections at 100 microns only, hours confirmed but not necessarily weeks confirmed, within a 30' radius of the SSS source. Cirrus is rich in structure on all scales, and may supply a 100 micron or a 60 micron component to a source detected at other wavelengths, or may combine with the 100 micron or 60 micron emission from a source and severely compromise its flux measurement. Values of CIR above 6 invite caution in interpreting both 60 and 100 micron detections.
High Source Density Flag: HD
This single character flag denotes whether the source falls in a region of high source density in the sense of Point Source clean-up processing (section V.H.6 of the Explanatory Supplement). This flag was not used in SSS processing, but warns against confusion by pointing out areas where point source density may exceed the resolving capability of the instrument. When the flag is written out in binary notation the least significant bit refers to the 25 micron band, and so on. Values greater than 9 are denoted by letters as for NEARPS.
Double Point Source Flag: DBLPS
This flag indicates the possibility that this Catalog source is the combination of two point sources (see section IV.B.2.e of the Explanatory Supplement for definition). The indication is given for each band, encoded as for HD, with the bit set to 1 when the possibility exists for the corresponding band. This flag is estimated only for bands represented in the source, regardless of the flux quality in these bands.
Coincident Point Source: PTSRC
A small extended source will often trigger the point source detection processor, either because it is still small enough to produce an acceptable fit to the template (bright point sources with low correlation coefficients are examples of this), or because it actually contains one or more point-like components. When an entry from the Point Source Catalog lies within a distance D of the SSS Catalog source position it is identified as a point source counterpart to the SSS Catalog source, and its IRAS name is entered in this column. The distance D used is half the largest value of UNC (section V.C.3 of the Explanatory Supplement) among the bands in the source. When two or more counterpart candidates are found, the nearest one is chosen, and an asterisk precedes PTSRC as a warning. Clearly, the source descriptions here and in the Point Source Catalog are complementary, and neither can be ignored.
Inferred Source Size: PSIZ(4)
An estimate of the source size is given in deci-arcminutes for those bands where the point source counterpart is detected. The estimate is obtained from
PSIZ(i) = FWHM(i) x [SSSFLUX(i)/PTSRCFLUX(i)]^(1/2)
where FWHM(i) is the full width at half maximum of a point source in band i, namely 0.82', 0.84', 1.44', and 3.14', respectively, at 12, 25, 60, and 100 microns; SSSFLUX and PTSRCFLUX are the fluxes in the two catalogs. See V.B.1 and V.C.3 of the Explanatory Supplement for details and a discussion of accuracy.
Positional Associations: NID, IDTYPE
Positional associations between objects in the Small-Scale Structure Catalog and objects in astronomical catalogs were obtained following the same strategy used for point sources (see the format of the Point Source Catalog). The only difference is that the search radius around sources in this Catalog is never less than 120". NID is the total number of matches found. IDTYPE ranges from 1 to 4 to indicate an association found in an extraglactic catalog (1), a stellar catalog (2), other catalogs (3), or matches in multiple types of catalogs (4). Each record starting with the fourth data record for the source contains two of these blocks.
Flux Quality Flag: FQLT
This is the quality class assigned to the band component by the scheme described in Chapter IV and Table IV.A.1 of the Explanatory Supplement. High, intermediate and low qualities are denoted, respectively, by A, B, and F. Starting with this flag, data for each band appear separately in the corresponding quarter of the third data record for the source.
Final Catalog Selection Flags: FCAT
The results of the three main stages of "final selection" are presented in this flag which appears as a single character ranging from 0 to V (Table 3 and section VII.B of the Explanatory Supplement). When FCAT is written out in binary notation, the least significant bit indicates the result of the flux test (IV.B.2.d), and is set if failed; the next bit refers to the detection count test (IV.B.2.c), and is set if failed. The next two bits refer to the repeatability test (IV.B.2.b), and signal one of four possible outcomes: 00 for intermediate values of N/M except N/M = 2/2; 01 for low N/M; 10 for high N/M; and 11 for N/M = 2/2 (Table IV.B.3 of the Explanatory Supplement). The most significant bit in FCAT is set if the detection is flagged for cross-talk of any kind (IV.B.2.a). Table 3 shows all possible values of FCAT, their representation in the file, and their meaning.
Right Ascension Offset: DRA
This gives in seconds the amount to add to the mean right ascension of the source (shown in the first record) to obtain the right ascension measured for the emission in this band.
Declination Offset: DDEC
This gives in arcseconds the amount to add to the mean declination of the source (shown in the first record) to obtain the declination measured for the emission in this band.
Positional Uncertainty from Intensity Distribution: UNC
The second moments about major and minor axes of the roughly-modeled intensity distribution are estimated as explained in V.E.3 of the Explanatory Supplement. UNC is their geometric mean, given as a diameter in deci-arcminutes. Because of the coarse grid used in the definition, UNC is best interpreted as a positional uncertainty, namely the 95% confidence diameter for the position in this band.
Number of Detections: NS
This total number of seconds-confirmed detections in the source is accumulated through "cluster analysis" and "weeks confirmation", and includes detections that failed to seconds-confirm because of a failed detector.
For each match in Table 5 in the discussion of the format of the Point Source Catalog, CATNO is the number identifying that catalog. SOURCE is the name of the object in that catalog, and TYPE its character or spectral or morphological type if available. RADIUS is the distance in arcseconds from the IRAS position to the associated object. POS is the position angle measured in degrees East of North of the direction from the IRAS source to the associated object. FIELD1-3 carry values depending on the catalog in question (Table X.B.4 of the Explanatory Supplement). Typically FIELD1 and FIELD2 contain magnitudes in decimag, and FIELD3 a size in arcseconds.