The information about infrared point sources is presented in increasing detail, progressing from the printed volumes to the tape version of the catalog to the detailed description of the observational and processing history of each source in a file known as the Working Survey Data Base (WSDB) augmented by its ancillary file. The printed version (Section X.B.2) is intended for users at the telescope or at institutions without computerized information retrieval systems. The catalog tape (Section X.B. 1) is intended for astronomers desiring to make statistical studies and to search the catalog for large numbers of sources. The WSDB and ancillary file (Section X.B.3) are meant to give the sophisticated researcher all the available data on any given source such as its brightness on each hours-confirmed sighting, the detectors involved and the details of the data reduction such as confusion with neighboring sources.
Another catalog available only in machine readable form lists the WSDB entries for all sources that failed one or more of the confirmation and confusion criteria and were not, thus, included in the main catalog. This file of REJECTED sources includes spurious objects, including: processing failures, space debris, asteroids and comets, and celestial sources that, due to incompleteness at faint levels or to variability, failed to achieve the minimum criterion of two hours-confirmed sightings. In regions of high source density the file includes sources rejected by the more severe criteria for reliability applied there (Section V.H.6). Caveat emptor.
B. 1 The Machine Readable Version of the Point Source Catalog
The point source catalog tape is divided into six individual files, covering the range 0 to 24 hr in right ascension in blocks of four hours each. Each file contains from 20,000 to 90,000 sources arranged in order of increasing right ascension. Each of the six catalog files is preceded by a file containing a single 80-character ASCII record which lists the date and version number of the catalog. Thus to read the entire catalog one must read sequentially through 12 files, six containing the data and six containing dates and version numbers.
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
X-2
Table X.B.1 Format of Point Source Catalog Tape
Start
Byte Name Description Units Format
00 NAME1 Source Name --- 11A1
11 HOURS Right Ascension 1950. Hours I2
13 MINUTE Right Ascension 1950. Minutes I2
15 SECOND1 Right Ascension 1950. deci-Seconds I3
18 DSIGN1 Declination Sign ± A1
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 Arc Sec I3
major axis
28 MINOR1 Uncertainty ellipse Arc Sec I3
minor axis
31 POSANG1 Uncertainty ellipse Degree I3
position angle (East of
North)
34 NHCON1 Number of times observed --- I2
(<25)
36 FLUX1 Averaged non-color corrected Jansky 4E9.3
flux densities (1 value per (10-26W m-2 Hz-1)
band)
72 FQUAL1 flux density quality. --- 4I1
(1 value per band)
76 NLRS Number of significant LRS --- I2
spectra
78 LRSCHAR1 Characterization of averaged --- 2A1
LRS spectrum.
(---------------new record--------------)
80 RELUNC1 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 CC1 point source correlation --- 4A1
coefficient (1 value
per band).
116 VAR1 percent Likelihood of I2
Variability
118 DISC Discrepant Fluxes flag --- A1
(one per band, hex-encoded)
119 CONFUSE1 Confusion flag (1 flag --- A1
per band, hex-encoded)
120 PNEARH1 Number of nearby hours- --- I1
confirmed point sources
121 PNEARW1 Number of nearby weeks- --- I1
confirmed point sources
X-3
Table X.B.1 Format of Point Source Catalog Tape (Continued)
Start
Byte Name Description Units Format
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 µm --- I1
only WSDB sources
132 CIRR2 1 Spatially filtered 100 µm --- I1
sky brightness ratio to flux
density of point source
(see text)
133 CIRR3 Total 100 µm sky MJy sr-1 I3
surface brightness
136 NID 1 Number of positional --- I2
<25) associations.
138 IDTYPE Type of Object --- I1
139 SPARE 21 spare bytes --- 21A1
(---------------new record--------------)
160 CATN0 1 Catalog number --- I2
162 SOURCE1 Source ID --- 15A1
177 TYPE1 Source Type/Spectral Class --- 5A1
182 RADIUS1 Radius Vector from IRAS Arc Sec I3
Source to Association
185 POS Position Angle from IRAS Degree E I3
Source to Association of N.
188 FIELD1 2 object field #1 catalog I4
(magnitude/other) dependent
192 FIELD2 2 object field #2 catalog I4
(magnitude/other) dependent
196 FIELD3 object field #3 catalog I4
(size/other) dependent
200 continuation of associations 3
-240 in blocks of 40 bytes
etc.
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.
X-4
of two associations per source, then a file for one of the right ascension blocks will require about 10 Mbytes.
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.
Table X.B.2 Meaning of Hex Encoded Flags
Flag Set in A Particular Band Resultant Value
100 µm 60 µm 25 µm 12 µm 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,° 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 reject file sources, with catalog sources receiving letters first.
X-6
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° (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° east of north
Number of Sightings: NHCON
The number of hour-confirmed sightings is given. This number of flux entries will 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, (1JY =10-26 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 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).
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 µm flux densities and their uncertainties (see Section V.H.5). The value "-1 " indicates that the source was not examined for variability.
X-7
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 µm spectra of bright 12 and 25 µm sources (Chapter IX). 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). All of the LRS spectra are available in tape and printed forms (Astronomy and Astrophysics Supplement, 1985) as described below (Section X.E) and in Chapter IX.
Flux Density Uncertainties: RELUNC (4)
Each flux density measurement other than an upper limit has an associated uncertainty expressed as a 1 (X) value in units of l00 × (X). Uncertainties are discussed in Sections V.H.5. and VII.D.2.
Point Source Correlation: CC(4)
As described in Section V.C.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, 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). 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.
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 × 4.5' cross-scan (half-widths). As described in Sections V.H.3-4 and VII.H.1, values of SES1 greater than 1 should caution the
X-8
reader 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 × 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 µm 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 µm measurements three quantities have been established (Section V.H.4 and VII.H).
CIRR1 gives the number of 100 µm-only WSDB sources located within a 1/2 degree × 1/2 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 µm (see (Eq. V.H.2)). Values larger than 4-5 indicate the presence of considerable structure in the 100 µm emission on a 1/2 degree scale. A value of 0 indicates that no 1/2 degree data were available for the source in question.
CIRR3 is the total surface brightness of the sky surrounding the source in a 1/2 degree 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 = 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, 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.
B.2 The Printed Version of the Point Source Catalog
The printed version of the catalog is a strict subset of the information described in the preceding section. A number of fields have been abbreviated or deleted to make possible a single line entry for each source. The entries in the book are discussed below and shown as a figure in Fig. X.B. 1
Name: (NAME)
The full IRAS name is derived from the hours(HH), minutes(MM) and tenths of minutes(T) of right ascension and from the sign, degrees (DD) and minutes (MM) of declination. The right ascension and declination have been truncated.
Position:(RA(s), DEC("))
To conserve space, only the seconds of time for the right ascension and the arcseconds of declination are given. To reconstruct the source position one must also take the hours and minutes of the right ascension and the° and minutes of declination from the source name. Because the source name was obtained by truncating rather than rounding the positions, values of RA(s) and DEC(") as large as 60 are possible.
Galactic Coordinates
Galactic coordinates (X(II), b(II)) are given to a precision of 1 degree.
Positional Uncertainties (SMAJ,SMIN,PA)
Semi-major, semi-minor axes (") and the position angle (o) of the uncertainty ellipse are given as described in the previous section.
Number of Sightings (NH)
The number of hours-confirmed sightings.
Flux Densities
Non-color-corrected flux densities are given in Janskys in the four bands. A single character following the measurement denotes the flux quality of the observation (Section V.H.5). A blank denotes a high quality measurement, a':' denotes a moderate quality measurement and an 'L' denotes an upper limit. An 'S' indicates that all measurements in that band were saturated and that the value listed is the largest of all the saturated values.
Flux Density Uncertainties (FLUX/UNCS)
The relative uncertainties are given in each band for each high or moderate quality measurement according to the following convention (where the uncertainty was first rounded to two significant figures):
Symbol Uncertainty Range
A 0.00 (X) (X)fv/fv < 0.04
B 0.04 (X) (X)fv/fv < 0.08
C 0.08 (X) (X)fv/fv < 0.12
D 0.12 (X) (X)fv/fv < 0.16
E 0.16 (X) (X)fv/fv < 0.20
Correlation Coefficient (CORR/COEF)
As described in the previous section, the correlation coefficient of the source with the point source template is given in each band according to the convention A=100%, B=99%,...N=87%.
Variability (VAR)
The probability (0-99%) that a source detected at 12 and 25 µm is variable is truncated to a single digit 0-9. A blank indicates that the source did not qualify for variability testing.
The Confusion Block
Ten flags or values each consisting of a single digit are combined into a block to denote the presence of nearby sources of possible confusion. The flags are discussed in detail in the preceding section and in Section V.H. and include:
C1 = CIRR1 - the number of 100 µm only point sources.
C2 = CIRR2 - the ratio of 1/2 degree extended emission to the source flux.
CF = CONFUSE - hex-encoded flag indicating bands in which confirmation processor found confusion.
PH= PNEARH - number of nearby hours-confirmed sources.
PW = PNEARW - number of nearby weeks-confirmed sources.
S1-S4 = SES1 - number of nearby hours-confirmed small extended sources per band.
HD = hex-encoded flag indicating which bands, if any, were processed according to high source density rules (Section V.H.6).
Low-Resolution Spectra (LRS)
The presence of a low-resolution spectrum is indicated by this two-digit classification of the spectrum (Section IX.D).
Small Extended Source (S2)
The presence of one or more weeks-confirmed small extended sources is denoted by a hex-encoded flag denoting the bands in which a small extended source was found.
The Associations Block (NID,CAT,NAME,TYPE,RAD,MAG)
When an IRAS source is found to have at least one positional association with objects in other astronomical catalogs, one such association is printed. Six pieces of information are given as described in the previous section and in Section V.H.9. NID gives the total number of associations found in searching all catalogs. CAT is the number of the catalog (Tables V.H.1, X.B.4). The NAME and the TYPE (usually spectral or Hubble type) of the object are given. RAD is the distance from the IRAS source to the position of the associated object in arcsec. FIELD1, which is usually a magnitude, is given in the MAG field, when available, for all catalogs except 2 and 19, for which FIELD2 is given.
X-11
The association printed is chosen first by catalog within a catalog type (IDTYPE) as follows:
Catalogs in Order of Printing Priority
Printing Sequence
IDTYPE Type 1 2 3 4 5 6 7 8 9 l0 ll l2 l3 l4 l5-3l
1 Extragalactic 9 6 12 10 29 25 26 27 28 30 31 - - - -
2 stellar 13 4 15 2 1 7 16 17 18 19 24 - - - -
3 other 14 22 21 20 23 3 5 8 11 - - - - - -
4 multiple 13 9 14 1 2 3 4 5 6 7 8 10 11 12 15-31
If more than one association was found in the catalog chosen by the priority scheme, the closest associated source (smallest RAD) is printed.
B.3 The Working Survey Data Base
The most complete observational and data reduction history for point sources is contained within the Working Survey Data Base (WSDB). The WSDB is broken up into 20 files, one for each range of ecliptic longitudes called a Lune (see below). Each file is preceded by a header file containing a single 80-character ASCII record giving the date and version of the WSDB (Table X.A.1). Except as noted below, the entries are similar to those listed above for the catalog tape. Table X.B.3a lists the entries, their variable type and length. A second file, called the Ancillary file (Table X.B.3b) contains additional flags and derived quantities obtained during final product generation. Most of the information in the Ancillary file is the same as that in the catalog tape described in Section X.B. 1. Character variables are in ASCII format. All arithmetic quantities are in integer format with the high order byte first.
It is important to note that the WSDB and Ancillary files are in binary format with variable length, blocked records (due to the variable number of hours-confirmed sightings or associations). Extra information has been added to the WSDB and Ancillary file tapes to make it possible to read in these variable length records. Each physical block on the tape begins with a Block Control Word of length I*4. Its high order two bytes give the length of the physical block in bytes; this length includes the 4-byte length of the Block Control Word itself. In addition, each logical record within the physical block is preceded by a Segment Control Word of length I*4. Its high order two bytes give the length of the logical record in bytes; again, this length includes the 4-byte length of the Segment Control Word itself. The inclusion of this information should make it possible for computers that can work with Variable Block formats to easily read the tape. In no case does the information for a single source span two physical blocks.
The remainder of this section describes WSDB and ancillary file entries not discussed above.
X- 12
SDAS Lune Number: LUNE
In the data reduction the sky was divided into twenty "lunes" based on ecliptic coordinates. Lune 1 comprises that part of the sky with (X)>60°; Lune 2 comprises that sky with (X)<-60°. Lunes 3-20 comprise that part of the sky with |(X)|</-60 degree and ecliptic longitudes, (X) in 20 degree wide blocks. Lune 3 extends from 0 degree (X) < 20°, lune 4 from 20 degree < (X) < 40°. etc.
Ecliptic Bin Number: BIN
To aid the data reduction the entire sky was divided into some 40,000 1 sq. deg bins. The bin structure is quite simple in ecliptic coordinates (Fig. X.Ap1.1) and an algorithm for generating bin numbers is given in Appendix X. 1.
Ecliptic Coordinates: ELAT, ELONG
Ecliptic coordinates are given in units of 10-8 radians in the equinox 1950.
Scan Angle: SCAN
After weeks-confirmation SCAN gives the average scan angle of the focal plane with respect to the south-going local ecliptic meridian.
Positional Uncertainty: SIGY, LZ, SIGZ
As discussed in detail in Section V.D, the position refinement describes the source positional uncertainty in terms of 1 (X) in-scan and cross-scan gaussian uncertainties (SIGY and SIGZ) and a uniform uncertainty (of half-width LZ) whose size depends on the exact paths of the source across the focal plane.
Number of LRS Extractions: LRSX
Each time a source with a signal-to-noise ratio greater than 25 at either 12 or 25 µm transversed the focal plane, the data reduction software automatically triggered a request to extract a spectra from the low-resolution spectrometer data (Chapter IX). The threshold was purposefully set quite low so that sources with weak continuua but strong lines could be detected. Many sources with LRSX>0 will fail to have meaningful spectra and will thus have NLRS=0.
Known Source ID: KSID
The positions and predicted brightnesses of some 32,000 point sources including SAO stars, IRC objects and asteroids were incorporated into the data reduction software to provide a check on the positional and photometric accuracy of the IRAS sources. Table X.B.5 lists the range of KSID values assigned to sources of various types.
The following values are given for each hours-confirmed sighting:
Flux and Flux Uncertainty: FLUX(4),SIGF(4)
Flux and flux uncertainty measurements are given in units of 10-16W m-2 for each hours-confirmed sighting. Note that an instrumental flux, not the flux density, is given. In order to convert the instrumental flux to flux density, one must divide the instrumental flux by 13.48, 5.16, 2.58, 1.00 x 10 12 Hz at 12, 25, 60 and 100 µm respectively. The derivation of flux uncertainties and the averaging of the individual hour-confirmed fluxes to give the average value (see AVGFLUX, below) quoted in the catalog is discussed in Section V.H.5.
X- 13
Signal-to-Noise Ratio: TSNR(4)
If a source is detected (but not necessarily even seconds-confirmed) in a given band, then a value equal to ten times the maximum signal-to-noise ratio (SNR) observed on any detector in that band in the hours-confirmed sighting is retained. In relatively simple parts of the sky the noise estimator used to derive SNR gives reasonable values. In more complex regions near the Galactic plane (see Section V.C.2) the utility of SNR is very limited.
Correlation Coefficient: CORR
The maximum point source correlation coefficient (see Section V.C.4.) obtained during a hours-confirmed sighting is retained for each band. The values for each band, expressed as percentages up to a maximum of 100, are encoded into a single integer according to the following algorithm:
CORR = CC(1) x 224 + CC(2) x 216 + CC(3) x 28 + CC(4) (X.B.1)
Flux Status: FSTAT
In each band there is a hierarchy of measurement quality depending on how many times a given source is observed within a given hours-confirmed sighting. FSTAT plays a crucial role in determining whether a source is included in the catalog at all, whether a flux is of high, medium or low quality and how the flux averaging was performed (Section V.H.5). for the meaning of each FSTAT value refer to Section V.D.8.
The values of FSTAT for the four bands are compressed into a single integer according to the following algorithm:
FSTAT = FSTAT(1) x 2 12 + FSTAT(2) x 2 8 + (X.B.2)
FSTAT(3) x 24 + FSTAT(4)
Detector ID's: DETID
The identities of all detectors observing a given source on the sightings (up to a maximum of 3 sightings) comprising a given hours-confirmed observation are recorded in the array DETID(I,J). The four bands run from I=1 to 4 while the three sightings run from J=1 to 3.
Each value of DETID contains an integer that must be decoded according to the following algorithm to obtain the detectors observing the source:
DETID(I,J) = D1 x 2 10 + D2 x 2 5 + D3 (X.B.3)
where detector numbers, D1, D2 and D3, range from 1 to 16 within each band. Table X.B.6 lists the correspondence between detector number within a band to the true detector number. The order of detector number is significant as described in V.D.5. It should be emphasized that when three detectors are named in a sighting, indicating the presence of an edge detection, the weakest of the edge detections may not have played any part in the assignment of flux or position.
X- 14
Detector Name: DNAM, TNAM
Throughout the course of the data processing each hours-confirmed sighting is known by a combination of the first detector measuring the object (DNAM) and the time (in deci-UTCS since 1981, January 1, Oh UT) of that sighting (TNAM).
Confusion Status: CSTAT, PNEARH, PNEARW
At various stages in the reconstruction of a point source attempts are made to recognize (and remedy) the effects of confusion between nearby sources. The confusion status word CSTAT plays an important role in selecting sources to be treated by the "clean-up" processor (Section V.H.2) and in determining which sources to keep in regions of high source density (see Section V.H.6). for a detailed discussion of confusion processing see Section V.D.2. Values of CSTAT and brief descriptions of their meaning are given in Section V.D.8.
The values of CSTAT for each band are encoded into a single integer according to the following algorithm:
CSTAT = CSTAT(1) x 2 24 + CSTAT(2) x 2 16 (X.B.4)
+ STAT(3) x 2 8 + CSTAT(4)
The number of hours- and weeks-confirmed point sources within 6' x 4.5' (half-widths) of the quoted source, PNEARH and PNEARW, are encoded into a single byte:
PNEAR = PNEARW x 24 + PNEARN (X.B.5)
Cirrus Flags:. CIRRUS, CIRR1, CIRR2, CIRR3
The three flags denoting the presence of extended 100 µm emission ("cirrus") as discussed in Section V.H.4, are encoded in two bytes according to the algorithm:
CIRRUS = CIRR3 x 2 8 + CIRR1 x 2 4 + CIRR2 (X.B.6)
Values of CIRR2 = 0 and CIRR3 = 255 mean no data were available.
Small Extended Source Flags: SES1, SES2
The two small extended source flags for each band discussed in Section V.E. 1 are encoded into two integers according to the following algorithm:
SES1 = SES1(1) x 2 12 + SES1(2) x 2 8
+ SES1(3) x 2 4 + SES1(4) (X.B.7)
and
SES2 = SES2(1) x 2 12 + SES2(2) x 2 8
+ SES2(3) x 2 4 + SES2(4) (X.B.8)
X-15
Clean up Processors: CLEAN, BRIGHT, ACCEPT, HSDPROC, MISC
In creating the WSDB from the weeks-confirmed data, several processors were applied in order to fix various known problems (see Section V.H). These processors set various flags that allow the user to understand what processing occurred. The clean-up processor allowed the weeks-confirmation of various WSDB sources that did not previously have an opportunity to weeks-confirm for purely technical reasons or which were incorrectly split asunder during band merging. The flags set by that processor are described in Table X.B.7a., and include flags indicating saturated fluxes. Optical crosstalk from certain bright objects such as Saturn and IRC+10216 produced a few spurious sources. These were marked for deletion. The byte BRIGHT (Table X.B.7b) notes these cases and also contains flags denoting final acceptance (ACCEPT) or rejection of the source in each band. The flags from the High Source Density processor (HSDPROC, see Section V.H.6) are given in 2 bytes per band (Table X.B.7c). Miscellaneous flags are set in MISC (Table X.B.7d) and include the presence of flux discrepancies in each band, whether the in-scan positional uncertainties needed to be increased (Section VII.C) and whether the source was accepted in the catalog.
XII-16
Table X.B.3a. The Catalog Working Survey Data Base (WSDB)
Start
Byte Name Description Units Type
0* LUNE SDAS Lune number --- I*4
4 BIN Ecliptic Bin Number --- I*4
8 ELONG Ecliptic longitude 1950. 10-8 rad I*4
12 ELAT Ecliptic latitude 1950. 10-8 rad I*4
16 SCAN average scan angle with milli-rad I*2
respect to eclipitc
meridian
18 SIGY In-scan Gaussian u-rad I*2
position uncertainty
20 LZ Cross-scan Uniform u-rad I*2
position uncertainty
22 SIGZ Cross-scan Gaussian u-rad I*2
position uncertainty
24 LRSX Total number of LRS --- I*2
extraction requests
26 KSID Known Source ID --- I*2
28 NHCON Number of Hours- --- I*4
(<25) confirmed sightings
The following values repeat for each hours-confirmed sighting:
32 FLUX FLUX(I)=In-band power 10-16W m-2 4I*4
48 SIGF SIGF(I)=Uncertainty 10-16W m-2 4I*4
in FLUX(I)
64 TSNR TSNR(I)=10x(max SNR) --- 4I*2
72 CORR Maximum correlation --- I*4
coefficient (1 value
per band, Eq. X.B.1)
76 FSTAT Flux status --- I*2
word (1 value per
band, Eq.X.B.2)
88 DETID Detector ID Array --- 12I*2
(4,3) for 4 bands
(Eq.X.B.3)
102 LRSXNO Number of LRS extraction --- I*1
requests
103 DNAM detector part --- I*1
of source name
104 TNAM deci-UTCS part deci-sec I*4
of source name
108 CSTAT Confusion status flags --- I*4
(Eq.X.B.4)
112--- 191 repeats bytes 36-115
192--- 271 for subsequent hours
etc... confirmed sightings.
* See X.B.3 for discussion of block and segment control words
X-17
Table X.B.3b. Ancillary WSDB File
Start
Byte Name Description Units Type
0 1 PNEAR Nearby hours- and --- I*1
weeks-confirmed
neighbors
1 CLEAN Clean up Processor --- I*1
flags
2 SES1 Number of nearby --- I*2
unconfirmed SES
(4 bands encoded)
4 SES2 Number of nearby --- I*2
weeks-confirmed SES
(4 bands encoded)
6 CIRR1, Number of 100 µm --- I*2
CIRR2 only WSDB sources,
spatially filtered
100 µm emission.
CIRR3 value of 100 µm half- MJy sr-1
degree beam total
intensity
8 AVGFLUX AVGFLUX(I) Averaged flux 10-16W m-2 4I*4
(in-band power)
in band I.
24 AVGUNC AVGUNC(I) Uncertainty in 10-16W m-2 4I*4
averaged (in-band) flux
in band I.
40 HSDPROC HSDPROC(I). Flags set by --- 4I*2
the high source density
processor in band I
48 RA Right ascension 1950 10-5" I*4
52 DEC Declination 10-5" I*4
56 NAME source name --- A*12
68 NLRS Number of meaningful --- I*2
LRS spectra
70 LRSCHAR characterization of --- A*2
LRS spectra
72 BRIGHT Bright Source Clean up I*1
ACCEPT Flag for catalog sources
accepted in the catalog
73 VAR Percent likelihood of --- I*2
Variability
74 FQUAL FLUX Quality flags --- I*1
(one per band)
BIT 0-1, 12 µm
BIT 2-3, 25 µm, etc.
X- 18
Table X.B.3b. Ancillary WSDB File (Continued)
Start
Byte Name Description Units Type
75 MISC Miscellaneous Status --- I*1
bits, incl. DISC
ACCEPT,SIGY
See Table X.B.7d
76 LUNE SDAS Lune number --- I*4
80 BIN Ecliptic Bin Number --- I*4
84 ELONG Ecliptic longitude 10-8 rad I*4
88 ELAT Ecliptic Latitude 10-8 rad I*4
92 NID 2 Number of Associations I*2 (<25) to follow
94 IDTYPE Type of association --- I*2
96 CATNO Catalog Number --- I*2
98 SOURCE Source ID --- A*15
113 TYPE Source Type/Spectral Class --- A*5
118 RADIUS Position difference (") I*2
120 POS Position Angle ' E of N I*2
122 FIELD1 object field #1 --- I*2
124 FIELD2 object field #2 --- I*2
126 FIELD3 object field #3 --- I*2
128 continuation of association 3
-160 in blocks of 32 bytes
etc.
1 See X.B.3 for discussion of blcck and segment control words
2 If NID=0, one blank association field of 32 bytes is written.
3 CATNO,SOURCE,TYPE,RADIUS,POS,FIELD 1-3 are repeated in blocks of 32 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.
Table X.B.4 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 µm [decimag]
Field2 Magnitude at 11 µm [decimag]
Field3 Magnitude at 27 µm [decimag]
---------------------------------------------------------------------------------
4 2-µm 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 BT [decimag]
Field3 Do [arcsec]
-----------------------------------------------------------------------------
7 Stars with Type Blank
em. lines
Field1 V magnitude [decimag]
Field2 999
Field3 0
Table X.B.4 Meaning of the Source Association Fields (Continued)
Catalog Field and Meaning *
8 Equatorial Type Blank
IR Cat.
Field1 Flux density [10-16 W cm-2 µm-1] at 2.7 µm
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]
X-2l
Table X.B.4 Meaning of the Source Association Fields (Continued)
Catalog Field and Meaning *
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 [ K]
23 OSU Type Blank
Field1 999
Field2 999
Field3 Diameter [arcsec]
X-22
Table X.B.4 Meaning of the Source Association Fields (Continued)
Catalog Field and Meaning *
24 IRC Type C if 2.2 µm 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 time]
Field3 0
25 DDO Type Blank
Field1 999
Field 2 999
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
X-23
Table X.B.4. Meaning of the Source Association Fields (Continues)
Catalog Field and Meaning *
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
* In the printed version FIELD1 is listed if present except for catalogs 2 and 19, where FIELD2 is given.
VV Catalog Flags (Catalog 31)
FIELD1 Explanation
10 VV10 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 objest 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').
X-24
Table X.B.5 Known Source ID's
Range Source Type
1-465 Selected AFGL catalog sources
466-3157 Two Micron Sky Survey sources
without SAO counterparts
3158-26979 Selected SAO stars (mostly M
and K stars).
26980-27497 Selected objects for Low-Resolution
Spectrometer
>/-30000 Solar System Objects (asteroids,
comets and outer planets)
Table X.B.6 Detector Number
In Band True In Band True
Detector Detector Number Detector Detector Number
Number 12 µm 25 µm 60 µm 100 µm Number 12 µm 25 µm 60 um 100 µm
1 23 16 08 01 9 47 40 31 56
2 24 17 09 02 10 48 41 32 57
3 25 18 10 03 11 49 42 33 58
4 26 19 11 04 12 50 43 34 59
5 27 20 12 05 13 51 44 35 60
6 28 21 13 06 14 52 45 36 61
7 29 22 14 07 15 53 46 37 62
8 30 39 15 55 16 54 00 38 00
X-25
Table X.B.7a. CLEAN Bit Assignment
Bit # Meaning
0-3 Bits 0-3 denote a flux limit derived
solely from saturated detections.
Bit 0=12 µm, Bit 1=25 µm.
4 Source failed to weeks-confirm with
another WSDB source in the mini-survey
region.
5 Source resulted from weeks-confirming
at least two WSDB sources in the mini-survey
region.
6 Source failed to weeks-confirm with
another WSDB entry observed within
36 hours.
7 Source resulted from weeks-confirmation
of two separate WSDB sources observed
within 36 hours of each other.
Table X.B.7b. BRIGHT/ACCEPT Bit Assignment
Bit # Meaning
0 false source generated by nearby bright
source
l-4 Source satisfies single
band acceptance criteria
BIT 1 = 12 µm, Bit 2=25 µm, etc.
5-7 Source satisfies adjacent
band acceptance criteria
BIT 5 = 12 and 25 µm
BIT 6 = 25 and 60 µm
BIT 7 = 60 and 100 µm
----J
X-26
Table X.B.7c. 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
X-27
Table X.B.7d. MISC Bit Assignment
Bit # Meaning
0-3 Discrepant Flux found in band.
BIT 0, 12 µm,
BIT 1, 25 µm, etc.
4,5 SPARE
6 (X) fix (Section VII.C)
7 Source accepted in catalog