IRAS Explanatory Supplement
X. The Formats of the IRAS Catalogs and Atlases
Appendix X.1 Regions of High Source Density
As discussed in Section V.H.6, regions with more sources per sq. deg than the confusion limit in a given band were processed according to more stringent rules to insure the reliability of the data presented in the catalog. The regions so processed were selected on a band by band basis depending on the number of sources with high or moderate quality fluxes located within a 1 sq. deg bin in ecliptic coordinates.
Users of the catalog who want to know the identity of those regions may use a machine readable file that lists the bin number (see below), a flag called HSD which indicates which bands in that bin were processed according to high source density rules, the ecliptic coordinates of the center of the bin, and its length in ecliptic longitude. All bins have a height of 1 degree in ecliptic latitude. The file consists of 80-character ASCII records with 256 records per physical block. The information for two bins fits within a single 80-character logical record. This file is preceded on the tape by a short file which contains a single 80-character ASCII record which lists the date and version number of the information.
The flag HSD is hex-encoded by band, as described in Table X.B.2. In this notation each band corresponds to one of the four bits of a hex digit. 12 µm corresponds to bit 0 (Least Significant Bit) and 100 µm to bit 3, etc. If a band went through high source density processing in that band, then the appropriate bit in the hex digit was set. Thus, if high source density rules were invoked at 25, 60 and 100 µm, HSD would have the value 1110 (binary) = E (hex).
Ecliptic bins start at the ecliptic north pole and step around the sky in bands of constant ecliptic latitude, stepping 1 degree southward after completing each band. The length of the bin, in ecliptic longitude, was adjusted for the cosine of the ecliptic latitude to maintain an approximately constant area. FORTRAN programs are given below to convert from bin number to ecliptic coordinates and vice versa. There is a known bug in the computation of bins at ecliptic latitude 60°, causing bin 2842 to be skipped. The following program, while incorrect in this way, will give results consistent with the bin numbers used in the data processing. To avoid problems with roundoff errors within a few arcseconds of bin boundaries, all arithmetic should be calculated in double precision.
FORTRAN Program to Convert between Ecliptic Position and Bin Number
C
C CONVERT AN ECLIPTIC POSITION TO BIN NUMBER.
SUBROUTINE P2BIN(LAM,BET,BIN)
IMPLICIT REAL*8 A-H, P-Z
REAL*8 LAM,BET,LSIZE,R2D/57.2957795/
INTEGER*4 BIN,I,J,N,MAXBIN(182)
COMMON /LATBND/MAXBIN
C
I = 90. - BET*R2D + 2.5
N = MAXBIN(I) - MAXBIN(I-l)
LSIZE = 360./FLOAT(N)
J = LAM*R2D/LSIZE + 1
BIN = MAXBIN(I-l) + J
RETURN
END
C
C CONVERT A BIN NUMBER TO A CENTER POSITION AND LONGITUDE LENGTH.
SUBROUTINE BIN2P(BIN,CLON,CLAT,LWIDTH)
IMPLICIT REAL*8 A-H,P-Z
INTEGER*4 BIN,I,J,MAXBIN(182),FIRST
REAL*8 CLON,CLAT,LWIDTH,R2D/57.2957795/,NBINS
COMMON/LATBND/MAXBIN
C
DO 100 I=1,182
IF(MAXBIN(I).GE.BIN)GOTO 150
100 CONTINUE
150I=I-1
FIRST = MAXBIN(I) +1
NBINS = MAXBIN(I+1) - FIRST + 1
LWIDTH = 360./NBINS
J = BIN - FIRST
CLON = DFLOAT(J)*LWIDTH + LWIDTH/2.
CLAT = 90. -DFLOAT(I-1)
LWIDTH = LWIDTH/R2D
CLON = CLON/R2D
CLAT = CLAT/R2D
RETURN
END
C
C DATA SUBPROGRAM.
BLOCK DATA
INTEGER*4 MAXBIN(182)
DATA MAXXBIN
* /0,1,7,19,37,62,93,130,173,223,279,341,409,483,563,
* 650,743,842,947,1058,1175,1298,1427,1561,1701,1847,l999,
* 2156,2319,2488,2662,2841,3026,3216,3412,3613,3819,4030,
* 4246,4467,4693,4924,5160,5400,5645,5895,6149,6407,6670,
* 6937,7208,7483,7762,8045,8332,8623,8917,9215,9516,9821,
* 10129,10440,10754,11071,11391,11714,12040,12368,12699,
* 13032, 13368,13706,14046,14388,14732,15078,15425,15774,
* 16124,16476,16829,17183,17538,17894,18251,18609,18967,
* 19326,19685,20044,20403,20763,21122,21481,21840,22199,
* 22557,22915,23272,23628,23983,24337,24690,25042,25392,
* 25741,26088,26434,26778,27120,27460,27798,28134,28467,
* 28798,29126,29452,29775,30095,30412,30726,31037,31345,
* 31650,31951,32249,32543,32834,33121,33404,33683,33958,
* 34229,34496,34759,35017,35271,35521,35766,36006,36242,
* 36473,36699,36920,37136,37347,37553,37754,37950,38140,
* 38325,38505,38679,38848,39011,39168,39320,39466,39606,
* 39740,39869,39992,40109,40220,40325,40424,40517,40604,
* 40684,40758,40826,40888,40944,40994,41037,41074,41105,
* 41130,41148,41160,41166,41167/
COMMON/LATBND/MAXBIN
END
| Byte | Name | Description | Units | Format |
|---|---|---|---|---|
| 00 | BINNUM | SDAS Bin Number | --- | 16 |
| 06 | HSD | Bands processed for high source density, hex encoded by band. | --- | A2 |
| 08 | LAMBDA | Ecliptic longitude of bin center | deg | 10.5 |
| 18 | BETA | Ecliptic latitude of bin center | deg | 10.5 |
| 28 | LENGTH | Length of bin in ecliptic longitude | deg | 10.5 |
| 38 | SPARE | 2 spare bytes | --- | 2A1 |
| 40-79 | bytes 00-39 are repeated for next bin | |||
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