IRAS Low-Resolution All-Sky Maps FormatTable 1 shows the header of the ALLSKY_GC_H1B4 image, the map centered at l = 0°, b = 0°, for HCON 1 and the 100 micron band.
Table 1. Sample FITS header
SIMPLE = T / STANDARD FITS FORMAT
BITPIX = 32 / 4-BYTE TWOS-COMPL INTEGERS
NAXIS = 3 / NUMBER OF AXES
NAXIS1 = 649 / # SAMPLES PER LINE (FASTEST VARY NDEX)
NAXIS2 = 325 / # LINES OF DATA IN IMAGE FILE
NAXIS3 = 1 / # WAVELENGTHS
BSCALE = 2.499999E+05 / TRUE=TAPE*BSCALE+BZERO
BZERO = 0.0 /
BUNIT = 'JY/SR ' / INTENSITY
BLANK = -2000000000 / TAPE VALUE FOR EMPTY PIXEL
CRVAL1 = 0.0 / GALACTIC LONGITUDE AT ORIGIN (DEGREES)
CRPIX1 = 325. / SAMPLE AXIS ORIGIN (PIXEL)
CTYPE1 = 'LON--ATF' / DECREASES IN VALUE AS SAMPLE INDEX
COMMENT INCREASES (AITOFF PROJECTION)
CDELT1 = -0.5 / COORD VALUE INCREMENT DEG/PIXEL
COMMENT AT ORIGIN ON SAMPLE AXIS
CRVAL2 = 0.0 / GALACTIC LATITUDE AT ORIGIN (DEGREES)
CRPIX2 = 163. / LINE AXIS ORIGIN (PIXEL)
CTYPE2 = 'LAT--ATF' / DECREASES IN VALUE AS LINE INDEX
COMMENT INCREASES (AITOFF PROJECTION)
CDELT2 = -0.5 / COORD VALUE INCREMENT DEG/PIXEL
COMMENT AT ORIGIN ON LINE AXIS
CRVAL3 = 1.0E-04 / WAVELENGTH IN METERS
CRPIX3 = 1.
CTYPE3 = 'LAMBDA '
CDELT3 = 0.
DATAMAX = 8.191746E+09 / JY/SR (TRUE VALUE)
DATAMIN = 5.499999E+06 / JY/SR (TRUE VALUE)
EPOCH = 1950. / EME50
DATE-MAP= '01/11/84' / MAP RELEASE DATE (DD/MM/YY)
DATE = '12/05/86' / DATE THIS TAPE WRITTEN (DD/MM/YY)
ORIGIN = 'JPL-IRAS' / INSTITUTION
TELESCOP= 'IRAS '
INSTRUME= 'ALL SKY ' / IRAS LOW RES ALL-SKY
OBJECT = 'CENTER 1' / ALL-SKY GALACTIC CENTER / HCON
PROJTYPE= 'AITOFF ' / PROJECTION TYPE
COMMENT MINSOP = 29; MAXSOP = 425
COMMENT
COMMENT PROJECTION FORMULAE:
COMMENT FORWARD FORMULA; XLON0 IS THE CENTER LONGITUDE OF THE
COMMENT MAP. ARC-SINE AND ARC-COSINE FUNCTIONS ARE REQUIRED.
COMMENT R2D = 45. / ATAN(1.)
COMMENT PIX = 2.
COMMENT RHO = ACOS( COS(XLAT) * COS((XLON-XLON0)/2.) )
COMMENT THETA = ASIN( COS(XLAT) * SIN((XLON-XLON0)/2.) / SIN(RHO) )
COMMENT F = 2. * PIX * R2D * SIN(RHO/2.)
COMMENT SAMPLE = -2. * F * SIN(THETA)
COMMENT XLINE = -F * COS(THETA)
COMMENT IF(XLAT .LT. 0.) XLINE = -XLINE
COMMENT
COMMENT REVERSE FORMULA; XLON0 IS THE CENTER LONGITUDE OF THE MAP.
COMMENT ARC-SINE AND ARC-COSINE FUNCTIONS NEEDED.
COMMENT R2D = 45. / ATAN(1.)
COMMENT PIX = 2.
COMMENT Y = -XLINE / (PIX * 2. * R2D)
COMMENT X = -SAMPLE / (PIX * 2. * R2D)
COMMENT A = SQRT(4.-X*X-4.*Y*Y)
COMMENT XLAT = R2D * ASIN(A*Y)
COMMENT XLON = XLON0 + 2. * R2D * ASIN(A*X/(2.*COS(XLAT)))
COMMENT
COMMENT REFERENCES:
COMMENT IRAS SDAS SOFTWARE INTERFACE SPECIFICATION(SIS) #623-94/NO. SF05
COMMENT ASTRON. ASTROPHYS. SUPPL. SER. 44,(1981) 363-370 (RE:FITS)
COMMENT RECONCILIATION OF FITS PARMS W/ SIS SF05 PARMS:
COMMENT NAXIS1 = (ES - SS + 1); NAXIS2 = (EL - SL + 1);
COMMENT CRPIX1 = (1 - SS); CRPIX2 = (1 - SL)
END
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