Deep Lens Survey: FITS Headers

The headers are so heavily commented as to be self-explanatory, so we simply give an example below. There are only a few points to add:
  • This applies to the second release; headers in the first release were much more primitive.
  • The second release originally did not have these headers; they were missing important things and had a lot of extraneous, confusing parts. As of Dec. 9, 2002, all (second-release) headers have been updated to look like this. The data have not changed at all.
  • We appreciate any feedback on the header contents, especially in terms of making them compatible with other surveys.
  • We have not commented the CTYPE/CRVAL/CRPIX/CD keywords because they are automatically read by software packages such as ds9. If you want to learn more about World Coordinate Systems, start with the WCSTools home page for more info. 


SIMPLE  =                    T / Fits standard
BITPIX  =                   16 / Bits per pixel
NAXIS   =                    2 / Number of axes
NAXIS1  =                 8192 / Axis length
NAXIS2  =                 8192 / Axis length
EQUINOX =                2000. / Equinox of coordinate system
CTYPE1  = 'RA---TAN'
CTYPE2  = 'DEC--TAN'
CRVAL1  = 1.40654583333300E+02
CRVAL2  = 3.06666666667000E+01
CRPIX1  = 4.09600000000000E+03
CRPIX2  = 4.09600000000000E+03
CD1_1   = 0.00000000000000E+00
CD1_2   = -7.13889000000000E-05
CD2_1   = -7.13889000000000E-05
CD2_2   = 0.00000000000000E+00
SURVEY  = 'DLS     '           / Deep Lens Survey
COMMENT   The Deep Lens Survey (DLS) is a deep BVRz' survey of 7 2x2-degree
COMMENT   fields. Data have been processed through flatfielding with standard
COMMENT   IRAF (mscred) tasks, then registered and combined (mean with 3-sigma
COMMENT   clip) with custom software. See http://dls.bell-labs.com and
COMMENT   astro-ph/0210118 for details. All processing was done with floating 
COMMENT   point computation, then truncated to integer to minimize storage
COMMENT   space and transport time. No significant bits have been lost, as the
COMMENT   sky noise is everywhere significantly greater than unity. Astrometry
COMMENT   is good to better than 0.3 arcsec. MAGZEROs are good to about 0.1.
OBJECT  = 'F2p11   '
COMMENT   DLS naming convention: fields are designated F1-F7. The coordinates
COMMENT   of each field center may be obtained at http://dls.bell-labs.com.
COMMENT   Each field is split into a 3x3 array of 40-arcmin subfields
COMMENT   designated p11 through p33, p11 being NE of center, p12 N of center,
COMMENT   p13 NW, p21 E, p22 central, etc, through p33 SW of center.
FILTER  = 'R       '
COMMENT   Filter curves are available at:
COMMENT   KPNO: http://www.noao.edu/kpno/mosaic/filters/filters.html
COMMENT   CTIO: http://www.ctio.noao.edu/instruments/filters/filters_66.html
RELEASE = '2       '           / DLS Sequential Release Number
COMMENT   DLS Releases correspond to release dates as follows:
COMMENT   1: September 2001
COMMENT   2: September 2003
COMMENT   Each release involves only the areas which reached full depth in the
COMMENT   preceding year. All data within a release were processed uniformly,
COMMENT   but there are differences from release to release. After all data are
COMMENT   acquired, there will be a final, uniformly processed release. 
DLSID   = 'F2p11R2 '           / concatenation of OBJECT, FILTER, and RELEASE
TELESCOP= 'kp4m    '
OBSERVAT= 'KPNO    '
DETECTOR= 'Mosaic  '
PROPID  = '0018    '           / NOAO tracking number
EFFGAIN =                  60. / effective gain for 20 exposures
MAGZERO =                31.99
COMMENT   Magnitude zero points were determined from observations of Landolt
COMMENT   (AJ 104, 340, 1992) fields. For BVRI (F1p22 has I data in addition to
COMMENT   BVRz'), the zeropoint is in the Vega system. For z, we used the
COMMENT   subset of Landolt stars calibrated by the SDSS and the resulting
COMMENT   zeropoint is in the AB system used by the SDSS.
DATEOBS1= '1999-11-11T09:56:54.0' / date of first exposure
DATEOBS2= '2001-12-18T12:53:54.0' / date of last exposure
EXPTIME =               12000. / total exposure time, seconds
SKYNOISE=                  1.9 / rms, ADU
FWHM    =                 1.08 / arcsec
DEPTH   =             27.78901 / 5-sigma depth according to NOAO formula:
COMMENT   DEPTH = MAGZERO - 2.5log(1.2*nsigma*FWHM*SKYNOISE//PIXSCALE)
COMMENT   The following are derived from the WCS and are provided for
COMMENT   convenience only. The WCS is definitive.
PIXSCALE=                0.257 / arcsec per pix   
RA      = '09:22:37.10'
DEC     = '+30:40:00.00'
CHECKSUM= 'BaMFEaM9BaMCBaM9'   / HDU checksum updated 2002-12-09T19:07:07
DATASUM = '1877981949'         / data unit checksum updated 2002-12-09T19:07:07