Astrometric Calibration

File Format: FITS binary table

Name: asTrans-rrrrrr.fit for those produced by ASTROM, scTrans-rrrrrr-c.fit for those produced by SSC, where rrrrrr is the imaging run number and c is the camera column.

Produced by: astrom, ssc

Used by: ps, frames

Size: 2880 + Nccds * (2880 + (Nfields * 156, rounded up to an even multiple of 2880)) bytes. Total of 4,841.28 Kb for the photometric file with all 30 photometric CCDs for a run with 1000 fields.

Archived? Yes

Description

Astrometric transformations for every field in a single imaging run. It transforms frame (row,col) coordinates to great circle (mu,nu) coordinates for a given inclination.
  r-i < riCut:

      rowm = row + dRow0 + dRow1*col + dRow2*(col^2) + dRow3*(col^3) + csRow*(color)
      colm = col + dCol0 + dCol1*col + dCol2*(col^2) + dCol3*(col^3) + csCol*(color)

  r-i >= riCut

      rowm = row + dRow0 + dRow1*col + dRow2*(col^2) + dRow3*(col^3) + ccRow
      colm = col + dCol0 + dCol1*col + dCol2*(col^2) + dCol3*(col^3) + ccCol

  mu = a + b * rowm + c * colm
  nu = d + e * rowm + f * colm
The color to use is u-g for u, g-r gor g, and r-i for r, i, z and the astrometric filters. The order of the extension HDUs is determined by the PDU keywords CCDARRAY, which is set to "astro" if this file is for the astrometric chips or "photo" if this file is for the photometric chips, CAMCOLS, which contains a white-space separated list of the columns in the imaging camera processed, and FILTERS, which contains a white-space separated list of the filters/camera-rows processed. There is one HDU per CCD processed, in order as listed in CAMCOLS and FILTERS, with FILTERS being the most rapidly varying index if CCDARRAY is set to "photo", and CAMCOLS being the most rapidly varying index if CCDARRAY is set to "astro". For example, if the PDU contains the keywords:
CCDARRAY= 'photo   '           / CCDs
CAMCOLS = '1 2 3   '           / Columns in the imaging camera processed.
FILTERS = 'r i     '           / Filters (rows in the imaging camera) processed.
then the HDUs in the file are ordered as follows:
PDU
HDU camCol=1, filter=r
HDU camCol=1, filter=i
HDU camCol=2, filter=r
HDU camCol=2, filter=i
HDU camCol=3, filter=r
HDU camCol=4, filter=i
The errors, muErr and nuErr, are the errors in the transformation (that is, the rms systematic errors) in great circle longitude and latitude, respectively. For the r' chips, this is the error in the absolute astrometry (r' coordinates to sky). For the u', g', i', and z' chips, this is the error in the relative astrometry (u', g', i', or z' to r'). For example, to transform g' pixel coordinates to r' pixel coordinates, one applies the g' TRANS structure to the g' coordinates, and then the inverse r' TRANS structure to the intermediate sky coordinates. The total error in this transformation is just the errors listed in the g' TRANS structure. Those errors are in arcsec; to convert to errors in the transformed r' coordinates just divide by the pixel scale for the r' CCD.

Primary Header

TRANS files produced by SSC have the "SSC_ID" keyword, identifying the SSC pipeline run which produced the file, but don't have the "ASTRO_ID", "SSCXX_ID", or "PSXX_ID" keywords. TRANS files produced by ASTROM have the "ASTRO_ID" keyword, identifying the ASTROM pipeline run which produced the file, but don't have the "SSC_ID" keyword. For ASTROM produced TRANS files, if the input FANG files came from SSC then there is an "SSCXX_ID" keyword for each camera column processed, identifying the SSC pipeline run which produced those FANG files, whereas if the FANG files came from PS then there is a "PSXX_ID" keyword for each column.

[an error occurred while processing this directive]

SIMPLE  =                    T
BITPIX  =                    8
NAXIS   =                    0
EXTEND  =                    T
VERSION = 'XXX     '           / Version of software used.
ASTRO_ID= 'XXX     '           / ASTROM pipe run id (ASTROM TRANS files only)
SSC_ID  = 'XXX     '           / SSC pipeline run id (SSC TRANS files only)
INCL    =            XXX.XXXXX / Great circle inclination wrt cel. eq. (degrees)
NODE    =            XXX.XXXXX / RA of great circle's asending node. (degrees)
EQUINOX =              XXXX.XX / Equinox of great circle coordinates. (years)
FIELD0  =                  XXX / First field reduced.
NFIELDS =                  XXX / Number of fields reduced.
KO_VER  = 'XXX     '           / Version of known object catalog used.
RUN     =                  XXX / Imaging run number.
[an error occurred while processing this directive]
CCDARRAY= 'photo   '           / CCD array (photo or astro)
CAMCOLS = '1 2 3 4 5 6'        / Columns in the imaging camera processed.
FILTERS = 'r i u z g'          / Filters (rows in the imaging camera) processed.
COMMENT  The following keywords are for ASTROM TRANS files only:
SSC01_ID= 'XXX     '           / SSC pipeline run identifier for column 1.
SSC02_ID= 'XXX     '           / SSC pipeline run identifier for column 2.
SSC03_ID= 'XXX     '           / SSC pipeline run identifier for column 3.
SSC04_ID= 'XXX     '           / SSC pipeline run identifier for column 4.
SSC05_ID= 'XXX     '           / SSC pipeline run identifier for column 5.
SSC06_ID= 'XXX     '           / SSC pipeline run identifier for column 6.
SSC07_ID= 'XXX     '           / SSC pipeline run identifier for column 7.
SSC08_ID= 'XXX     '           / SSC pipeline run identifier for column 8.
SSC09_ID= 'XXX     '           / SSC pipeline run identifier for column 9.
SSC10_ID= 'XXX     '           / SSC pipeline run identifier for column 10.
SSC11_ID= 'XXX     '           / SSC pipeline run identifier for column 11.
PS01_ID = 'XXX     '           / PS pipeline run identifier for column 1.
PS02_ID = 'XXX     '           / PS pipeline run identifier for column 2.
PS03_ID = 'XXX     '           / PS pipeline run identifier for column 3.
PS04_ID = 'XXX     '           / PS pipeline run identifier for column 4.
PS05_ID = 'XXX     '           / PS pipeline run identifier for column 5.
PS06_ID = 'XXX     '           / PS pipeline run identifier for column 6.
COMMENT mu nu are defined as:
COMMENT   r'-i' < riCut:
COMMENT       rowm = row+dRow0+dRow1*col+dRow2*(col^2)+dRow3*(col^3)+csRow*c
COMMENT       colm = col+dCol0+dCol1*col+dCol2*(col^2)+dCol3*(col^3)+csCol*c
COMMENT   r'-i' >= riCut
COMMENT       rowm = row+dRow0+dRow1*col+dRow2*(col^2)+dRow3*(col^3)+ccRow
COMMENT       colm = col+dCol0+dCol1*col+dCol2*(col^2)+dCol3*(col^3)+ccCol
COMMENT   mu = a + b * rowm + c * colm
COMMENT   nu = d + e * rowm + f * colm
END

Table Header

There is one HDU of this type per CCD. Note: the "field" field is the same value as the "id" attribute in TRANS structures.

[an error occurred while processing this directive]
XTENSION= 'BINTABLE'          
BITPIX  =                    8
NAXIS   =                    2
NAXIS1  =                  180
NAXIS2  =                  XXX
PCOUNT  =                    0
GCOUNT  =                    1
TFIELDS =                   24
FILTER  = 'XXX     '           / Filter (u, g, r, i, or z).
CAMCOL  =                  XXX / Column in the imaging camera.
[an error occurred while processing this directive]
CAMROW  =                  XXX / Row in the imaging camera.
[an error occurred while processing this directive]
TFORM1  = '1J      '          
TTYPE1  = 'field   '           / Field sequence number within the run.
TFORM2  = '1D      '          
TTYPE2  = 'a       '           / A.
TFORM3  = '1D      '          
TTYPE3  = 'b       '           / B.
TFORM4  = '1D      '          
TTYPE4  = 'c       '           / C.
TFORM5  = '1D      '          
TTYPE5  = 'd       '           / D.
TFORM6  = '1D      '          
TTYPE6  = 'e       '           / E.
TFORM7  = '1D      '          
TTYPE7  = 'f       '           / F.
TFORM8  = '1D      '          
TTYPE8  = 'dRow0   '           / Zero-order row distortion coefficient.
TFORM9  = '1D      '          
TTYPE9  = 'dRow1   '           / First-order row distortion coefficient.
TFORM10 = '1D      '          
TTYPE10 = 'dRow2   '           / Second-order row distortion coefficient.
TFORM11 = '1D      '          
TTYPE11 = 'dRow3   '           / Third-order row distortion coefficient.
TFORM12 = '1D      '          
TTYPE12 = 'dCol0   '           / Zero-order column distortion coefficient.
TFORM13 = '1D      '          
TTYPE13 = 'dCol1   '           / First-order column distortion coefficient.
TFORM14 = '1D      '          
TTYPE14 = 'dCol2   '           / Second-order column distortion coefficient.
TFORM15 = '1D      '          
TTYPE15 = 'dCol3   '           / Third-order column distortion coefficient.
TFORM16 = '1D      '          
TTYPE16 = 'csRow   '           / Slope in row DCR correction for blue objects.
TFORM17 = '1D      '          
TTYPE17 = 'csCol   '           / Slope in column DCR correction for blue objects
TFORM18 = '1D      '          
TTYPE18 = 'ccRow   '           / Constant row DCR correction for red objects.
TFORM19 = '1D      '          
TTYPE19 = 'ccCol   '           / Constant column DCR correction for red objects.
TFORM20 = '1D      '          
TTYPE20 = 'riCut   '           / r'-i' cutoff between blue and red objects.
TFORM21 = '1D      '          
TTYPE21 = 'mjd     '           / MJD(TAI) when row 0 was read.
TUNIT21 = 'MJD     '          
TFORM22 = '1D      '          
TTYPE22 = 'airmass '           / Airmass for star at frame center (mid exposure)
TFORM23 = '1E      '
TTYPE23 = 'muErr   '           / Error in transformation in mu
TUNIT23 = 'arcsec  '
TFORM24 = '1E      '
TTYPE24 = 'nuErr   '           / Error in transformation in nu
TUNIT24 = 'arcsec  '
[an error occurred while processing this directive]
END