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SRoll FITS file format description

 

 

Multibolometer polarized maps (100-353 GHz)

SRoll multibolometer polarized maps FITS files are formatted in the same way as in the Planck Legacy Archive (PLA) HFI2018 release:

http://pla.esac.esa.int/pla/#maps

as documented in the PLA explanatory supplement:

https://wiki.cosmos.esa.int/planck-legacy-archive/index.php/Frequency_maps

 

More explicitly, each FITS file contains a first (primary) header without data, and an extension with a header and a 10 column table. Each column is a HEALPix map at Nside=2048, in GALACTIC coordinates and NESTED ordering. The first three columns are the I_STOKES, Q_STOKES and U_STOKES components in single precision floating point, the fourth column is the HIT count map in 32bit integer, and the last six columns are the upper triangular part of the 3x3 symmetric covariance matrix, II, IQ, IU, QQ, QU and UU respectively, in single precision floating point data type.

 

The output of the fitsheader command (http://docs.astropy.org/en/stable/io/fits/usage/scripts.html) on one of these files is given here for further documentation:

 

$ fitsheader SRoll20_SkyMap_100psb_full.fits
# HDU 0 in SRoll20_SkyMap_100psb_full.fits:
SIMPLE  =                    T / conforms to FITS standard
BITPIX  =                    8 / array data type
NAXIS   =                    0 / number of array dimensions
EXTEND  =                    T

# HDU 1 in SRoll20_SkyMap_100psb_full.fits:
XTENSION= 'BINTABLE'           / binary table extension
BITPIX  =                    8 / array data type
NAXIS   =                    2 / number of array dimensions
NAXIS1  =                   40 / length of dimension 1
NAXIS2  =             50331648 / length of dimension 2
PCOUNT  =                    0 / number of group parameters
GCOUNT  =                    1 / number of groups
TFIELDS =                   10 / number of table fields
TTYPE1  = 'I_STOKES'
TFORM1  = 'E       '
TUNIT1  = 'Kcmb    '
TTYPE2  = 'Q_STOKES'
TFORM2  = 'E       '
TUNIT2  = 'Kcmb    '
TTYPE3  = 'U_STOKES'
TFORM3  = 'E       '
TUNIT3  = 'Kcmb    '
TTYPE4  = 'HITS    '
TFORM4  = 'J       '
TUNIT4  = ''
TTYPE5  = 'II_COV  '
TFORM5  = 'E       '
TUNIT5  = 'Kcmb^2  '
TTYPE6  = 'IQ_COV  '
TFORM6  = 'E       '
TUNIT6  = 'Kcmb^2  '
TTYPE7  = 'IU_COV  '
TFORM7  = 'E       '
TUNIT7  = 'Kcmb^2  '
TTYPE8  = 'QQ_COV  '
TFORM8  = 'E       '
TUNIT8  = 'Kcmb^2  '
TTYPE9  = 'QU_COV  '
TFORM9  = 'E       '
TUNIT9  = 'Kcmb^2  '
TTYPE10 = 'UU_COV  '
TFORM10 = 'E       '
TUNIT10 = 'Kcmb^2  '
PIXTYPE = 'HEALPIX '           / HEALPIX pixelisation
ORDERING= 'NESTED  '           / Pixel ordering scheme, either RING or NESTED
COORDSYS= 'GALACTIC'           / Ecliptic, Galactic or Celestial (equatorial)
EXTNAME = 'FREQ-MAP'           / Extension name
NSIDE   =                 2048 / Resolution parameter of HEALPIX
FIRSTPIX=                    0 / First pixel # (0 based)
LASTPIX =             50331647 / Last pixel # (0 based)
INDXSCHM= 'IMPLICIT'           / Indexing: IMPLICIT or EXPLICIT
OBJECT  = 'FULLSKY '           / Sky coverage, either FULLSKY or PARTIAL
BAD_DATA=          -1.6375E+30 / HEALPIX bad pixel value
DATE    = '2018-12-27'         / Creation date (YYYY-MM-DD)
POLCCONV= 'COSMO   '           / Polarization convention
FILENAME= 'SRoll20_SkyMap_100psb_full.fits' / FITS filename
FREQ    = '100     '           / reference frequency
PROCVER = 'SRoll20 '           / Product version
UNITFREQ= 'GHz     '           / frequency units
BNDCTR  = '100     '           / band center, same as FREQ
RESTFRQ =               100.89 / effective frequency
BNDWID  = '33      '           / effective bandwidth (approximate)
PROCDSET= '100psb  '           / processed detector set
PROCRSET= 'full    '           / processed ring set
PLOTDSET= '100psb  '           / plotted detector set
PLOTRSET= 'full    '           / plotted ring set

 

 

Multibolometer unpolarized maps (545-857 GHz)

545 GHz and 857 GHz HFI channels don't contain polarization sensitive bolometers and their frequency maps are therfore intensity only. They nevertheless follow the same formatting as the Planck 2018 FITS files, the only difference being the content of the columns in the FITS file extension.

The multibolometer unpolarized maps FITS file extension columns are:

 

 

Monobolometer maps for polarized channels (100-353 GHz)

They also use the same formatting as the Planck 2018 FITS files, with the following columns:

 

 

Monobolometer maps for unpolarized channels (545-857 GHz)

They still use the same formatting as the Planck 2018 FITS files, with the following columns: