ISOCAM Interactive Analysis User's Manual Version 5.0 - ISO - ESA

8.3. CALCULATE STOKE PARAMETERS 55
8.2.5 Flat-field correction
For the flat-field correction we must use special flat-fields. These are distributed with CIA as
IDL savesets and must be restored manually:
CIA> help, pds_polar1.pfov, pds_polar1.fltrwhl
FLOAT = 3.00000
STRING = ’LW2’
CIA> restore, file=’$cia_vers/data/cds/fl_lw2_p1_6.xdr’
Now use corr flat to do the flat correction, supplying the restored flat-field image:
CIA> corr_flat, pds_polar1, inflat=flat
8.2.6 Photometry
Before performing astrometry we should convert the pixel values to mJy in both the EXPO-
SUREs and the MOSAIC image:
CIA> conv_flux, pds_polar1, /image
CIA> raster_scan, pds_polar1
Now perform photometry on each reduced EXPOSURE – use xphot or any other program
of your choice.
CIA> xphot, pds_polar1.image[*,*,0]
You can also perform photometry on the raster MOSAIC. The results should be consistent
with flux measurements on the EXPOSUREs.
8.3 Calculate Stoke parameters
At this stage you need to have a calibrated PDS for each of the polarizors and photometric
measurements for the source as seen through each polarizor. To calculate the Stokes parameters
we first need to calculate the polar weights with get polar weights:
CIA> fltrwhli = convert_wheel_back(’FLTRWHL’+pds_polar1.channel, $
CIA> pds_polar1.fltrwhl)
CIA> get_polar_weight, fltrwhli, pds_polar1.pfov, w1, w2, w3, dw1, dw2, dw3
not exact matching for pfov, I take the first complete set of data for
polarizors for the pfov
360
CIA> print, w1, w2, w3, dw1, dw2, dw3
0.986200 0.993700 1.00000 0.00100000 0.00100000 0.00000