[daip] Calibration of polarization spectral line data

[Arno Schoenmakers]

L.S.,

I have encountered a rather serious omission in the AIPS cookbook chapter 4: calibrating interferometer data.

What it comes down to is that if you have a VLA observation carried out in PA or PB mode, that is, with multiple channels but also with 4 stokes parameters, the manual does not give proper hints how to properly incorporate the polarization calibration.

At the top of section 4.7.4 it says that after calibration of the channel 0 dataset (4.4 and 4.5) , the relevant CL table must be copied over to the line dataset with TACOP. 

However, in case you have also calibrated the  polarization in the channel 0 dataset (following  sect. 4.6), then also the AN table must be copied over from the channel 0 to the line dataset otherwise the polarization calibration of the line dataset will not work. A typical error one gets without copying the AN table, for instance in SPLIT, is:
dop06 > SPLIT1: UNKNOWN POLARIZATION PARAMETERIZATION =
dop06 > SPLIT1: PROBLEM WITH SOURCE: B0925+420
dop06 > SPLIT1: FAILED TO SELECT VALID DATA

The necessity to copy the AN table is not mentioned anywhere in that section. It can only be derived from the text in Sect. 4.6 where it states that CLCOR not only changes the CL table, but also the AN table.

Could you please add this in a next update of the CookBook?

 With kind regards,

  Arno Schoenmakers
  System Scientist
  NFRA/ASTRON
  Dwingeloo, The Netherlands