[daip] [!5455]: aips - CALIB task for amplitude self-calibration : How the details are implemented ?

[Jae-Young Kim]

Jae-Young Kim updated #5455
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CALIB task for amplitude self-calibration : How the details are implemented ?
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           Ticket ID: 5455
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/5455
           Full Name: Jae-Young Kim
               Email: jykim at astro.snu.ac.kr
             Creator: User
          Department: AIPS Data Processing
       Staff (Owner): -- Unassigned --
                Type: Issue
              Status: Open
            Priority: Default
                 SLA: NRAO E2E
      Template Group: Default
             Created: 05 September 2014 06:57 AM
             Updated: 05 September 2014 06:57 AM
                 Due: 09 September 2014 06:57 AM (4d 0h 0m)
      Resolution Due: 15 September 2014 06:57 AM (10d 0h 0m)



To whom it may concern,


hello,

My name is Jae-Young Kim and I'm a graduate student at Seoul National University, Korea.

I'm currently dealing with a VLBI polarization experiment, which has only three antennas.
Now I'm writing down this to ask about some details of the CALIB procedure.

To construct maps of full Stokes parameters, I'm now solving for a subtle difference between L/R pol gains.
The purpose is to make the circular polarization V ~ 0, so that information on linear polarization can be extracted well.

My workflow is as following.
(i) First I made a Stokes I map in Difmap. 
Then (ii) the map is loaded by AIPS and is used for CALIB task to self-calibrate UV data of the source.
At this point I set SOLMODE = 'A&P' so that both amplitudes and phases can be calibrated.
After this (iii) I export the data to my working directory and continue mapping Stokes I,Q, and U in Difmap again.

Actually, I'm just a bit worried.
I found that this method can makes V ~ 0, which looks good for practical purposes.
But I can't understand what is going on in the CALIB task. 

As far as I know the amplitude self-calibration can be done only when there are at least 
four antennas to make the amplitude clousure, which is similar to make phase closures with at least three antennas. 
But in AIPS CALIB the amplitudes seem to be corrected well for my purpose.

So, I would like to know how CALIB does the amplitude calibration even when there are only three antennas.
If it does not raise any serious issues then I'm going to do the calibration for many sources in this way.
But if the calibration could go wrong then I would like to find another way.

Could you please let me know how CALIB with SOLMODE='A&P' actually works in AIPS ?


Thanks and regards,

Jae-Young Kim

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