[daip] [!12656]: AIPS - Offset source moving in RA during observation

[Andy Biggs]

Andy Biggs updated #12656
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Offset source moving in RA during observation
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           Ticket ID: 12656
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/12656
                Name: Andy Biggs
       Email address: abiggs at eso.org
             Creator: User
          Department: AIPS Data Reduction
       Staff (Owner): -- Unassigned --
                Type: Issue
              Status: Open
            Priority: Default
                 SLA: NRAO E2E
      Template group: Default
             Created: 07 September 2018 04:11 PM
             Updated: 13 May 2020 06:45 PM
           Reply due: 15 May 2020 01:57 PM (1d 19h 11m)
      Resolution due: 27 April 2022 12:00 AM (713d 5h 14m)

Here is a similar plot to that which I posted before - it shows the position of B (which is nearly a point source) as a function of time. This is in the full self-calibrated dataset (A+B) before I subtract the clean components corresponding to the brighter image (A). The variation is pretty symmetrical which is what worries me. The smaller locus of points is the position of B (using modelfit in difmap) in the B-only dataset after it has been self-cal'd. B now wanders much less and the line points towards the weak jet in this image so I think this is pulling the fit in some systematic way. Anyway, it can be seen what the self-cal is having to overcome to make a decent image in B.
Interestingly, the previous plots for the VLBA data showed B shifting mainly in R.A. and in the opposite direction. I've no idea if that's significant.
Andy

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