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

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Eric Greisen updated #12656
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       Staff (Owner): Eric Greisen (was: -- Unassigned --)
              Status: On Hold (was: Response Overdue)
           Reply due: - Cleared - (was: 11 June 2020 01:11 PM)

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): Eric Greisen
                Type: Issue
              Status: On Hold
            Priority: Default
                 SLA: NRAO E2E
      Template group: Default
             Created: 07 September 2018 09:11 AM
             Updated: 13 May 2020 11:45 AM
      Resolution due: 05 March 2023 05:00 PM (998d 2h 53m)
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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