[daip] [!7724]: AIPS - AIPS UVPLT option rotated uvdist is weird

[Eskil Varenius]

Eskil Varenius updated #7724
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AIPS UVPLT option rotated uvdist is weird
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           Ticket ID: 7724
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/7724
           Full Name: Eskil Varenius
               Email: varenius at chalmers.se
             Creator: User
          Department: AIPS Data Reduction
       Staff (Owner): -- Unassigned --
                Type: Issue
              Status: Open
            Priority: Default
                 SLA: NRAO E2E
      Template Group: Default
             Created: 11 December 2015 10:24 AM
             Updated: 11 December 2015 10:24 AM
                 Due: 15 December 2015 10:24 AM (4d 0h 0m)
      Resolution Due: 21 December 2015 10:24 AM (10d 0h 0m)



Dear helpdesk,
I'm calibrating EVN data with a very elongated calibrator source (called J1232). Hence I thought it would be interesting to look at the UV-data along the elongation axis. I was happy to find the option bparm=17,0 and ROTATE=65 (degrees from image) which should be useful for me. However, this option makes UVPLT behave unexpectedly. First, note that with the EVN there are no baselines shorter than 2Mlambda in these data. This is clear also from ordinary UVPLT with bparm 0, as well as bparm 6,7,2,0 for uv coverage (see attached files).

Now, when I look at the data with UVPLT bparm=0 I see a complex structure. From the image, two points dominate so I would expect clear beating if I plot the data rotated along the elongation axis. This is also nicely shown by UVPLT, BUT: now the uvdist axis goes all the way to 0. This is weird!

I think that there are two possible ways UVPLT could show the data with bparm 17: Either rotate the whole UV-data, or just plot a slice along the rotation axis. In either of these, the minimum baseline should never be shorter than 2Mlambda. I see a similar behaviour also on another data set, so I think this should be reproducible on any dataset.Could you explain what is going on here? The rotation option would certainly be very useful if it works properly. Perhaps I'm just misunderstanding what is shown, but I'm certainly puzzled.

Best regards,
Eskil

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