[daip] [!11084]: AIPS - IMAGR: coordinates differ from NVSS more than expected, especially in declination

[Eric Greisen]

Eric Greisen updated #11084
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       Staff (Owner): Eric Greisen (was: -- Unassigned --)

IMAGR: coordinates differ from NVSS more than expected, especially in declination 
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           Ticket ID: 11084
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/11084
                Name: Robert Gray
       Email address: roberthansengray at gmail.com
             Creator: User
          Department: AIPS Data Reduction
       Staff (Owner): Eric Greisen
                Type: Issue
              Status: Open
            Priority: Default
                 SLA: NRAO E2E
      Template group: Default
             Created: 03 October 2017 04:49 PM
             Updated: 03 October 2017 09:00 PM
           Reply due: 05 October 2017 04:49 PM (1d 19h 49m)
      Resolution due: 29 June 2020 12:00 AM (999d 3h 0m)

Hard to say.  There are many potential things to go wrong since this is an instrument that we (or at least I) don't know much about.  My guess would be that its an error in the effective frequency as that will give a radial scaling error in the image but wouldn't say why the effect was primarily in declination.; unless the sources measured were mostly north or south of the center. That is the response of one of the NVSS PIs.  IMAGR grids each channel correctly and then FFTsthe whole to make an image which it cleans.  Unless you ask for frequency dependent algorithmsit then subtracts the same component from each channel (correcting phase for frequency) andrepeats.  I do not understand an error that would affect the center of the field unless the uvw'sare incorrect.  Frequency errors cause position shifts that are proportional to distance from thecenter.  But, as was said above, we know little about the ATA.Eric Greisen


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