[daip] [!13137]: AIPS - DTSIM, possible problem with Dterms

[Thomas Krichbaum]

Thomas Krichbaum updated #13137
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DTSIM, possible problem with Dterms
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           Ticket ID: 13137
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/13137
                Name: Thomas Krichbaum
       Email address: tkrichbaum at mpifr-bonn.mpg.de
             Creator: User
          Department: AIPS Data Reduction
       Staff (Owner): -- Unassigned --
                Type: Issue
              Status: Open
            Priority: Default
                 SLA: NRAO E2E
      Template group: Default
             Created: 10 December 2018 05:31 PM
             Updated: 10 December 2018 05:31 PM
           Reply due: 12 December 2018 05:32 PM (2d 0h 0m)
      Resolution due: 05 September 2021 12:00 AM (999d 6h 28m)

Hi Eric,I did some more tests using DTSIM. I think there may be a problem. I run a DTSIM simulation using a single Gaussian point source. For simplicity I specified a D-term only for one antenna (PT) and one polarisation (FEED_1R nonzero, but FEED_1L=0). For all other VLBA antennas the D-terms were set to zero. I tested both, w/o LINPOL. I do expect that the cross-hand phases for PT are affected by the D-term, but not the parallel hand phases. When I inspect the  LL or RR phases, however, the parallel hand phases to PT are nonzero (with opposite sign for RR and LL). The amount of phase offset is a bit strange. For a ~5% DTERM I would not expect the phases deviations be so large. See attached phase plots with PT high-lighted. There is also a plot for Stokes 'I', which shows an unexpected large amplitude offset for PT.I rerun DTSIM changing the DTERMS for PT. Funnily, this has no effect on the station phase. They come out the same.  The DTSIM input file is attached.Do you have any idea what is going on and is it possible to fix it ? I am not the expert on polarimetry, but perhaps the error may occur in the SUBROUTINE DTERM.kind regards, Thomas

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