[daip] [!5234]: aips - Daynumbers from VLBA datasets

[Adam T Deller]

Adam T Deller updated #5234
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Daynumbers from VLBA datasets
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           Ticket ID: 5234
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/5234
           Full Name: Adam T Deller
               Email: deller at astron.nl
             Creator: User
          Department: AIPS Data Processing
       Staff (Owner): -- Unassigned --
                Type: Issue
              Status: Open
            Priority: Default
                 SLA: NRAO E2E
      Template Group: Default
             Created: 28 July 2014 01:13 PM
             Updated: 28 July 2014 01:13 PM
                 Due: 30 July 2014 01:13 PM (2d 0h 0m)
      Resolution Due: 05 August 2014 01:13 PM (8d 0h 0m)



Hi,

I have a large number of VLBA datasets which have multiple correlation passes.  Typically this involves one pass on the primary calibrator and one or more passes on additional targets within the primary beam on some of the sources.  This means that not every source is included in the second and subsequent passes (usually only the target, not for instance the phase reference source, fringe finder etc).  Very occasionally, an observation will start close to midnight, say 23:55.  The first couple of scans might be on various calibrators, and it might be 10 minutes before the first scan on one of the sources which is included in the second or subsequent calibrator passes.  This has the unfortunate effect that when one loads the data into AIPS with FITLD, AIPS day 0 is not the same for all datasets.  And since I typically want to export calibration from the first correlator pass to the other correlator passes (using TACOP, or equivalently TBOUT/TBIN), this is a problem.

I have tried fiddling the reference dayno in the FITS header, UV table, and various other tables in the FITS-IDI files corresponding to the second and subsequent correlator passes, to force them to be the same as in the FITS-IDI file from the first correlator pass.  This seems to work ok, and I can use the calibration tables, but the astrometric positions I obtain from the resultant datasets show significant errors (a large fraction of a mas, much larger than is typical for these observations), so I'm guessing I haven't managed to harmonise all of the day numbers properly - it seems that many of the tables have their own reference day, and trying to figure out what actually set the AIPS reference day in the FITLD code gave me a migraine.  (More sinisterly, maybe I have done everything properly and something else is amiss under the hood of AIPS - but let's hope that is not the case). 

Which brings me to my question: would it be possible to add an option to FITLD to set the reference day?  Then I could simply tell FITLD to use the same reference day for all datasets, and I would be able to transfer calibration with no problems.  Or as an external program to be run after FITLD (REFDAY doesn't fit, too many letters... REFDY? RFDAY?), that would also work fine.

Cheers,
Adam

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