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

[Adam T Deller]

Adam T Deller updated #5234
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              Status: Open (was: Closed)

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): Eric Greisen
                Type: Issue
              Status: Open
            Priority: Default
      Template Group: Default
             Created: 28 July 2014 01:13 PM
             Updated: 03 April 2015 03:24 PM



Hi Eric,

As I mentioned in a mail earlier today, I have found that while this fix certainly improves matters, there is still an astrometric offset in the datasets where the target FITS file starts on a different day to the calibrator FITS file.  The offset is primarily in right ascension, and is fairly small (~1 milliarcsecond), but this is 20x bigger than the expected uncertainty.

I have checked and the CL tables which are being produced in the two datasets are basically identical in phase at least.  I do still need to check whether the delay values (and dispersive delay; maybe TECOR is at fault?) are also identical.

I've done quite some searching through for differences, and the only thing I have come up with so far is that the RDATE in the MC tables, CT tables (and possibly others) are different: they have the original start dates, not the REFDATE specified in FITLD for the case of the late-starting observation.  However, the time entries in the MC/CT table are correct relative to the FITLD REFDATE: i.e., they are the same in both datasets.  To summarise: the contents of the MC/CT table are consistent relative to everything else in the dataset, but inconsistent with the RDATE value in the MC/CT table header.

Do you know if the times in the MC/CT table are being taken relative to the RDATE in the MC table header anywhere?  That could certainly lead to problems.  One place I could imagine might be CLCOR for the EOP update.  But then it should have showed up in the phases of the resultant CL tables, I would have thought, and that doesn't appear to be the case.

I can provide datasets that demonstrate the problem, but it is kind of subtle and the sources are not hugely bright or anything.  Please let me know what additional information would best help you investigate further.

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