[daip] New Ticket - [!SHZ-259033]: Archive file changes?

[Jacqueline Hodge]

New Ticket: Archive file changes?

Hi there,
I'm having issues trying to reduce the fifth data file for project AR708 using AIPS (31DEC10 version).  Following exactly the same steps, I get a different answer than someone who reduced the data right after it was taken with the EVLA.  I'm not new to AIPS, and I'm fairly certain I'm not making a newbie mistake, (although I hope that's the problem because that would be easier to fix.)  I am told that they got the file sent to them directly after some problems were fixed by NRAO people (such as the antennas continuously taking data, including off source, and incorrect online opacity corrections.). I, on the other hand, downloaded mine from the archive within the last week or two.  Is it possible that the archive file has been altered in the time since the first reduction?  Or that the expert NRAO people did something to the first data file that I don't realize I need to do to the archive version?  I've been referring to the new EVLA chapter in the AIPS cookbook, but I contin!
 uously get a different answer than the previous reduction.  

The differences I get are odd, too.  For example, using 'CALC' and the defaults in SETJY, as the previous person did, I get a *different* flux density for the primary calibrator.  The difference is small, but this is odd, since it's the same data taken at the same frequency...  

Then, when trying to use QUACK to flag the first 5 seconds of each scan, the task tells me that it successfully flagged 11.33 minutes of data, but I see nothing in the FG table (of which there is only one version).  I ended up flagging the the first 5 seconds by hand with TVFLG.

Finally, after (supposedly) the same flagging and calibration procedure, I get a flux density for the secondary calibrator that is twice what the previous reduction found.  And the resulting amplitudes look horrible....as if the amplitude calibration didn't work, or there was still tons of bad data in the dataset.  Even more strangely - I reduced another file from the same project code, and I also got a flux density twice as high for the secondary calibrator.  I've tried fiddling with all sorts of methods/parameters/flagging, and my results stay the same.  

So sorry to bug you with this long email, but I'm about out of ideas.  This doesn't explain the setjy difference, but is it possible that the dataset still has off-source data contaminating it?  Or, do you know if the problem with the online opacities for these data have been fixed, and if that could cause a factor of two difference in the phase calibrator flux density?

Thanks in advance,
Jackie

ps- I am including my reduction notes.  I've tried doing things in other orders, (like BPASS before CALIB) but I still get the same results.  

Ticket Details
===================
Ticket ID: SHZ-259033
Department: AIPS Data Processing
Priority: Default
Status: Open
Link:  https://help.nrao.edu/staff/index.php?_m=tickets&_a=viewticket&ticketid=477
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