[daip] GETJY

[Jim Ulvestad]

If you look at the solutions for 1748-253, not only is the flux high,
but the rms/flux ratio is far too high.  I'm pretty sure this is due
to bad data, which may be due to cross-talk from antennas close to
each other.

In FILLM, CPARM(4) gives you the option of dropping data that are
shadowed, and you could try putting in a value of something like
50 meters to see if that makes things better (by getting rid of
data when antennas might be cross-talking).  However, it's better
to actually look at the data and see what's going on (next 
paragraph).

I would be very surprised if you didn't have huge closure
errors when running CALIB/VLACALIB.  This would be caused
because some short baselines would have huge amplitudes,
but the amplitudes on the longer baselines would be much
smaller, so there would be poor closure in the solutions
for individual antennas.  If you have huge closure errors
reported, you can use them as a guide to decide which antennae
to flag.

If the closure errors don't help enough, the next option is
to actually calibrate the data using CLCAL, then plot up the 
amplitudes of the calibrated data to see where they're high.
You can then CLIP or UVFLG the high amplitudes, use SETJY
to zero the flux of 1748-253, then go back and run CALIB
again.

What you will generally need to beware of is that even if you
flag the high amplitudes on 1748-253, you may have similar
bad amplitudes on your program source.  So what I would do
after getting the calibration of 1748-253 correct is to
split the data, make a UVPLT on your program source, then
CLIP the high points.

jim ulvestad
John Keck wrote:
> 
> I was wondering if you might know what the cause of my problem is and how
> I can correct it.
> 
> The problem is with GETJY on one of the several C-band observations I'm
> calibrating.  It gives a flux that's about 20 times too high:
> 
> boheme> GETJY1: 1748-253        :  0   C     1   11.20408 +/-   7.62896
> boheme> GETJY1:                              2    5.51208 +/-   3.54104
> 
> I'm pretty sure that I'm using the correct procedure because the flux of
> the other phase calibrators of the observation aren't that far off:
> 
> boheme> GETJY1: 1923+210        :  0   A     1    1.38879 +/-   0.03630
> boheme> GETJY1:                              2    1.48411 +/-   0.04156
> boheme> GETJY1: 2013+340        :  0   T     1    0.92656 +/-   0.01559
> boheme> GETJY1:                              2    0.92186 +/-   0.01529
> 
> The observing log (AM447, 94Feb17), says that a couple of the antennas
> were having problems, and that there was some shadowing that corrupted the
> data, so perhaps that is the cause.  I can't seem to find anything in the
> Cookbook about shadowing.  What should I do to correct it?
> 
> Thanks,
> 
> John Keck