[daip] 3C 48 model

[Jim Ulvestad]

Hi Amy et al.,

I'm reducing a data set from 2002, A configuration, X band,
with 3C 48 as the only flux calibrator, using VLACALIB.
VLACALIB is clearly picking up the model, as I get a new
image/CC file for 3C 48 showing up in my directory every
time I run it.

But I'm getting many amplitude closure errors in the 10-20%
range, concentrated in the antennas on the North arm.
The source was not observed exactly at transit, but about
2.25 hours from transit.  There is an adjacent calibrator
at 0151+277 (4 deg. away in RA, 6 deg. in dec.), observed
5 minutes apart, that shows no errors at all, leading me
to believe this shouldn't be atmosphere.  Over a 3.5
minute scan, the phases do reasonably well, wrapping up
to 30-40 deg. on some baselines, more typically 20 deg.
or so.

I can't find any bad data in LISTR, though I will look
a little bit more.

Yes, I did run SETJY first.

So my question is, have you typically seen this level of
amplitude closure problems on 3C 48 even with your model?
I recall that X-band A array used to be a kind of bad
circumstance to use 3C 48 in; the calibrator manual says
to use only the inner 2 antennas.  Is it possible that the
source has enough structure that the model just doesn't do
well enough?

Thanks,

Jim