[daip] Re: SDA in VLA datasets

[Walter Brisken]

Douglas,

	Is the form of the artefact stable?  in other words, when imaging 
the days separately, does it look the same?  Forgetting about hardware 
problems for a moment, have you considered the following possible causes 
for the artefact:

1.	Phase errors -- your observations were made at very low 
elevations.  I suspect that the isoplanatic patch size is smaller than 
your field of view, so even self cal might not fix the problem.
Test : image different days / time ranges, and look for variation.

2.	Could there be very large extended emission nearby that is barely
detected by the interferometer?  Test : image long and short baselines 
separately and see if it cleans up in the long baseline image.

3.	Are your antennas shadowing at all?  (fillm will alert you about 
this)

4.	Were the antennas recently reconfigured?  Ken Sowinski might 
know if the baselines put into the data at that time were good or not.


-Walter