[daip] subtle differences in images

[Eric Greisen]

Min S. Yun writes:
 > 
 > I am trying to combine the VLA mosaic observation data with the 
 > GBT data using UTESS.  UTESS runs fine if I use just the VLA data,
 > but it behaves strangely as soon as I offer the GBT data, either
 > as one of the inputs or to be used as the default image.  My
 > suspicion is that the beam information is not fully specified
 > for the GBT data, and AIPS does not know exactly how to interpret
 > "Jy/beam" and the beam information given in the header -- the
 > header for the GBT data says BUNIT is JY/BEAM and apparently
 > has the correct BMAJ, BMIN, and BPA info.  Why do I suspect this
 > is where the problem lies?  When I do a TVSTAT on a VLA image,
 > I get the ususal stats and the total flux information.  If I
 > do the same on the GBT image, I do not get the total flux
 > information nor the "number of pixels per beam" report.  Is
 > there another header information AIPS requires besides 
 > BMAJ, BMIN, BPA, and CELLSIZE to calculate the number of cells
 > per beam?  Thanks in advance for any insight you could offer.
 > 

There are two parameters that may also be looked at - from the explain
for PUTHEAD

'PRODUCT '     Clean product code: 1 - 4 => normal, components,
               residual, points  (integer*2)
'NITER   '     Number of Clean iterations (integer*2) 

I am not sure what UTESS does with the GBT beam - in fact I am not
sure what it should do.  The interferometer images are of the sky
multiplied by the interferometer SD beam at the pointing positions.
But that is probably not the case for the GBT image which would depend
on how you got it.  We have no knowledge of the shape of the GBT
beam.

ERic Greisen