[daip] Convolution

[Eric Greisen]

Volker Heesen writes:
 > Dear Dr. Greisen,
 > 
 > I ask you for help with some technical problem when using AIPS. I have 
 > combined several cleaned maps with the task LTESS. The maps had all the 
 > identical beam. The resulting map indicated to consist of POINTS (that 
 > is displayed by IMH). When I convolve the map with a clean beam using 
 > CONVL the resulting beam is not the one I prescribed with BMAJ, BMIN and 
 > BPA. It is larger than that. I checked that with a point source with 
 > IMFIT. Moreover the flux of point sources is decreasing when convolving, 
 > which should not be the case. I tried to set the header PRODUCT on 1 to 
 > get a NORMAL map (NITER = 1) or DIRTY map (NITER = 0) instead of POINTS. 
 > But that does not change the result of the convolution.
 > 
 > Any help on that subject is warmly welcome!
 > 
 > best regards,
 > Volker Heesen

I am not that familiar with LTESS, preferring FLATN myself.  However,
if you combine Cleaned images then the points are already convolved
with a Clean beam and should need no further convolution.  LTESS
forces the output header tio say (erroneously) points (type 4) when it
should say whatever is correct for the type of input image.

The flux of a point object should not go down with CONVL but it is
true that scaling with that task is tricky and may not be 100% correct
since it does change the beam size.

Eric Greisen