[alma-config] Size of model sources

[Min Yun]

Hi Adrian,

John has also previously expressed his desire to modify the input images 
to better match the arrays we want to test.  I do not have any 
fundamental objections to such suggestions.  However I want to avoid
tailoring input images too much to match the arrays because we cannot
do this in real life.  Clearly the current Cyg A image is a poor match
for the A-array as the simulated images show.  
Well, finding this out was one of the goals of the
exercise -- granted, this was an easy one to predict.
As I told John before, one of the key motivations for having the five test
images was to have enough diversity among them to account for some of
the images being less than ideal for testing any particular array.
It has been pointed out previously that one can come up with an array
best taylored for any particular test image even though it may not be
the best one in general.  Some ignorance may not be such a bad thing
in this case.  



					-- Min
					
					
p.s. The Cyg A image does have structures at larger scales as you
might have seen in my simulated observations.  You have
to look past the bright hot spots to examine them, however.  We also
need to figure out good ways of examining these images at all scales
with a good dynamic range.


> Folks,
> 
> I have one suggestion to make, that comes from looking at Steven's recent
> mapping simulations. The A-array maps of Cyg A only show the two bright hot
> spots, one in each lobe, and this does not seem too sensible to me. Surely
> we chose the various sources to give the sort of balance of structure on
> various scales, across a wide range of scales, that might be met in practice
> with ALMA. But only the small end of the scale has much effect in this case.
> 
> Should we not shrink the size of Cyg A, as might be done by moving it to
> greater distance, so that the whole range of scale sizes gets sampled. What
> I have in mind is scaling the source (and indeed any other source model) so
> that the overall diameter (i.e. about 2 arcmin in the case of Cyg A) is
> reduced to match roughly the diameter of the primary beam of the ALMA dishes
> FWHM, at whatever observing frequency is adopted. I think this will give a
> much more useful test of the different antenna configurations.
> 
> Cheers
> 
> Adrian
>