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<DIV><FONT color=#000000 size=2>To Bryan's point</FONT></DIV>
<DIV><FONT color=#000000 size=2> <FONT color=#000000>1) given
a fixed physical size limit, what flavor of array would you design
then?<BR></FONT></FONT></DIV>
<DIV> </DIV>
<DIV><FONT color=#000000 size=2> <FONT size=3>That is indeed
the right question, beyond any doubt</FONT></FONT></DIV>
<DIV><FONT color=#000000 size=2><FONT size=3></FONT></FONT> </DIV>
<DIV><FONT color=#000000 size=2> <FONT size=3>2) now, if
you can come up with a ring/donut which has nearly as good an
imaging<BR>capability as the more condensed spiral, and that has twice the
resolution,<BR>which would you choose?<BR></FONT></FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT> </DIV>
<DIV><FONT color=#000000 size=2> My reply to that is that
having "as good imaging capability" and "twice the
resolution"</FONT></DIV>
<DIV><FONT color=#000000 size=2> is a conflicting request. To get
resolution, you have to sacrifice something (brightness</FONT></DIV>
<DIV><FONT color=#000000 size=2> sensitivity, sidelobes, deconvolution
stability, ...). The best of both worlds does not exist,</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT><FONT size=2> so that we have to
define an acceptable compromise.</FONT></DIV>
<DIV><FONT color=#000000 size=2> </FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT><FONT size=2> That's our job.
Moreover, w</FONT><FONT color=#000000 size=2>e don't have yet the definition of
"good imaging quality" (as</FONT></DIV>
<DIV><FONT color=#000000 size=2> pointed out by Eric Keto, current
estimates of image quality may depend on the imaging tool)</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT> </DIV>
<DIV><FONT color=#000000 size=2>To Min's argument</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT> </DIV>
<DIV><FONT color=#000000 size=2> 1) I had somehow in mind that nobody
ever disputed that even the 3 km "configuration" had</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT><FONT size=2>to be a ring-like or similar
thing. </FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT color=#000000 size=2>2) Concerning brightness, the compact array only
gives you optimal brightness at the largest</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT><FONT size=2>angular scales. Our problem
is mostly multiscale (see below)</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT color=#000000 size=2>3) The resolution is not an absolute
number because distance convert it to different angular</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT><FONT size=2>scales... So we have to
figure out if among the limited range of resolutions we can afford</FONT></DIV>
<DIV><FONT size=2>given the site, there is any PHYSICAL value which makes a step
in our astronomical knowledge. This can occur for various reasons (e.g.
the distance to the nearest star,</FONT></DIV>
<DIV><FONT size=2>nearest star formation region, nearest galaxy,
etc...) Once we get such a number, </FONT></DIV>
<DIV><FONT size=2>we could try to optimize imaging quality for this number
(sensitivity + deconvolution error</FONT></DIV>
<DIV><FONT size=2>amplification)</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT color=#000000
size=2>
Stephane</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT> </DIV>
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