[mmaimcal] Brown message on small antenna array

[Min Yun]

Al,

There is a general enthusiasm for the ACA within the project, and
it reflects the overwhelming concern over the ability to incorporate
the total power measurements with the cross-correlation data.
I am no exception to this sentiment, and my immeidate gut feeling
is to go with a bunch of 6m diameter antennas.  Several members
of the ASAC are questioning the motivation for the ACA, however,
and we should not take this issue lightly.  I agree with Ritcher
and others that we should not throw our money into this project
only because it appears to be an immediate and obvious improvment
idea.  The ASAC seems to lean towards a more comprehensive review
of the topic, and I also believe this is what we should do.

First of all, the standard set of equations we have used thus far,
such as cost or some sort of efficiency, should be thrown  out since
we do not expect these smaller antennas would cost less.  A more
important issue is what we hope to accomplish fundamentally, and
in this respect we should be open to any new ideas including a
large single dish antenna.  We need to examine more rigorously
what the true imaging benefit is and how best to accomplish it
-- configuration design would be important (e.g. shadowing).
Ability to cross-correlate with the 12m antennas should be 
evaluated more rigorously -- what are the added costs? what are
the expected complications?  would CARMA work these out by the 
time we need to worry about it?  

If we adopt the ACA, should it be located at a different location?
How bad is the cross-calibration problem?  It may be no worse than
calibrating the long baselines in the standard arrays.  We should
be able to address this problem once we are able to locate a
reasonable candidate locations.  Such an arragement would offer
an attractive addition to the 10+ km array if we can phase up
the small antennas and cross-correlate with the rest of the array.

Morita-san has done some work on the configuration design for the
ACA, and we can ask him to pursuit this further.  As for the
overall merit of the concept itself and other competing ideas,
we C&I group should give it a little bit of focussed attention.
Can we make this the topic of our discussion tomorrow unless there
is a more pressing issue?  Can everyone come up with a list of
issues that are relevant and possible ways to tackle them?
I would feel much better being proactive about this issue than
having someone else telling us what to do or what decision is
made based on some vaccum argument.  I have to write a couple
of reports on the strawperson configurations, but this may not
be a lot of additional work if we can all work together.




					-- Min