[mmaimcal] stephane's draft memo

[Min Yun]

I have some comments and questions on Stephane's draft memo.  I would
appreciate any enlightening comments or suggestions.

1. The third eq. on page 1 has a factor "2" in front because of "ON-OFF".
If we do OTF, this factor would be closer to 1 than 2, wouldn't it?
If so, much of the concerns in the rest of his section 1 is reduced by
a factor 4, and the situation may not be nearly as bad as it is stated.

2. In page 3, 1st paragraph, it says "Hence, signal to noise ratio
would be much higher on the shortest baselines, although the accuracy
of the flux determination would still be limited by the calibration
accuracy."  I think these are two separate questions, and we need to
be able to have BOTH accurate calibrations AND the ability to make
high S/N measurements.  I would not want to loosen the requirement
for high S/N measurements because we are limited by calibration accuracy.
(Just talking out aloud here....)

3. In page 3, 3rd paragraph, it is stated that "a deficit in the distribution
of weights between D/2 and 5D/4" results from a homogeneous array.  From
his Figure 1, it seems the deficit is actually between 4m and 11m, or
D/3 and 5D/6.  What is my confusion here?  Also, does he mean to make
a case for the 8m antennas from Figure 1?  It hardly seems convincing,
and I would argue that the 8-m antenna does a pretty poor job of 
filling in between 3m to 8m scale things.  (It says "6-m antennas 
would provide a somewhat better match for the weight distribution" 
in page 7....)

4. Repeating Steve and others' comments, the justification for favoring
the 8-m antenna in section 3 seems extremely scant.  The incredible
sensitivity of ALMA over the existing arrays not only come from the
increase in the total collecting area but also from the better site and
the overall noise performance of the individual telescopes.  This would
be even more important at higher frequencies where the effective
collecting area falls off quickly due to aperture efficiency loss,
and a lot could be made up by having smaller antennas with far more
accurate surface.


					-- Min