[mmaimcal] Re: solar and stellar observing modes

[Al Wootten]

Hi, Arnold

Thanks very much for your efforts.

I think the compact array, if we go ahead with it, can address the
short baseline issue to some extent.  I can bring this up when we discuss
it.  One proposal is for about a dozen 6m antennas, which will give
both a good primary beam (~6') at the longer wavelengths and good short
spacing recovery, particularly at higher frequencies where the 12m primary
beam is quite small and pointing and other problems may be more difficult
with 12m antennas.

Bastian and others have requested before to have:
       at least 2 frequency bands simultaneously (better more)
 but I think this will not be possible, though there will be quite short (few s)
 time periods between changes in frequency.  One exception is that the
 183 GHz water vapor radiometer will always be on in the current design.
 However, it will be off axis, so not pointing to the same place in the
 sky (by 3' or so in some current designs).  It is envisioned that the 3mm
 receiver will always be on, but that the optics train will only illuminate
 one receiver at a time, so that the shortest intervals between observations
 will presumably be between 3mm and another frequency of choice.

It will be possible to:
      combine with telescopes on the Canary Islands (observe close to
horizon in Chile)
but we have pretty good elevation limits--primary operating conditions
include an elevation range of 2 degrees to 89.8 degrees.  We will run ALMA
(or a single antenna) in conjunction with very long baseline experiments.

There will probably be circular polarization feeds at the lower frequencies,
and circular polarization provided through suitable combination at higher
frequencies.

I think you are correct; the items in your list with these few exceptions
can be achieved with the current design.

Clear skies,
 Al
+--------------------------------------------------------+
| Alwyn  Wootten   (http://www.cv.nrao.edu/~awootten/)	 |
| Project Scientist, Atacama Large Millimeter Array/US   |
| Astronomer, National Radio Astronomy Observatory       |        
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