In response to Charge Number one from the Board:

1. Recommend clear, science-based criteria to be used by the Project
in preparing tradeoff studies should budgetary constraints make
it necessary to reduce planned activities in the baseline project
following analysis of the responses to the antenna procurement
process.

the ASAC has asked for a number of simulations.  Their request follows.
I have asked Mark Holdaway to estimate the Science IPT resources
required for this set of simulations; he estimates it will take about a
week.  We think that we can perform these simulations, which may prove
useful, and still maintain the baseline schedule.  Mark has considerable
experience with simulations and this will not require development of new
software; we will use our existing configuration-testing image library.
We will not be able to optimize the arrays of smaller number of
antennas, however, as this would require significant additional
resources.  As you know, ALMA is optimized for 60 antennas in the
approved configuration.

The proposal from the ASAC:

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One of the primary science requirements of ALMA is that it produce images
of high quality, comparable to those produced by HST and large ground-based
telescopes. The ASAC is considering the issue of how the quality of images
produced by ALMA varies as a function of the number of antennas, N. To
consider this question, the committee needs to have simulated imaging
experiments performed, such as were developed during the design phase of
ALMA.

The committee requests that the ALMA Science IPT rerun the imaging
simulation
program of Pety, Gueth, & Guilloteau for a well defined and fixed set of
parameters so that the effects of changing N can be evaluated.

The simulations should be run with the following inputs.

  Fixed parameters:
       Frequency: 300 GHz
       Resolution: 0.1"
       Track HA range: pm 2 hours
       Source:  From the Pety et al test images
                 http://www.iram.fr/~alma/node12.html

  Varying parameter:
       N = 48, 51, 54, 57, 60, 64

These parameters should place stringent limits on the imaging capability of
the array. If the Science IPT feels that other values for these parameters
might provide a more rigorous test, they should feel free to change them
so long as they remain fixed for all the simulations so that the results for
different N can be directly compared.

The antenna configurations will have to vary to maintain 0.1" resolution
as N
varies: this is unavoidable. The resolution should remain fixed since this
is the quantity of interest to the observer.

These simulations are for the baseline project only, which is the 64
antennas
without the ACA.

If possible, the simulations should be run on 2 or 3 model sources
to test a range of imaging options, but it is important that the
ASAC have test results in hand soon for at least one source.

The outputs of the Pety et al. software as presented in ALMA memo 398
are sufficient for the purposes of the ASAC.

The simulations will be most useful if they can be available to the ASAC
before its meeting in Charlottesville on 27-28 September.

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