[asac] Report on ALMA-J Activities

[kawabe ryohei]

Dear folks, 

Today, I will not be able to attend the ASAC telecon, because
I will be on so-called Golden-Week vacation
Here is a report on the recent ALMA-J activities for major ACA science 
issues. 

1) ACA configuration & antenna positions
  We are trying to consolidate ACA configuration and to propose 
 the final position (x, y, z) of each ACA antenna based on 
 two configurations approach, which is composed of
 so-called Inner Array (with a north-south axis ratio of 
 1.1)  and North-South (NS) Array with a ratio of 1.7
  (See ALMA memo No. 538 by Morita & Holdaway). 
 The location of ACA is called North Position, where is 
 140 m north from the center of the 12m array compact 
 configuration (see a memo on combined array by Iono et al. circulated 
before). 

2)	Combined Array Simulation
Recently, Ed Fomalont proposed that the combined array will be the default 
mode of the 12m array and ACA, and Jack Welch supported him, although the 
combined array is not always used for coordinated observations. This is not 
quite different from our original idea/plan that the coordinated 
observation mode is a major mode, and ACA stand-alone and combined array 
modes are minor. One issue is integration times needed for the 12m Array 
and ACA. Our original plan is based on the assumption that ACA should 
observe target sources four times more compared to the 12m Array ( 2.5 
times more for 50 antennas case) to equalize sensitivity in uv domain. In 
case of the combined array mode, we get the same integration time for the 
12m array and ACA, but the ACA integration time might not be sufficient for 
high fidelity imaging. Then, we are now performing simulation to see what 
is “time evolution effect of image fidelity” by changing the integration 
time of ACA using GILDAS and MIRIAD. We can report on the preliminary 
results soon. 

3)	Study for Standard Horn absolute calibration method  
We are studying the scientific validity of the Standard horn method 
proposed by Gibson and Welch for ACA. We will also report on this soon.

4)	Revision of ACA documents
Two documents,  “ACA Scientific Specifications and Requirements”,  and 
“ACA Calibration Specs and Reqs” are under revision according to 
discussions in the Science-IPT and calibration group. We also developing 
ACA Operation Plan document based on “ACA Operation Concept”, and this 
will be finally merged with ALMA Operation Plan. 

5)	Other issues
 We are also working on the following issues 
- Scattering cones for TP and 7m Arrays
- Simulation of dual-loads and single load calibrations
- Beam shape calculations of the ACA stand-alone mode for two 
configurations
- ACA Ancillary calibration device plan; 183 GHz scanning radiometer, 
short-baseline radio seeing monitors, 10 micron cloud monitor etc. 


Regards,

Ryohei

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