Agenda for meeting Mon, 29 March 1999 at 4pm EST.
Date: Mon, 29 March 1999
Time: 4:00 pm EST (2:00 pm Socorro, 2:00 pm Tucson)
Phone: (804)296-7082 (CV SoundStation Premier Conference phone).
Past minutes, etc on MMA Imaging and Calibration Division Page
Agenda
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For the evaluation of antennas, 86 GHz is much more important than 115 GHz. Arguably, we don't need 115 GHz at all (although I definitely would still like it).
For the first _science_ that gets done with the array, 115 GHz for CO is much more important.
The importance of 86 GHz is to observe the SiO masers. We will use SiO sources and continuum sources (planets etc.) for the first single dish tests, and also for the first interferometric tests.
In a much earlier iteration on choice of evaluation receiver frequencies, I found it hard to think of any good reason to justify 115 GHz at all. In as much as 115 GHz will probably be by far the most important frequency for the MMA, I had (and have) a gut feeling that it would be wise to do at least some tests at that frequency. You could imagine (just, and with considerable creativity) some obscure problem with the antennas that gave a suck-out in gain at just 115 GHz, or perhaps unusually unstable baselines at just that frequency, but which wasn't apparent as a problem at 90 GHz or at 230 GHz. Given that 115 GHz is so important, it would be very embarrassing if we hadn't tested the antenna at that frequency and then later on found there was a problem.
It is important for us to test spectral baseline stability as well as gain at a variety of frequencies, including ~90 GHz and ~230 GHz. 115 GHz WILL also be useful because of the Orion CO line; that line has a peak, narrow in frequency but spatially broad (resolved by our beam), and a plateau that's wide in frequency space but very confied spatially (a point source to the beam.) A measurement of the ratio of spectral peak to plateau is a very good direct way of estimating beam efficiency.
So, I would like us to have some response at 115 GHz with the evaluation receivers. However, the 115 GHz Orion signal is the brightest line in the sky - about 90 K. I'd accept a compromise in sensitivity at that frequecy.
For the measurements on SiO masers ag 86 GHz, signal-to-noise ratio may be a limiting factor, so I'd prefer not to accept a compromise in sensitivity there.
Min put the lastest draft version of his cost-benefit analysis memo on his WEB page .
Leonia says:
Min asked me to calculate dependence of sensitivity loss on the beam width
due to tapering. I have carried out it using the AIPS task IMAGR for
the four configurations including VLA.
The results are given in the adjacent gif plots.
Several comments:
1. Mark supposed that this dependence should be the straight line with slope 45 degrees. This is corect as a first approach. This is of cource correct if the configuration has an ideal uniform UV coverage and if the tapering looks like cutting off the outer baselines.
2. In the general case of tapering this simple dependence is not correct even for an ideal uniform UV coverage.
3. IMAGR provides gaussian tapering with the width UVTAPER as a parameter. It is possible that another type of tapering will give another dependence. But I think the difference should be small.
4. The ring-like array (circle) loses less sensitivity than donuts configuration. This statement is in contradiction with Mark statement (memo 199). The two reason can explain the contradiction:
1) Mark considered the simple type of tapering: cuttoff the outer baseline.
2) Plot of the ring like UF coverage (circle) looks like uniform. But it can be ilusion because of big redundancy: many diferent baseline represented by the same point at the UV plane.
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UPCOMING REVIEW: On or before 31 May 1999 we review results from the OVRO and BIMA phase correction systems.
DECISION: 183 GHz or 22 GHz phase correction?
DECISION: Is a nutating secondary necessary?
DECISION: What is the effect of 1/f noise in the HEMT amplifiers of SIS receivers upon our ability to combine total power and interferometric images into a faithful representation of the sky?
MEETINGS: MAC meeting 14 Apr 1999 at noon. ------
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T. Helfer:
A. Wootten: 12-13 April 43m observing 28 May - 3 Jun AAS 5-9 Jun I99 9 - 13 Jun CSO
J. Mangum:
M. Yun:
B. Butler:
S. Radford: