MMA/ALMA Imaging and Calibration Group Meeting 12 Apr 1999

MMA/ALMA Imaging and Calibration Group

Agenda for meeting Mon, 12 April 1999 at 4pm EDT.

Date: Mon, 12 April 1999

Time: 4:00 pm EDT (2:00 pm Socorro, 1:00 pm Tucson)

Phone: (804)296-7082 (CV SoundStation Premier Conference phone).

Past minutes, etc on MMA/ALMA Imaging and Calibration Division Page

Agenda

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Meeting Status - Wootten

Take a gander at registration and tell me what you think.

Owing to a conflict with the meeting of the Japan Astronomical Society fall meeting an attempt was made to rearrange meeting dates but it was found to be impossible, mostly owing to the difficulty of locating hotel room blocks in Washington during the Fall. The meeting will be held 6-8 October 1999. Science with a Large Millimeter Telescope Array will be an international conference on the occasion of the planned signing of a Memorandum of Understanding to combine North and South American, European and Asian plans for construction of a large array of millimeter telescopes into a single large project. It will begin with a demonstration and reception for members of Congress in the Capitol at 5:30 pm Wednesday, 6 October 1999. This will be at 23/25 Rayburn. We have this room from 4:30-5:30 for setup, during which an LOC subcommittee will arrange a computer link through which to demonstrate remote observing to the NRAO 12m and/or other telescopes wishing to participate. There will be a display of the Chajnantor site; retrieval of data in real time from the site was judged to be too risky to attempt. There will be a display of the high technology parts of receivers. There may be room for some poster displays. Food and drink will be arranged with the House caterers. Attendees are invited to invite their congressional representatives to attend and to explain the project to them. Gene Runion and Jeff Mangum, of NRAO, will arrange technical matters including internet access to the room and computer availability. Kevin Marvel will act as liason to the Congressional staff. The room has been arranged by Billie through Rep. Ehlers, of the House Science Committee, with his Assistant Loraine Kehl as the point of contact. Carol Whitley will arrange for food service with the House caterer. Lectures and posters will be presented at the Carnegie Institution of Washington, 1600 P St. NW. Accommodations have been arranged at the nearby Omni Shoreham Hotel for the period including the nights of 5 Oct through 9 Oct. The number of rooms in the block (at $149) is: 50 for the 5th, 150 - 200 for the 6th, 200 for the 7th, 150 for Friday - 10/8 125 for Saturday - 10/9 The banquet will take place at the hotel on 10/7/99. The MAC/SAC/JAC meeting will take place in a meeting room there on 10/9/99. A press conference will begin the proceedings at 8am, to explain the world collaboration to the media and the public. The scientific proceedings will follow at 9am. Posters will be displayed in the reception area just outside the lecture hall. We will need to identify appropriate caterers for the coffee services here, as well as locate poster boards to rent for the reception room. The purpose of the conference will be to highlight the science that this powerful world array will accomplish, with particular focus on: -Investigation of galaxies near the time of their formation -The formation of stars -Detection and study of planets and disks forming them around nearby stars -Study of the origin, distribution and evolution of the elements and their isotopes The conference will be organized and hosted by Associated Universities, Incorporated and the National Radio Astronomy Observatory. The Scientific Organizing Committee is composed of Ed Churchwell, John Bieging, Geoff Blake, Roy Booth, Bob Brown, John Carlstrom, Ewine van Dishoeck, Neal Erickson, Neal Evans, Yasuo Fukui, Stephane Guilloteau, Mark Gurwell, Tetsuo Hasegawa, Richard Hills, Masato Ishiguro, Ryohei Kawabe, Gill Knapp, Karl Menten, Jim Moran, Steve Myers, Naomasa Nakai, Luis Rodriguez, Larry Rudnick, Peter Schloerb, Peter Shaver, Jean Turner, Malcolm Walmsley, Eric Wilcots, Al Wootten (Chair), and Satoshi Yamamoto. Science with a Large Millimeter Array will be limited to 200 participants. Information will be posted on the Millimeter Array web site with the URL http://www.mma.nrao.edu/science99.html At this time, the information is located at http://www.cv.nrao.edu/~awootten/mmaimcal/science99.html I am currently setting up the registration page and mailing invitations to the speakers. The WWW pages do not list the speakers, pending their invitations being issued and accepted. The list of prospective speakers which we have arrived at may be found at http://www.cv.nrao.edu/~awootten/mmaimcal/schedule.htm (no 'l' on the end).

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ALMA Status - Wootten

The NSF and European Agency representatives agreed on a name for the joint array: Atacama Large Millimeter Array (ALMA). Alma is the Spanish word for soul.

Brown reported: On March 30 the NSF and the European Negotiating Team initialed a Memorandum of Understanding for a joint design and development program. Once signed in a matter of weeks, this MOU will govern the D&D program for the next 2 years. It sets out a management structure headed by a project coordination committee to be composed of six individuals named by the NSF and six named by the European Coordinating Committee. The Project itself will be managed by an Executive committee made up of the MMA Project Director and Project Manager and the LSA Project Manager and Project Scientist. A joint science and technical committee and a joint oversight committee will provide advice to both the Executive Committee and the Coordinating Committee. Work in the US will be managed by the MMA Project team as is the case now; work in Europe will be managed by the LSA Project.

The Executive Committee will meet the 2nd and 4th Thursday of each month. Chairmanship of the committee will rotate once per quarter.

There will be an antenna preproposal meeting in Europe, to follow the US one on 18 May.

The Europeans will try to get attendees to our PDR meetings.

The WWW page will evolve toward www.alma.nrao.edu or www.alma.eso.edu as www.alma.xxx is taken.

Payne reported news from Kooi that a 280 K noise temperature had been measured at 4K on a TiN?? SIS structure at 820 GHz.

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Amplitude Calibration at BIMA - Bock

Amplitude calibration hardware was installed behind the sub-reflector of a single antenna at Hat Creek during December, 1998. The associated control hardware and software is complete and integrated into the existing observing systems. The rotating mirror arrangement has proved reliable throughout the winter, during which it was operated regularly during observations. The temperature of the loads was maintained to within a few tenths of a degree. The coupling of the calibration system to the main beam has been measured over a range of wavelengths in the 1mm and 3mm bands. We are presently integrating the calibration hardware with existing data acquisition systems to evaluate its effectiveness in typical observations.

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Progress on BIMA WVR Correlator - Harris

* We have a complete correlator module (16 channels over about 3.5 GHz) ready for testing -- just have to get the analog-to-digital converters to read out properly.

* I've just spent a couple of days visiting David Woody at OVRO (I'm in Pasadena at the moment), where we'll install the first correlator to see what we can learn about hardware, line shapes, try to get some information on altitude distribution, and see if we can improve matters by feeding 16-channel data into his 3-channel system. We expect to bring the correlator and cooled front end together on the telescope in June.

* Johannes and Lee have been making good progress on packaging the software in a flexible way to try double-blind modeling and test phase recovery schemes.

The latter two topics tie directly into investigating the suitablility of the 183 GHz line for the higher site.

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Longest Baseline - Wootten

In my opinion, the longest baseline for which a reasonably cogent scientific case has been made is 10km. The case was partly made in the Tucson science sessions, as it specifically affected the MMA. It was expanded to the 'Atacama Array' when we had the discussions with the Japanese, but I'm not sure that there is any written record of that. In my opinion, the case can be pretty solid for baselines as long as thermal brightness temperatures can be detected on.

Napier talked to Guilloteau, who agrees that he knows of no well-founded reason for baselines in excess of 10km.

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1/f Noise - Wootten

IMHO the basic problem with 1/f is that 1) there are no reliable measurements of it for e.g. an SIS mixer with a HFET amplifier operating at 4-12 GHz. There are rumors that a student of Lyman Page's made a relevant measurement, but I don't know the actual IF he used nor do I know of a memo describing these. Phillips will be changing his receivers to 6 GHz IF and has a postdoc measuring wideband noise. When I spoke to him in December, the noise he was seeing was thought to be dominated by other effects. However, all parties expect this to be a problem for the MMA. Webber agreed in late February at the Euro meeting that NRAO would provide some measurements. There are single beam measurements for HFETs which Marian and Walleck published, for Qband and 3mm; there are the instruments designed for MAP and the GBT which can beat this measured 1/f noise at the added complexity of implementing dual switching beams. Phillips is planning dual beams at CSO at all frequencies. I think that a 'fast enough' OTF map, in which each cell is measured for a time which is small compared to that in which 1/f noise dominates, can be stacked and the noise should end up uncorrelated when these several maps taken in a basket weave or other pattern are added, and that this might be the only way around dual beams. But what is 'fast enough'? For one to be certain of this, one must have a solid theory of total power noise, which brings us to 2) Mark's memo. Mark's memo is the closest thing we have but of course it won't account for systematic noise very well. I think it is our highest priority to get this finished and out. I would like to see it tested also but to my knowledge every NRAO telescope is so dominated by systematics that a confrontation of Mark's ideas with the real world is meaningless. One might be able to do this at the CSO (but they don't really do OTF correctly) or at the JCMT, which Richer has offered to try but right now they don't dump data fast enough.

In the meantime, what to do? The specs in the project book are the best guess as to what the specs on 1/f noise should be so as not to dominate total power performance. I want Mark's memo on total power noise to be finished and issued, followed by a second on 1/f noise. The memo sort of fell by the wayside but let's dust it off and go through it.

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Lowest Frequency - Wootten

Darrell forwarded to me the following email from John:

When discussing very broadband amplifiers for the "30-40" or "30-45" or whatever receiver for the MMA, one should bear in mind that the amplifiers will not have optimum noise temperature and gain over the entire band. Current production receivers using amplifiers based on the MAP design typically perform as follows:

Frequency (GHz) Gain (dB) Noise (K) Input Return Loss (dB)

33 25 not measured -2

36 28 51 -3

40 32 26 -5

43 36 23 -15

45 35 27 -9

48 32 36 -5

50 28 43 -3

The Ka-band amplifiers are excellent at 33 GHz but useless at 43 GHz. (Recall that the waveguide band there is 26.5-40 GHz).

The present design, then, is usable from roughly 36-50 GHz and has optimum performance at the 43 GHz SiO line, but is not at all suited for CMBR/SZ observations near 30 GHz where the atmospheric noise is a minimum. A new design optimized for, say, 33-46 GHz could be made which would have better performance at the low end and probably not much different performance at 43 GHz except for input return loss. However, you can't have everything.

According to Marian, it is possible to build an amplifier with a waveguide bandwidth (26-40 GHz, 30-45.5 GHz, 33-50 GHz, etc) with the noise minimized at any frequency within the band. Traditionally this frequency was the band center but it not need to be. A rule of thumb, stating that the average noise temperature across the band is equal to the minimum noise measured at the highest frequency still should hold. If we chose, for example 30-45 GHz, we would have to use non-standard waveguide components but it could be done. I think we need some more guidance from science requirements.

In my recollection, we discussed this previously and decided that we put a priority on 1) covering the low noise atmospheric region at 30 GHz 2) maintaining overlap with the VLA and VLBA at 40-45 GHz and 3) covering the broadest practical band to allow searches for redshifted CO. These priorities are best addressed, in my opinion, by a receiver operating over 30-45.5 GHz optimized near 33 GHz. This also covers the allocated 31.3-31.8 GHz and 42.5-43.5 GHz bands. The White Paper restricted itself to consideration of narrower bands, hence was more restrictive. I'd like to see the MMA low band cover 30-45.5 GHz if possible.

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Correlator Dumptime - Wootten

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Action Items 8Mar99

UPCOMING REVIEW: On or before 31 May 1999 we review results from the OVRO and BIMA phase correction systems. This will be a telephonic review.

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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Travel

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T. Helfer:

A. Wootten: 12-13 April 43m observing 22-24 April Retreat GB 28 May - 3 Jun AAS 5-10 Jun I99 11 - 13 Jun CSO, 19 - 30 Jun Nagoya Star Formation meeting and Nobeyama

J. Mangum:

M. Yun: 20-28 April Hawaii

B. Butler:

S. Radford: