The following is a brief account of a meeting between representatives of the LSA project and the MMA project which took place in Charlottesville last week on June 25 and 26th. The European representatives were: Torben Andersen, Roy Booth, Riccardo Giacconi, Michael Grewing, Stephane Guilloteau, Karl Menten, Dietmar Plathner, Peter Shaver, and Francois Viallefond. The US representatives were: Paul Vanden Bout, Bob Brown, Ed Churchwell, Darrel Emerson, Neal Evans, Dave Hogg, Mark Holdaway, Ken Kellermann, Peter Napier, Frazer Owen, Dick Thompson, Juan Uson, John Webber, and Jack Welch.

The purpose of this meeting was to explore a possible collaboration between the two projects. The motivation for a collaboration was to achieve an instrument with capabilities beyond that which either side could achieve alone. Collaboration would also satisfy the NSF's requirement for an international or outside partner for the MMA project and would give the Europeans a stronger position to negotiate for funding and a part of a project that is already much further advanced than the LSA project.

Most of the first day was devoted to discussing the design parameters of the LSA and the MMA. As we already know, the two projects had rather different goals. The LSA design was driven primarily by maximum point source sensitivity and the assumption that it will not operate at submillimeter wavelengths (thus a high site and very accurate pointing are not considered so critical). The MMA workshop, on the other hand, put a very high priority on submillimeter capability (thus a high dry site is essential), which required smaller, precision antennas and stringent pointing accuracy (about 0.1 of the primary beam width at 650 GHz in a 6 m/s wind). The MMA had more emphasis on low surface brightness observations and mosaicing than did the LSA.

The discussion mostly resolved around ways to reconcile these fundamentally different approaches. The Europeans were concerned that we are building a facility with antennae that are too small and will not provide enough collecting area to provide an order of magnitude increase in sensitivity that one should aim for in a major new facility. The Americans were concerned that dishes as large as 15m could not be built to meet the high precision pointing accuracy required for high fidelity mosaicing and tracking even of point sources at submillimeter wavelengths. The Europeans claim that they can build 15m dishes using carbon fiber tubing and aluminum panels for about $3M but they have no pointing error budget for their antennae.

After a day and a half of discussing issues on telescope size, site, imaging, and scientific drivers a resolution was signed by Paul Vanden Bout and Riccardo Giacconi which I copy below in its entirety.

RESOLUTION

Whereas the development of millimeter-wavelength astronomy has shown the potential of large millimeter interferometric arrays for revealing the origin and evolution of stars and planetary systems, of galaxies, and of the universe itself; the communities in the United States and Europe have proposed the construction of the Millimeter Array (MMA) and the Large Southern Array (LSA), respectively; and there is an opportunity through cooperation to achieve more than either community planned; we, as the observatories responsible for these projects and with the support of our communities, resolve to organize a partnership that will explore the union of the LSA and MMA into a single, common project to be located in Chile. Specifically, this partnership will study the technical, logistical, and operational aspects of a joint project. Of particular importance, the two antenna concepts currently under consideration will be studied to identify the best antenna size and design or combination of sizes to address the scientific goals of the two research communities. In doing so we will work through our observatories, utilizing the expertise in millimeter astronomy resident in research groups and institutions in our communities. Finally, we recognize that there are similar goals for millimeter astronomy in Japan, and cooperative activities with that project will continue.

Several working groups were set up at the meeting to study some of the issues. In particular, Frazier Owen (MMA Project Scientist) and (if he accepts) Dennis Downes will chair a small working group (members to be selected by the co-chairs) to compare the the heterogeneous array (our 8-m antennas and their 15-m antennas) and a homogeneous array (all antennas would be 12+/-1 m). The small working group is also charged with getting input from the whole community (e.g., the mailing lists for the various workshops around the world will be used). In addition, there is a working group headed by Peter Napier and and Dietmar Plathner to share technical information and refine numbers and sizes of antennas. The goal is to have an interim report ready by October.

Although there are outstanding unresolved questions, I believe this was a watershed meeting that has opened the way to a possible collaboration that should enhance the probability that the MMA will be funded and that will ultimately provide an array with capabilities well beyond what we could achieve on our own.