Two years after the 1
Millimeter-VLBI Science Workshop held
at Boston (1996),
it was timely to again bring together the scientists, the users, and the
engineers of the Coordinated Millimeter VLBI Array (CMVA).
The 2 Millimeter-VLBI Science Workshop was held on 27 - 29 May 1999 at IRAM, Granada, Spain. We hope that this second meeting initiates a series of similar future Millimeter VLBI workshops.
For this meeting approximately 50 participants convened from all over the world. The group of astronomers and engineers working in millimeter VLBI is still relatively small, and many of the participants know each other well, although they usually cannot communicate face to face. The workshop gave the opportunity to meet and discuss the progress made during the last years, but also to express wishes and suggestions for further improvements. The contributions presented here illustrate the results of the common effort in mm-VLBI, the scientific progress, and the future possibilities as seen today.
Since 1996, new VLBI experiments were performed at 3mm, 2mm and 1mm. At 3mm, to date up to 12 stations participate in global VLBI sessions, which are organized through the CMVA, and which are performed twice a year. Although sometimes affected by unfavourable weather conditions and technical problems at some sites, these VLBI campaigns are usually successfull and provide good data of compact galactic and extragalactic radio sources. In the continuum, compact active galactic nuclei (AGN) and their jets can be imaged with a dynamic range of up to a few hundred and with resolutions of up to 50 micro-arseconds. This allows detailed studies of the structure and kinematics in the inner-most regions of these radio sources. The reliable mapping of SiO masers and the combination of 3mm data with data obtained at longer wavelengths (7mm) opens promising possibilities for further studies and a comprehensive interpretation of the underlying astrophysical processes.
At the wavelengths of 2mm and 1mm, the number of telescopes is much smaller than at 3mm; the new Heinrich-Hertz telescope on Mount Graham participated in a VLBI experiment at 1mm for the first time. At these wavelengths, small antenna diameters and the presently limited bandwidth allow us to observe only the brightest sources. Therefore, VLBI observations at 2mm and 1mm wavelength are still in an experimental state, and questions of local oscillator, frequency, and clock stability governed the discussions. At 1.3mm, fringes have been obtained already, however only on short continental baselines, and efforts are undertaken to overcome the remaining technical problems of global 1mm VLBI. Here the development of atmospheric phase correction will play an important role. With the addition in the near future of more collecting area (eg. adding Plateau de Bure as phased interferometer in 2001), high angular resolution imaging of continuum sources and spectral line VLBI should become possible soon.
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