This document summarizes the current observational capabilities of NRAO's Very Long Baseline Array (VLBA). The VLBA is an array of 10 25-m diameter antennas distributed over United States territory (Napier 1994, Napier 1995). It is the first astronomical array dedicated to observing by the method of Very Long Baseline Interferometry (VLBI), pioneered in the 1960s. The VLBA offers (1) in absentia, year-round antenna and correlator operation; (2) antenna locations selected to optimize u-v plane coverage; (3) 9 receivers in the range 90 cm to 7 mm at each antenna; (4) quick computer control of receiver selection (receiver agility) and of frequency selection for a given receiver (frequency agility); and (5) smooth integration of data flow from the acquisition to the processing to the post-processing stages. VLBA observations conducted in VLBA (Romney 1990) and Mark III (Rogers 1983) data formats can acquire simultaneous dual circular polarizations from any single receiver or from the 13/4 cm receiver pair.
This document's primary intent is to provide, in concise form, the minimal information needed to formulate technically sound proposals for observing time on VLBA antennas. Its secondary aim is to provide resource lists of relevant software and documentation, plus key NRAO personnel who can be consulted for further, more detailed information. This document, which will be updated regularly, is available via either anonymous FTP as a PostScript file with name ``obssum.vlba.ps'' in directory ``pub'' on host ``ftp.aoc.nrao.edu'' (146.88.1.103), or from the VLBA home page via a WWW browser (see Section 26.3). If you want a paper copy of this document, then request one from Lori Appel (see Section 26.4). Updates of this document will be announced via the NRAO VLBI e-mail exploder and the NRAO Newsletter. Anyone wanting to be added to this exploder should send an appropriate mail message to ``vlbi-request@nrao.edu''. If you want to subscribe to the NRAO Newsletter, contact Joanne Nance in Charlottesville (jnance@nrao.edu, telephone +1-804-296-0323).
Where possible, the symbols used in this document are the same as those in Synthesis Imaging in Radio Astronomy, 1989, edited by R.A. Perley, F.R. Schwab, & A.H. Bridle, published as Volume 6 of the Astronomical Society of the Pacific Conference Series. However, the present document introduces some new symbols as well.
The VLBA is operated remotely from the Array Operations Center (AOC) in Socorro, New Mexico, with local assistance at each VLBA antenna site provided by site technicians.