This document summarizes the current observational capabilities
of NRAO's Very Long Baseline Array (VLBA) instrument. The VLBA is an
array of ten 25-m diameter antennas at stations distributed over United
States territory (Napier et al. 1994; Napier 1995). It is the first
astronomical array dedicated to observations using the technique of
Very Long Baseline Interferometry (VLBI), pioneered in the 1960s. The
VLBA offers (1) in absentia, year-round antenna and correlator
operation; (2) station locations selected to optimize 
-
plane
coverage; (3) ten receivers in the range 90 cm to 3 mm at each antenna
(two antennas not equipped at 3 mm); (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 can acquire simultaneous dual circular
polarizations from any single receiver or from receiver pairs at 13/4
cm or 90/50 cm. Broad overviews of the kinds of astronomical
research possible with the VLBA are presented in the conference proceedings
edited by Zensus, Taylor, & Wrobel (1998), and the VLBA 10th anniversary
proceedings (Romney & Reid 2005). Recommended reading for users new to
the VLBA includes a short VLBI overview (Walker 1999b) and a short
guide for novice users of the VLBA (Ulvestad 2004).
This document's primary intent is to provide, in concise form, the minimal information needed to formulate technically sound proposals requesting VLBA resources. Secondary aims are to describe some of the subtleties of data reduction and telescope scheduling, and to list relevant software, documentation, and key NRAO personnel who can be consulted for further, more detailed information. It is updated synchronously with the NRAO calls for proposals, or more often when required by major changes, and is available through the VLBA Information for Astronomers page at http://www.vlba.nrao.edu/astro/ .
The VLBA is operated remotely from the Pete V. Domenici Science Operations Center (DSOC, formerly known as the AOC) in Socorro, New Mexico.