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 et al. 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 
-
plane coverage; (3) 10 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. The conference proceedings edited by Zensus, Taylor,
& Wrobel (1998), as well as the VLBA 10th anniversary proceedings
(Romney & Reid 2005) provide broad overviews of the kinds of astronomical
research possible with the VLBA. 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. Its secondary aims are to provide information about a few of the subtleties of data reduction and telescope scheduling, lists of relevant software and documentation, plus a list of key NRAO personnel who can be consulted for further, more detailed information. In particular, note that Sections 17 and 18 contain a number of hints and directions about data calibration and imaging. This document, which is updated every 1-2 years, is available through the VLBA astronomer 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, with local assistance at each VLBA antenna site provided by site technicians.