Introduction

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), which was pioneered in the 1960s. The VLBA offers (1) in absentia, year-round station and correlator operation; (2) station locations selected to optimize u-v plane coverage; (3) ten observing bands at wavelengths ranging from 90 cm to 3 mm (two stations are not equipped at 3 mm); (4) rapid, automated selection of receivers and of frequencies within a given receiver; and (5) integrated data flow from acquisition to correlation to post-processing. 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 VLBA is operated remotely from the Pete V. Domenici Science Operations Center (SOC, formerly known as the Array Operations Center) in Socorro, New Mexico.

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 and documentation. It is updated synchronously with the NRAO calls for proposals, or more often when required by major changes.  The current version is available at  https://science.nrao.edu/facilities/vlba/docs/manuals/oss .

Requests for information beyond the scope of this document should be directed to the NRAO Helpdesk.

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The National Radio Astronomy Observatory and Green Bank Observatory are facilities of the U.S. National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Founded in 1956, the NRAO provides state-of-the-art radio telescope facilities for use by the international scientific community. NRAO telescopes are open to all astronomers regardless of institutional or national affiliation. Observing time on NRAO telescopes is available on a competitive basis to qualified scientists after evaluation of research proposals on the basis of scientific merit, the capability of the instruments to do the work, and the availability of the telescope during the requested time. NRAO also provides both formal and informal programs in education and public outreach for teachers, students, the general public, and the media.

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