Introduction, Older Versions of the OSS

This document summarizes the current observational capabilities of the Very Long Baseline Array (VLBA) instrument. It is intended specifically to accompany the Call for Proposals for observing semester 2023B, with a submission deadline of 2022 February 1, but is also the best source for current information on VLBA instrumentation. For capabilities prior to that date, we refer to our overview of previous OSS versions available online.

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 1960's. 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, from widely separated frequencies within the 6-cm band, and 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) in Socorro, New Mexico.

Broad overviews of the range of astronomical research possible with the VLBA are presented in the VLBA 10th anniversary meeting proceedings (Romney & Reid 2005), and the conference proceedings edited by Zensus, Taylor, & Wrobel (1998). Recommended reading for users new to the VLBA includes the "Introduction to the VLBA", "Guide to Proposing for the VLBA", "Guide to Observing with the VLBA", and a short VLBI overview (Walker 1999).

This document's primary intent is to provide, in concise form, the minimal information needed to formulate technically sound proposals requesting VLBA resources. A secondary aim is to describe some of the subtleties of data reduction and telescope scheduling. It is updated synchronously with the VLBA calls for proposals, or more often when required by major changes.

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

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