AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 62. High Angular Resolution Science with the NRAO Very Long Baseline Array
Topical, Oral, Wednesday, June 2, 1999, 8:30-10:00am, 10:45am-12:30pm, 2:00-3:30pm, 3:45-5:30pm, International Ballroom South

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[62.01] Capabilities of the Very Long Baseline Array

J.S. Ulvestad (NRAO)

The Very Long Baseline Array (VLBA), dedicated in 1993, is the world's first radio-telescope array dedicated to Very Long Baseline Interferometry (VLBI). It consists of 10 identical 25-meter radio telescopes spread across the U.S. and its territories, from the U.S. Virgin Islands to Hawaii. Baseline lengths ranging from 200 to 8000 km provide sensitivity to a wide variety of structures in compact radio sources. All telescopes operate in nine frequency bands, from 0.3 to 43 GHz (7 mm to 90 cm wavelength), and some are instrumented at 86 GHz as well; the maximum resolution thus approaches 100 microarcseconds, several hundred times finer than the best resolution of the Hubble Space Telescope. The telescopes can switch frequencies in seconds, and also are capable of simultaneous observations at 2.3 and 8.4 GHz for geodesy and astrometry. Cooled receivers are employed, with typical system temperatures in the range of 30--40 K at centimeter wavelengths.

The dedicated nature of the VLBA, and the identical telescopes, have made routine a number of types of observations that were not possible with previous VLBI arrays. In particular, VLBI polarimetry is straightforward, and nearly half the observations use the phase-referencing technique (analogous to the normal phase calibration of the VLA), enabling routine imaging of millijansky-strength sources. New capabilities such as automatic allocation of recording tapes, and hands-off transfer of VLBA calibration data, make observing with the VLBA nearly as simple as the VLA, which has been used for 20 years by astronomers with a wide variety of specialties. This paper introduces the capabilities and user-friendliness of the VLBA, and will be followed by a series of talks (many by students and non-experts) that describe some of the early science results obtained with the VLBA.

The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

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