The collecting area, receiver suite, and geographical location of the NRAO Very Large Array (VLA) make it a valuable addition to a VLBI array. The VLA supports standard VLBI observations at frequencies of 0.33, 1.7, 5.0, 8.4, 15, 22, and 43 GHz. The VLA can be used either as a single antenna or as a phased array. In the latter observing mode it offers the equivalent sensitivity, including sampling losses, of a single 115-m antenna. The VLA has a VLBA data acquisition system for writing on instrumentation tapes in VLBA or Mark 3 formats and a hydrogen-maser frequency and time standard. The VLA participates in VLBI programs run during Network sessions, as well as in non-Network VLBA programs run outside of Network sessions. Its participation in either type of program is arranged by the VLA/VLBA scheduler Barry Clark (see Section 17).
If the VLA is used in phased-array mode along with the 10 antennas of the VLBA, then there can be significant improvements in both baseline and image sensitivity. Assuming that an individual VLA antenna has the same system-equivalent-flux-density as a VLBA antenna and that all 27 VLA antennas are well phased, then baselines between the phased array and any VLBA antenna should be about 4.6 times more sensitive than baselines between any two VLBA antennas. Also, if the 45 baselines among VLBA antennas are augmented by 10 more baselines between the phased array and each VLBA antenna, then the sensitivity improvement in a naturally-weighted image should be a factor of about 2.4.
Sections 1 through 12 of this guide contain the essential information needed by users conducting standard VLBI observations at the VLA. Subsequent sections offer further detailed information useful to VLA and VLBA Operations, to visitors and NRAO staff wanting to interact with the VLBI hardware at the VLA, and to users planning nonstandard VLBI observations at the VLA.
Documents complementary to this guide include the ``VLA Observational Status Summary'' by G.B. Taylor, J.S. Ulvestad, & R.A. Perley; the ``VLBA Observational Status Summary'' by J.M. Wrobel; ``The SCHED User Manual'' by R.C. Walker; ``A Step-by-Step Recipe for VLBA Data Calibration in AIPS'' by J.S. Ulvestad; and ``The VLA Calibrator Manual'' by R.A. Perley & G.B. Taylor. These documents and this guide are available on the Web through the VLA astronomer's page or the VLBA astronomer's page, both of which can be accessed through the NRAO home page at http://www.nrao.edu.