Primary Goals for the

Ongoing development of the upgrade concept has demonstrated that improvements of a factor of ten or more over current capabilities are achievable in all four key areas. We define the following as primary performance goals of the :

• Sensitivity The current sensitivity limit (the expected rms in an image made with 12 hours' data, natural weighting, all available antennas, and the maximum available bandwidth) for the VLA is approximately 6  at the most sensitive bands - 1.4 GHz, 4.9 GHz, and 8.4 GHz. Improvements in bandwidth, receiver design, and antenna efficiency can greatly improve the sensitivity at all bands, especially at the higher frequencies. At the lower frequencies, the sensitivity limit is reached in practice only over a limited area of the primary beam at high angular resolution, because of the effects of bandwidth smearing; an upgraded correlator can relieve this restriction. We therefore define as a goal:

  

  The means by which this sensitivity will be obtained will also give significant improvement at other frequencies - typically by a factor of five at frequencies below 2 GHz, and a factor of ten to thirty for the 40 to 50 GHz band. Improved sensitivity also brings improved calibration (and self-calibration) quality because the averaging time needed to reach given phase and amplitude noise is reduced, and because more (weaker) sources can be used for phase-referencing.
• Frequency Coverage The current VLA has very limited frequency coverage - targeting only the major centimeter-wavelength spectral lines (, OH, , ) and selected narrow continuum bands. Many considerations, based both on continuum and spectral line observing, now argue for a much expanded frequency tunability. We therefore define as a goal:

  

  This frequency range is that which can be accessed from the Cassegrain secondary focus ring. We would like to obtain similar frequency availability at lower frequencies as well, although not at the cost of diminishing the array's capabilities at higher frequencies. We thus define a secondary goal:

  

  which must be accomplished from the prime focus.
• Spectral Line Resolution, Bandwidth, and Flexibility The current correlator severely restricts the science from the VLA. A modern correlator is critically needed to keep pace with the array's current, and future observing capabilities. A primary goal is:

  

  but note that these are not all required simultaneously.
• Angular Resolution The detailed the broad-based scientific benefits from increasing the VLA's resolution. Because the objects we wish to observe are complex, it is not sufficient to add a sparse sampling of intermediate-length baselines. To maximize the scientific return, we define as a goal:

  

These improvements would make a ``new VLA" that would continue to set the world standard for radio astronomical imaging from meter wavelengths to long millimeter wavelengths for another generation.