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Expanded Very Large Array

Link to EVLA Web site and link to VLA web site.

I. General project/facility description

  1. Overview of the facility/project
    The Very Large Array (VLA) is an aperture synthesis array of radio antennas located on the Plains of San Augustin, at 2100 meters elevation, 80 km west of Socorro, New Mexico. Its properties are being changed substantially leading to a vastly superior instrument dubbed the Expanded VLA (EVLA).

    The VLA consists of twenty-seven 25 meter antennas arranged in a wye ("Y") configuration, with nine antennas on each 20 km arm of the wye. (There are 27 antennas on the array at a given time, with a 28th antenna being cycled through the antenna assembly building for major maintenance.) The antennas are transportable along a double rail track, and may be positioned at any of 72 possible stations by either of the two specially designed antenna transporters. In practice, the antennas are rotated among four standard configurations, which provide maximum baselines of 1, 3, 11, and 36 km ( D, C, B, and A configurations, respectively). Additional "hybrid" configurations with a long northern arm are used to provide optimal sampling of sources in the south. The ability to reconfigure the antenna locations provides the VLA with variable resolution at fixed frequency or fixed resolution at variable frequency. A complete cycle of all the configurations takes place every 16 months. Thus the different array configurations are out of phase with the annual weather cycles, so that the prime winter observing conditions cycle among the configurations over a four-year period.

  2. Managing institution and organization
    The VLA is a facility of the National Radio Astronomy Observatory, managed by Associated Universities Inc. under a cooperative agreement with the National Science Foundation. NRAO is a federally funded research and development center (FFRDC), while AUI is a non-profit university-based consortium. The VLA is managed directly from the Array Operations Center (AOC) in Socorro, NM, while NRAO is headquartered in Charlottesville, VA. AUI offices are located in Washington, DC.

  3. Funding source(s)
    The VLA currently is funded entirely by the National Science Foundation, through the NRAO Operations budget, which always has funded the entire cost of astronomical operations. Some capital improvements have been funded by external means. In the late 1980s, VLA funding was enhanced significantly by NASA, in order to support telemetry return from Voyager 2 at Neptune. The total funding received was approximately $7 million in dollars-of-year. This funded the 8.4 GHz receiving systems and essential infrastructure maintenance, such as the supply of diesel generators and the repair of the VLA power-distribution system. In the 1990s, the beginning of the installation of 43 GHz receivers was funded by UNAM, in Mexico, while part of the completion in the early years of the new century was funded by the Max Planck Institut fuer Radioastronomie. Small grants from the NSF Major Research Instrumentation program also were used for 43 GHz, as well as for the fiber-optic link to the VLBA Pie Town antenna. The total external funding for 43 GHz was about $2 million, while the total for the Pie Town link was $0.7 million, including $0.2 million contributed by AUI. The Naval Research Laboratory funded most of the 74 MHz observing systems.

  4. Construction history and cost
    The VLA was recommended as the Number 1 priority for new projects in the decade of the 1970s, by the 1970 Astronomy Survey Committee ("Greenstein Committee"). The original VLA proposal was submitted to the National Science Foundation in 1967. NSF submitted the proposal for construction to Congress in 1971; Congress authorized the VLA program and provided initial funding in 1972. Construction was concluded in 1980, a year ahead of the original schedule, and the VLA was dedicated in October 1980. The initial cost estimate in March 1971 was $76 million in dollars-of-year, and the final construction cost was $78.6 million, in the same units (during an era when inflation often topped 10%).

    The VLA began operation with four major receiving bands. Additional ones were added in the interim: the 8.4 GHz system in 1988, 327 MHz in 1989, 74 MHz in 1998 and 43 GHz in 2003. Additionally a fiber-optic link to the VLBA telescope in Pie Town, New Mexico in 1998 has doubled the maximum resolution of the VLA; this link is critical to ~15% of the A configuration observing programs.

    The EVLA is an on-going project designed to increase significantly the VLA's technical capabilities. It is described, appropriately, under future capabilities below.

  5. Operational history and cost
    VLA operations costs are dominated by maintaining the telescope and site infrastructure, as well as actual operation of the telescopes. Direct VLA Operations costs in FY05 are $6.95M.

    VLA Operations and VLBA Operations take place within common technical divisions of NRAO's New Mexico (VLA/VLBA) Operations, as does EVLA development. Costs are reduced by sharing of personnel with the VLBA for the operations and development projects. A number of other activities are shared for all of NRAO and not included in the direct budget; these include, for example, human resources, fiscal and purchasing, library services, postdoc and student programs, tenured scientific staff, Education and Public Outreach, and the Central Development Laboratory. NRAO has not established a formal means of charging internal overhead ("indirect") costs for these centralized functions, but the best estimate is that NRAO-wide support of each operating telescope or project requires about $3M in indirect costs. Using this estimate, the indirect costs of $3M are an additional 43% on top of the direct costs of $6.95M, and the total cost of operating the VLA in FY05 will be approximately $9.95M.

    After completion of the EVLA, significant additional funds will not be required for its operation; the VLA will become the EVLA, with approximately the same operational staffing level as in previous years.

II. Technical details

  1. Specifics of telescope/instrument
    The VLA operates with receiving systems at 8 different bands:

    Frequency Range
    0.073 to 0.074524.0
    0.305 to 0.3376.0
    1.24 to 1.701.4
    4.50 to 5.000.4
    8.08 to 8.750.24
    14.65 to 15.3250.14
    21.2 to 25.20.08
    40.5 to 44.50.05

    At its most sensitive bands of 1.4, 5, and 8 GHz, the VLA can achieve an r.m.s. noise level of 50 microJy per beam in a 10-minute continuum observation. In some bands, the VLA can be used well outside the cited range, with a corresponding loss in sensitivity. For instance, CO at a redshift of 6.4 has been observed at 46 GHz, outside the highest sensitivity region of the 43 GHz band.

    The current VLA correlator has quite limited capability, providing (for example) as few as 8 spectral channels for each of four intermediate-frequency (IF) channels at 25-MHz total bandwidth, and up to 512 channels for single IFs from 195 kHz to 1.56 MHz total bandwidth. It will be replaced by the much more capable EVLA correlator in 2008-2009.

  2. New capabilities anticipated/planned in next 5-10 years
    A VLA Upgrade was recommended by the 1990 Astronomy and Astrophysics Survey Committee (the "Bahcall committee") report, in recognition of the high scientific productivity of the VLA and the fact that its electronic technology was becoming obsolete at a rapid pace. The 2000 decade committee, known as the McKee-Taylor committee, recommended a related VLA Expansion (or EVLA Project) as its 2nd highest priority ground-based astronomy project for the 2000-2010 decade. The EVLA has been divided into two parts for administrative and funding purposes.

    Some of the capabilities of the current VLA, EVLA (after Phase I) and EVLA (after Phase II) are summarized in this table.

    # baselines351351666
    Angular resolution at 5 GHz0.4"0.4"0.04"
    Frequency coverage as percent of
    total 1-50 GHz band
    Maximum bandwidth per polarization0.1 GHz8 GHz8 GHz
    # freq. channels at max bandwidth161638416384
    Max # channels51241943044194304
    Highest freq resolution381 Hz0.12 Hz0.12 Hz

III. User profile

  1. % of "open skies" time
    The VLA presently operates with 100% of its scientific observing time allocated in an open-skies, peer-reviewed mode.

    In addition regular programs, "large" proposals, which request time allocations on the order of 300 hours or more per year, are solicited once per 16-month configuration cycle. These are subject to review by a special Large Proposal Review Committee, consisting entirely of scientists from outside NRAO. Currently about 15 - 20% of total VLA observing time is allocated to these projects.

  2. Institutional affiliations of users
    According to the NRAO Observing Summary for 2003, 847 individual astronomers from 205 institutions used the VLA for scientific programs. Eighty-eight of these institutions, or 43% (same percentage as the VLBA), are located in the U.S. Typically, 50%-65% of the PIs of VLA proposals are from the U.S., and the remainder from foreign countries. About 75% of all VLA proposals contain at least one U.S. investigator. Counting all accepted proposals that received observing time during 2003, there were a total of 847 observers, including 801 users from outside NRAO, 35 permanent NRAO staff and 11 NRAO postdocs.

  3. Student access, involvement, usage
    Out of the 847 observers using the VLA in 2003, 86 were students. Those students at U.S. institutions are provided travel and housing support if they wish to visit Socorro to observe or to analyze their VLA data. In the NRAO summer student program during 2004, seven students in Socorro and Charlottesville did projects involving VLA observing and data reduction, while two more studied imaging and data-reduction techniques related to the EVLA. Four of these nine students were in the NSF Research Experiences for Undergraduates (REU) program, while the other five were funded by NRAO in its Graduate Research Program. In addition, the 11 summer students in New Mexico were granted VLA time to make an observation as a class project. In the 2000 program, this summer-student observation resulted in the first detection of radio emission from a brown dwarf, and a subsequent Nature paper. Although there is no complete list at present, at least 200 Ph.D. dissertations have been completed using the VLA.

IV. Science Overview

  1. Current forefront scientific programs

  2. Major discoveries (through 1999)

  3. Science highlights of last 5 years

  4. Main future science questions to be addressed
    Current VLA:



  5. Synergies with other major forefront facilities
    As the most powerful and productive radio telescope in existence, the VLA provides the radio complement to many investigations that seek radio data in conjunction with other instruments. A few examples include:

  6. Unique contributions
    The VLA has 27 antennas, providing outstanding aperture plane coverage, with wide frequency coverage, long baselines, and two-dimensional sampling of the aperture plane. Other notable general purpose aperture synthesis arrays operating at centimeter wavelengths are the Westerbork Synthesis Radio Telescope, the Australia Telescope Compact Array (ATCA), and the Multi-Element Radio-Linked Interferometer Network (MERLIN), all of which have many fewer baselines than the VLA. The international desire to use the VLA, as shown by the proposal pressure, provides clear evidence of its unique capabilities.

    These outstanding characteristics will be amplified many times when the EVLA is completed.

V. Education/Outreach activities

The VLA is the central core of an outreach program that generally incorporates both the VLA and VLBA. VLA activities generally include the VLBA as some component. For example, there are VLBA displays in the VLA Visitor Center.

  1. Visitor facility
    A 2400 sq ft Visitor Center, built in 1983, is located at the VLA site with 900 sq ft of exhibit space. A 400 sq ft gift shop was added in 2003. It provides revenue to pay a gift shop clerk to be on hand to answer questions. Some exhibits are updated every few months, spotlighting the work teams at the VLA and VLBA. Open houses for the general public take place twice per year, coinciding with the opening of the nearby Trinity site (location of the first atomic bomb test) to take advantage of the increased tourist traffic. In 2004 these events served 524 people, with tour groups led by a variety of VLA and VLBA scientific and technical staff. During the summer months, our summer students also give VLA guided tours to the general public on the weekends.

    Guided tours for education and astronomy groups take place at the VLA throughout the year. During 2004, 65 pre-arranged tours were given to 2020 people. Sample tour groups included elementary-school classes, Festival of the Cranes attendees, graduate students, and teachers. The VLBA site technicians also give tours and public presentations upon request and as time allows. In 2004, we had 24,000 visitors to the VLA Visitor Center, and 1000 visitors to the VLBA sites. Funding sources for the EPO programs include the NRAO Operations budget (which pays the education officer), the Visitor Center gift shop (which pays the gift shop staff), plus small grants from the NSF Research Experience for Teachers (RET) program and the NASA IDEAs program.

  2. Student programs
    See the summary of all student programs at NRAO, including the VLA.

    The VLA and VLBA staff participate in many activities throughout the year in the local school districts, ranging from giving lectures, to mentoring science fair projects, to judging in science fairs. NRAO also employs undergraduate engineering and computer science students in its co-op program.

  3. Other (as apply)
    Every other year, NRAO conducts the Synthesis Imaging Summer School, an 8-day school at which attendees are taught the basics of radio interferometry, as well as specialized techniques relating to both VLBI and connected element interferometers, including applications and tutorials for VLBA, VLA, and ALMA. The 9th such school was held in 2004, and had 148 attendees. Typically, about 60% to 70% of the attendees are undergraduate or graduate students, and another 15% are postdoctoral research associates. The workshop also produces a book based on the lecture notes which is used as the text in many courses.

    NRAO staff have also been involved in many other activities such as the "Enchanted Skies Star Party", a 2-week "Radio Astronomy for Teachers" course and a Chautauqua short course, "Interferometry in Radio Astronomy". Travel support is provided for U.S. observers using the VLA, and page-charge support is provided for their subsequent publications.

    NRAO has a regular program of press releases and other press information, including regular press conferences that feature NRAO results at the semi-annual American Astronomical Society meetings. Typically, there are a half-dozen releases per year featuring VLA results. from astronomers throughout the U.S. and around the world. The NRAO press releases may be found at

VI. Documentation/website URLs

  1. URL of facility website for the EVLA for the VLA

  2. URL of EPO website or for general NRAO programs.
    Most of the "Useful Links" from the facility website are oriented to the general public, including information about tours, shopping, frequently asked questions, and highlights of current observations.

  3. URL(s) of any brief overviews of project/facility

  4. URL(s) of miscellaneous documentation
    Information for users, proposers, and other astronomers may be found via the "Astronomers" link under the main facility website, at The most complete technical description of the VLA is located at; this "Observational Status Summary" is updated approximately annually. A global document entitled "What Does NRAO Offer You," including a description of visitor programs and benefits (e.g., page charge and travel support) may be found at

This page created and maintained for the RMSPG by Martha Haynes Last modified: Fri Feb 11 07:00:00 MST 2005 by Jim Ulvestad