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Very Large Array 2010 Initiatives

by Heidi Medlin last modified Apr 25, 2011 by Pat Murphy

Very Large Array 2010 Initiatives:
An Optimized Enhancement Program

Currently on time and on budget for completion at the end of FY2012, the first phase of the Expanded Very Large Array Project (EVLA) will offer the astronomical community an order of magnitude increase in sensitivity above the original VLA, contiguous frequency coverage between 1 and 50 GHz, and incomparable flexibility in the set up of the new WIDAR correlator.

We propose a trio of relatively low-cost (< $12M total cost, FY09 dollars) enhancements to the EVLA:

  • (i) Adding 20 new pads for existing EVLA antennas to provide an ultra-compact array configuration that will offer enhanced speed and surface brightness sensitivity, improved sidelobe response, greatly improved image fidelity (by a factor of 7), as well as improved mosaicing. Scientific applications of these new capabilities will include large-angle low-surface brightness surveys and mosaic observations of large sources, ideally carried out in conjunction with the GBT and other large, single-dish antennas, imaging of the Sunyaev-Zeldovich cosmic microwave background decrement in galaxy clusters, HI and non-thermal imaging of nearby galaxies, the imaging of Galactic chimneys and shell structures, maps of Zeeman splitting of HI, molecular, and recombination lines, the imaging of comet emission, and the imaging of diffuse synchrotron emission from particle acceleration sites throughout the universe.

    Supplementary Materials:

  • (ii) A low-frequency improvement program that will replace the VLA's "legacy" 327 MHz and 74 MHz receiver systems with modern systems having lower noise, wider instantaneous bandwidth, and improved feeds. The proposed upgrade would especially enhance the capabilities of EVLA's unique long baseline configurations, and would offer enormously improved scientific access to studies of cosmic reionization, radio relics and halos, the lifecycle of AGNs, continuum and spectroscopic observations of high-redshift sources, free-free and synchrotron-self absorption, as well as Faraday rotation, scattering and interstellar medium studies in the Milky Way and other galaxies.

    Supplementary Materials:

  • (iii) Adding a suite of compact water vapor radiometers (WVRs) to the EVLA to improve the array's phase stability at frequencies above 8 GHz by correcting for rapid tropospheric phase errors produced by water vapor fluctuations. Based on a proven prototype design, these devices will use measured fluctuations in the brightness temperature of the 22 GHz atmospheric water line to derive short-term phase corrections that will improve the quality of observations (especially those on longer baselines), increase observing efficiency at high frequencies, and greatly reduce seasonal constraints on array usage.

    Supplementary Materials:

Each of these enhancements will greatly increase the scientific reach of the EVLA, has extremely low technical risk, and will strongly leverage the US astronomical community's ongoing and long-standing investment in this unique instrument.

Note that there is also a proposal for a more ambitious bridge to a next-generation high-frequency array. The North American Array concept is being submitted by the NRAO New Initiatives Office in partnership with institutions across the astronomical community.

See also the NRAO Astro2010 Page for more on what NRAO is submitting to the review panel(s).