VLA > Introduction

# Introduction

VLA capabilities January 2013 - April 2014

# 1. Purpose of Document

The Observational Status Summary (OSS) summarizes the instrumental status of the Karl G. Jansky Very Large Array (VLA) as of the D-configuration starting January 25, 2013, and should be used when preparing for proposing  for the August 1, 2012 deadline.  For capabilities prior to that date, please consult the previous version of the OSS.

The OSS is intended as a ready reference for those contemplating use of the VLA for their astronomical research. The information is in summary form - those requiring greater detail should consult the VLA's staff members, listed in Key Personnel, or refer to the manuals and documentation listed in Documentation. Most of the information contained here, and much more, is available through the VLA science web pages, and the companion document for the VLBA.

The VLA is a large and complex modern instrument. Some familiarity with the principles and practices of its operation is necessary for efficient use to be made of it.  Although the NRAO strives to make using the VLA as simple as possible, users must be aware that proper selection of observing mode and calibration technique is often crucial to the success of an observing program. Inexperienced and first-time users are encouraged to enlist the assistance of an experienced colleague or NRAO staff member for advice on, or direct participation in, an observing program. Refer to Help for Visitors to the VLA and SOC for details. The VLA is an extremely flexible instrument, and we are always interested in imaginative and innovative ways of using it.

# 2. The Expanded Very Large Array (EVLA) project

The Expanded VLA (EVLA) project is a program to modernize the electronics of the Very Large Array (VLA) that was built in the 1970s and 1980s in order to improve several key observational parameters by an order of magnitude or more.  Some of the details of the EVLA Project may be found on the web, at http://www.aoc.nrao.edu/evla/.   The EVLA project is funded jointly by the US National Science Foundation (NSF), the Canadian National Research Council, and the CONACyT funding agency in Mexico.   Total funding was approximately $94 million in Year 2006 dollars, including$59 million in new NSF funding, $16 million in redistributed effort from the NRAO Operations budget,$17 million for the correlator from Canada, and \$2 million from Mexico.

The EVLA project will be complete on time and on budget at the end of 2012, 11 years after it began.  Its key observational goals are (1) complete frequency coverage from 1 to 50 GHz; (2) continuum sensitivity improvement by up to an order of magnitude (nearly two orders of magnitude in speed) by increasing the bandwidth from the VLA's 100 MHz per polarization to 8 GHz per polarization; and (3) implementation of a new correlator that can process the large bandwidth with a minimum of 16,384 spectral channels per baseline.  A comparison of some of the EVLA performance parameters with those of the original VLA is provided in Table 1.

Note: The "Factor" gives the factor by which the EVLA parameter will be an improvement over the equivalent VLA parameter.

VLA to EVLA transition

The correlator that was the heart of the VLA for three decades was decommissioned on 11 January, 2010, and replaced with the new EVLA "WIDAR" correlator.  The VLA was shut down to outside users until March 2010, during which time hardware was transferred from the old correlator to the EVLA correlator and observing modes commissioned in preparation for EVLA early science. At the same time the direction of the configuration cycles also changed, from ABCDA to DCBAD, in order to facilitate the EVLA correlator commissioning and to limit initial EVLA data rates. The last VLA antenna was retrofitted to EVLA specifications in May 2010.

The first full configuration cycle of early science using the EVLA correlator saw up to 256 MHz of bandwidth offered to the general community, and 2 GHz bandwidth for observers who could be in Socorro to help with EVLA commissioning.  By the end of 2011, at the start of the second configuration cycle, up to 2 GHz bandwidth was offered to the general community.  The full 8 GHz bandwidth is now being offered to the general community at the start of full operations, semester 2013A.

# 3. VLA Science Opportunities

The general capabilities of the Karl G. Jansky Very Large Array (VLA) have been extensively upgraded as stated in the August 1, 2012 call for proposals.   By January 2013, all antennas and receiver bands will be upgraded and extensive testing of the WIDAR correlator will have been done.    The last of the L (1-2 GHz), S (2-4 GHz), X (8-12 GHz) and Ku (12-18 GHz) bands will be installed by late 2012.    Further, the 3-bit sampler system, enabling up to 8 GHz of simultaneous bandwidth at high frequencies, will be installed.

The general capabilities for the 2013A semester (January 25 - April 22, 2013) are extensive with flexible tuning of sub-band spectral line windows using the 8-bit samplers (enabling up to 2 GHz total bandwidth), use of the 3-bit samplers at higher frequencies in a mode that is suitable for wide-band continuum and extragalactic lines and line searches, use of up to 3 independent sub-arrays and a phased array capability for VLBI.

In addition to the general capabilities, NRAO continues to offer shared risk observing options for those who would like to push the capabilities of the VLA beyond those offered for general use.   These are the "Shared Risk Observing" and "Resident Shared Risk Observing" (RSRO) programs.    Another observing program is designed for VLA staff to push the test and validation of enhanced or emerging capabilities of the VLA.    Details of what is being offered for the shared risk programs and what is required to write a proposal for them are available on the web at: https://science.nrao.edu/facilities/evla/early-science/shared-risk-observing-2013a.