PROCEEDINGS ARTICLE | September 28, 2004
Proc. SPIE. 5489, Ground-based Telescopes
KEYWORDS: Observatories, Calibration, Image resolution, Distortion, Antennas, Spatial resolution, Algorithm development, Electromagnetic coupling, Galactic astronomy, Radio astronomy
The 74 MHz system on the National Radio Astronomy Observatory's Very
Large Array (VLA) has opened a high-resolution, high-sensitivity
window on the electromagnetic spectrum at low frequencies. It
provides us with a unique glimpse into both the possibilities and
challenges of planned low-frequency radio interferometers such as
LOFAR, the LWA, and the SKA. Observations of bright, resolved radio
sources at 74 MHz provide new scientific insights into the structure,
history, and energy balances of these systems. However many of these
scientifically motivated observations will also be critical to testing
the scientific fidelity of new instruments, by providing a set of
well-known standard sources. We are also using the 74 MHz system to
conduct a sky survey, called the VLA Low-frequency Sky Survey (VLSS).
When complete it will cover the entire sky above -30 degrees
declination, at a 5σ sensitivity of 0.5 Jy/bm-1, and a resolution of 80" (B-configuration). Among its various uses, this
survey will provide an initial grid of calibrator sources at low
frequency. Finally, practical experience with calibration and data
reduction at 74 MHz has helped to direct and shape our understanding
of the design needs of future instruments. In particular, we have
begun experimenting with angle-variant calibration techniques which
are essential to properly calibrate the wide field of view at low
frequencies.
