The 74MHz System on the Very Large Array

Details The 74MHz System on the Very Large Array The 74MHz System on the Very Large Array

2007-04-23

arxiv.org/abs/0704.3088v1

Astronomy and Astrophysics

Astrophysics

73 pages, 46 jpeg figures, to appear in ApJS

Scientific paper

10.1086/519022

The Naval Research Laboratory and the National Radio Astronomy Observatory completed implementation of a low frequency capability on the VLA at 73.8 MHz in 1998. This frequency band offers unprecedented sensitivity (~25 mJy/beam) and resolution (~25 arcsec) for low-frequency observations. We review the hardware, the calibration and imaging strategies, comparing them to those at higher frequencies, including aspects of interference excision and wide-field imaging. Ionospheric phase fluctuations pose the major difficulty in calibrating the array. Over restricted fields of view or at times of extremely quiescent ionospheric ``weather'', an angle-invariant calibration strategy can be used. In this approach a single phase correction is devised for each antenna, typically via self-calibration. Over larger fields of view or at times of more normal ionospheric ``weather'' when the ionospheric isoplanatic patch size is smaller than the field of view, we adopt a field-based strategy in which the phase correction depends upon location within the field of view. This second calibration strategy was implemented by modeling the ionosphere above the array using Zernike polynomials. Images of 3C sources of moderate strength are provided as examples of routine, angle-invariant calibration and imaging. Flux density measurements indicate that the 74 MHz flux scale at the VLA is stable to a few percent, and tied to the Baars et al. value of Cygnus A at the 5 percent level. We also present an example of a wide-field image, devoid of bright objects and containing hundreds of weaker sources, constructed from the field-based calibration. We close with a summary of lessons the 74 MHz system offers as a model for new and developing low-frequency telescopes. (Abridged)

Affiliated with

Also associated with

No associations

Rating

The 74MHz System on the Very Large Array does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with The 74MHz System on the Very Large Array, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The 74MHz System on the Very Large Array will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-224977