ALMA Memo #283

Observing Efficiency of a Strawperson Zoom Array

Keywords: array, zoom, configuration, sensitivity, resolution, tapering

We compare the observing efficiencies of variable resolution zoom arrays to conventional fixed array designs. To investigate this question in detail we analyse a specific strawperson zoom array. This strawperson array follows a logarithmic three-armed spiral on intermediate scales (radius 100m - 1500m) but smoothly interfaces to a ring and a dense pack for the largest and smallest configurations respectively. Three telescopes are moved twice a week; using such a design it is feasible to have two full cycles per year through the 3km configurations.

We find that slightly fewer baseline-hours are lost to reconfiguration and calibration using zoom rather than fixed array designs. However, a much more significant advantage of zoom arrays is the ability to largely avoid data tapering in making images which require specific resolutions. A large fraction of ALMA observations which demand inter-comparisons of different line transitions or with optical and IR images will be of this type. We estimate that by avoiding tapering zoom arrays can observe approximately twice as many such sensitivity-limited fixed-resolution projects per year. We make a first attempt to consider the impact on zoom arrays of practical constraints such as wind delays on reconfiguration and fluctuations of demand. It appears that these do not effect the fundamental conclusions that zoom arrays can have higher efficiency than fixed arrays for a slightly lower construction and operating cost.

From here, you can:

View a PDF version of ALMA Memo #283.

Download a 0.54 MB gzipped postscript version of ALMA Memo #283 from

here

Last modified: January 05, 2000