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ALMA MEMO #450

Heterogeneous Imaging with the ALMA Compact Array

Melvyn Wright (University of California, Berkeley)

2003/03/21



Keywords: Heterogeneous Imaging, ALMA Compact Array, ACA.

The ALMA Compact Array will be a powerful telescope at sub-millimeter wavelengths for imaging the large scale structures which are not well sampled by ALMA. In this memo, we propose an observing mode for the ACA as a heterogeneous array of 7 and 12 m antennas. We compare three compact configurations: the ACA (12 x 7 m), a heterogeneous ACA with 4 x 12 m antennas, and the most compact ALMA configurations with 60 x 12 m antennas. We present tables of the synthesised beam FWHM, brightness sensitivity and sidelobe levels for source declinations +30, 0 and --30 degrees. Using the ACA as a heterogeneous array with four 12 m antennas doubles the collecting area of the ACA and provides synthesised beams and brightness sensitivities which fill a useful parameter space between the ACA alone and the most compact configurations of the ALMA telescope. Heterogeneous observing provides more short spacings and a good cross calibration of the 7 and 12 m antennas. Calibration of the bandpass and polarization characteristics can be improved by scheduling a few more 12 m antennas for the ACA at times when these calibrations are needed. The location of the ACA in relation to the ALMA array, and the correlator configuration should be considered with these possibilities.


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Last modified: 2003-03-24

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