1. CARMA-23 Heterogeneous Imaging

Pasadena, 13 Dec 2004
  Melvyn Wright
    
A. develop software 

. Primary beam is cross product of voltage patterns for each integration and baseline.

. Errors in the voltage beam pattern of
  the larger antennas which lie within the voltage beam
  pattern of the smaller antennas will corrupt mosaic images.

. Keep the number and parameterization of the primary beam
  models manageable by
  using the same pointing pattern for all antennas at the sample
  interval required for the largest antenna in the sub-array

. Hooks already in Miriad package. 

B. develop array configurations.

. Good uv coverage by locating the SZA array 30m south of the CARMA array.

. Cross correlations between the CARMA and SZA arrays 
  nicely fill the uv plane in the CARMA E configuration.

. Sensitivity is not much changed because the eight 3.5~m
  antennas do not add much collecting area. 

. Sensitivity to large scale structures is improved by sampling shorter uv spacings.

. Density of uv samples is more than doubled which improves the image fidelity.

C. Simulations.

. End-to-end test of software.

. Proof of concept

The heterogeneous 23-antenna CARMA telescope provides some interesting
advantages compared with homogeneous arrays:

1. The different antenna diameters allow a larger range
of spatial frequencies to be sampled by interferometer observations.

2. The different primary beam patterns decouple the source brightness
distribution from the primary beam illumination.

3. The central hole in the $uv$ sampling is smaller which means that
there is less information which depends on single dish observations.

4. There is a large region of overlap in spatial frequencies which can be
used to cross calibrate the single dish and interferometer observations.

5. The heterogeneous interferometer observations provide excellent cross
calibration of the 3.5, 6.1 and 10.4~m antennas.

6. The 3.5~m antennas effectively sample a guard band around the source
brightness distribution, which helps the mosaicing algorithms to define
the extent of the source. These observations of a guard band without
having to make observations at extra pointing centers is an unexpected bonus.

D. Develop correlator.

. 23-antenna.
.  4 GHz bandwidth
. 256 spectral channels.
. 4 polarizations = Full Stokes
. Reconfigurable.
. modular, expandable.
. In use within 3 years.
. leverage commercial and collegiate collaboration.

E. Characterize carma primary beams.

. Measurements of
-  pointing
-  focus.
-  holography

. characterize time scales, stability.

. develop calibration stategy

- Errors from calibration and thermal noise
- periodic calibrations. 


F. Single dish.

. position switching
. OTF spectral line mapping
. Available on all antennas
. can also use for Holography 
. Not continuum.
. Not interferometeric OTF
. Not array receivers.
. Not new Off-line software.