Image Fidelity as a Function of Source Size and Calibration Errors.

Melvyn C. H.  Wright
Radio Astronomy Laboratory, University of California, Berkeley


In this memo we simulate observations with the CARMA telescope and
calculate the image fidelity as a function of source size, pointing and
calibration errors. We explore the effects of calibration errors
on incorporating single dish data with interferometer observations.
These results can be used in planning observations with the CARMA telescope.

We simulated observations using an image of Cas A scaled to
different diameters as a source model.  Simulated uv data sampled by
the heterogeneous array of 10.4, 6.1, and 3.5~m antennas were used to
make images at 230 GHz.

The different antenna diameters and primary beam sizes allow sources
up to ~ 32'' diameter to be observed with a single pointing center
using the 15-antenna D-configuration at 230 GHz. Because of the different
primary beam sizes, the data must be treated as a mosaic observation.
The image fidelity decreases as the source size increases.  Sources up to
~ 64'' diameter can be observed with a 7-pointing hexagonal mosaic
using the 15-antenna D-configuration at 230 GHz.

The image fidelity decreases when calibration errors are
introduced.  If calibration errors are small, (1%), then a joint
deconvolution gives the best image fidelity.  The image fidelity is very
dependent on high quality single dish data.  For amplitude
fluctuations greater than ~ 5% the best image fidelity is obtained
using MOSMEM with a default single dish image rather than the joint
deconvolution which gives more weight to the single dish data

The  fidelity is greatly improved by mosaicing with the 23-antenna DZ
configuration. The short interferometer
spacings obtained with the 3.5m antennas provide much more robust
information on the large scale structure and cross calibrate the single
dish and interferometer observations.