CARMA Memo 51.

Antenna Shadowing in the E-Array

Peter J. Teuben and B. Ashley Zauderer (UMD)

We simulated CARMA E-array configuration observations with sources between
declinations of -30 and 85 degrees to determine the extent of shadowing in
this most compact configuration.  The percentage of shadowed visibilities
for various hour angle ranges at each source declination is presented.
We find that shadowing only becomes significant for a standard four-hour
track, centered on transit, for sources below a declination of 0 degrees.
The shadowing ramps up for larger hour angles, especially for lower
declination sources.  The percentage of shadowed visibilities we obtained
uses the full antenna diameters, when in practice, one might be able to
get better performance from the actual system by including visibility data
where the antenna dish was only slightly shadowed at the edge of the dish.
We suggest the use of MIRIAD task, csflag, to flag shadowed antennas.
However, users should be aware that shadowing does not seem to have
a detrimental effect on the data, as unflagged shadowed data have not
shown a drop in amplitude or scattering in phase coherence, as might have
been expected.  Shadowing is not a serious concern in the less compact
configurations:  A, B, C and D, although users may still want to run
csflag to see the extent of shadowing themselves and to compare their
maps with and without this data.