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The left panels of Figure 2 show the DASI instantaneous uv coverage
and the corresponding synthesized beam in the image plane. Besides
yielding spectral information, the 10 1GHz channels allow frequency
synthesis mapping, since for any given baseline, the corresponding
uv radius varies by 30% over the 10 GHz band, hence the radial
pattern in the uv coverage. The effective snapshot resolution when
all 10 bands are combined is approximately ,
as shown in
the central panel.
Figure 2 also shows the effective sensitivity of the instrument in
lspace. The right panel is an azimuthally collapsed composite of
the lspace window functions for all independent baselines at a
single frequency. Exact antenna spacings on the faceplate were
numerically optimized to yield uniform uv coverage over the angular
range accessible to DASI. Note that the finite aperture introduces
correlations between baselines at neighboring uv points,
particularly between visibilities of the same baseline at neighboring
frequencies.
With the threefold redundancy, the pattern of uv coverage repeats
with each
of rotation. Although the antenna locations repeat
only every ,
the same Fourier components of the sky are
measured under reflection of the array, since the sky is real and its
transform Hermitian.
Figure:
Fourierplane and imaging characteristics of
the DASI instrument. The instantaneous uv coverage of the
interferometer (left), and the resulting synthesized beam (center) for
natural weighting, with approximately
FWHM. (right) The
corresponding lspace coverage at 30 GHz. Note that the threefold
symmetry results in only 26 independent baseline lengths at each
frequency.

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Erik Leitch
20010416