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A. Greve, B. LeFloch, J. Peñalver (IRAM)
Abstract: Radio astronomical observations at millimeter wavelengths
with Cassegrain telescopes often use on-source off-source measurements with a
wobbling subreflector to eliminate the influence of the Earth's atmosphere.
The tilt of the subreflector produces the required beam throw, but also a
coma-like wavefront deformation noticeable as a degradation of the beam
pattern and a reduction of the main beam power. We demonstrate with
measurements, made with the IRAM 30-m telescope at 1.3 mm wavelength
(230 GHz) of the quasi point-like source Mars and the extended source Saturn,
that it is possible to eliminate to large extent this wavefront deformation
when using a near-focus corrector, in this telescope conveniently located on
the co-rotating Nasmyth mirror.