COMA CORRECTION OF A WOBBLING SUBREFLECTOR

Radio astronomical observations at millimeter wavelengths with Cassegr ain telescopes often use on-source/off-source measurements with a wobb ling subreflector to eliminate the influence of the Earth's atmosphere . The tilt of the subreflector produces the required beam throw, but a lso a coma-like wavefront deformation noticeable as a degradation of t he beam patient and a reduction of the main beam power. We demonstrate , with measurement made with the IRAM 30-m telescope at 1.3 mm wavelen gth (230 GHz) of the quasi-point-like source Mars and the extended sou rce Saturn, that it is possible to eliminate (to a large extent) this wavefront deformation when using a near-focus corrector, on the 30-m t elescope conveniently located on the co-rotating Nasmyth mirror.