|
The Parkes telescope was designed to be able to observe with high
efficiency at 21cm, the wavelength of the astronomically immportant
neutral hydrogen spectral line. But early experience indicated with
could observe at shorter wavelengths (or higher frequencies). In a
paper in 1965, Broten et al wrote: "Recent research in radio
astronommy has shown the desirability of making observations at
shorter and shorter wavelengths. Although designed originally for
operation at a wavelength of 21cm, the Australian 210-ft telescope has
given satisfactory performances at 11cm, and operation at still
shorter wavelengths appeared possible... A wavelength of 6cm was
therefore chosen for test and measurements were made with a crystal
receiver having an intermediate frequency bandwidth of 10 Mc/s.
... the mean observed beamwidth is 4.1 minutes of arc, in close
agreement with the theoretical value. At long wavelengths the
aperture efficincy, calculated from the angular characteristics of the
feed, mesh leakage and aperture blockage, is 62%. At 6cm and zero
zenith angle, the measured aperture efficiency is 34.5%." Their paper
included the image above of the nearby radio galaxy Pictor A. The isophotes
indicate relative brightness (contour level 1.0 equals 2.6 K antenna
temperature) and the direction of polarisation of the two components
are also indicated. Previous ADAPs have shown more recent, higher
resolution images of Pictor A, based on deep ATCA and X-ray
observations on
28 Jan 2015
and
3 Nov 2015.
(Image credit: Broten et al. 1965 Australian Journal of Physics, 18, 85)
|
