Mullard Radio Astronomy Observatory
The Ryle Telescope (RT)
The Ryle Telescope, formerly known as the 5-km Telescope, was originally designed as an 8-element E-W interferometer with the objective of mapping individual radio sources with an angular resolution as good as that of large optical telescopes when it was built in 1971. During its lifetime it has operated at 5,2.7,15 and 31 GHz and, at the higher frequencies, was the first radio interferometer to give subarcsecond images of radio galaxies and quasars. The elements are equatorially mounted 13 m Cassegrain antennas which were originally located on an E-W baseline, four fixed at 1.2 km intervals and four movable on a 1.2 km rail track, giving a range of possible baselines from 18 m to 4.8 km. For high-resolution imaging, the mobile aerials were arranged along the track, to give uniform baseline coverage to 4.8 km; for low-brightness astronomy (e.g. the Sunyaev-Zeldovich effect) the mobile aerials were arranged in a ‘compact array’, with a maximum baseline of about 100 m. All aerial pairs were correlated, so some long baseline data were always available, even in the ‘compact array’ configuration.
Following its initial career making high-resolution maps of radio galaxies and quasars the (then 5-km) Telescope went through a series of upgrades in the late 1980s to improve its sensitivity and was renamed the Ryle Telescope in honour of its original designer. These upgrades were motivated by the growth of interest in the field of Cosmic Microwave Background astronomy and the possibility of observing the ‘shadowing’ of the CMB radiation by foreground clusters of galaxies (the Sunyaev-Zeldovich effect). The enhanced sensitivity of the Ryle to changes in surface-brightness enabled it to map the dip in the CMB radiation for several such clusters. Meanwhile, other telescopes such as the CAT and the VSA which were studying the irregularities in the CMB itself required some means of removing the effects of faint radio sources from their maps. By performing surveys of the same areas of sky with the Ryle Telescope the brightnesses of these sources could be measured and subtracted from the corresponding CAT or VSA maps. Another fruitful observational area for the Ryle unrelated to the CMB was monitoring the flux of galactic variable sources.
The Ryle Telescope has now been reconfigured and incorporated into the Arcminute Microkelvin Imager – AMI.
For information on other MRAO telescopes, follow the links on the left.