The Very Small Array
The Very Small Array
The Very Small Array (VSA) was a collaboration between Jodrell Bank Observatory, The University of Cambridge (Cambridge Astrophysics) and the Instituto de Astrofisica de Canarias (Tenerife). The project received funding of over 2.5 million pounds (about $4 million US) from the United Kingdom Particle Physics and Astronomy Research Council - PPARC.
The objective of the VSA was to extract the cosmological information encoded in the amplitude of primordial fluctuations on different angular scales (the angular power spectrum) in which there are predicted to be several board peaks. The position and amplitude of these peaks are governed by both the material content and physical processes present in the very early universe. An interferometric array, like the VSA, measures directly the angular spectrum allowing an analysis which by-passes the problems introduced by having to generate a map as an intermediate stage.
As shown in the picture, the VSA consisted of a number of receivers with horn-reflector antennas, forming an aperture synthesis array. This works by taking the radio signals received by each element and combining them in a device known as a 'correlator'. The correlator outputs are the response to the sky brightness distribution filtered by the intereference pattern formed by two antennas and corresponds to a point in the angular power spectrum. Many possible antenna pairs (91 in this case) means many samples over the spectrum. A detailed map can also be formed from the summation of these individual intereference patterns. The most troublesome effects, such as atmospheric contributions and emission from the ground, are strongly suppressed. The VSA was surrounded by a large metal shield to cut down interference from man-made sources of microwaves, and the ground, which looks very hot to a sensitive radio telescope (300 K vs 2.7 K for the CMB!).
After construction and several months of tests, the telescope was shipped and installed at the Teide Observatory, Tenerife, in December 1999 (see pictures). Three months of commissioning were completed when the full complement of 14 antennas and two 3.5 metre parabolic dishes (source substractors) were added.
Observations were carried out from April 2000 to August 2002; in a 'compact' configuration to measure the CMB angular power spectrum over the first few 'Doppler peaks' the results of which are reported here. Then an 'extended' configuration using larger horn-reflectors to cover smaller angular and hence a higher range of the power spectrum.
The Very Small Array: