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ALMA Telescope Upgrade to Power New Science

5. června 2012

Before its construction is even completed, the new telescope ALMA — the Atacama Large Millimeter/submillimeter Array — is embarking on an upgrade that will help astronomers investigate the earliest galaxies and search for water in other planetary systems. The oversight board for ALMA has authorised the design and building of an additional set of receivers with state-of-the-art performance, which will enable the telescope to access a part of the spectrum of light that it cannot currently study.

ALMA is the world’s largest astronomy project, and this powerful new facility on the Chajnantor plateau in Chile is giving astronomers insight into both how the Universe and its galaxies have evolved since the Big Bang, and how stars and planetary systems formed in our own galaxy. Although only half of its final total of 66 antennas are currently in place at the high-altitude site in northern Chile (see ann12035), ALMA is already operating and making scientific observations with a partial array (see for example eso1137 and eso1216).

ALMA observes the Universe in radio waves: light which is invisible to our eyes. Extremely weak signals from space are collected by the ALMA antennas and focussed onto the receivers, which transform the faint radiation into an electrical signal. The new “Band 5” receivers will be able to detect electromagnetic radiation with wavelengths between about 1.4 and 1.8 millimetres (211 and 163 gigahertz), one of the ranges of the spectrum to which Earth's atmosphere is partially transparent, which allows the light to reach the ALMA antennas.

The new receivers were originally designed, developed, and prototyped by Onsala Space Observatory’s Advanced Receiver Development group, based at Chalmers University of Technology in Gothenburg, Sweden, in collaboration with the Rutherford Appleton Laboratory, UK, and ESO, under the European Commission (EC) supported Framework Programme FP6 (ALMA Enhancement) starting in 2006. Six of these receivers have been built under the FP6 contract and supplied to ALMA (see ann1098).

Over the next five years, all 66 of ALMA’s antennas will be equipped with these new receivers. To do this, including spares, another 67 units need to be built. These will be provided by Europe with contributions from the United States. The European Southern Observatory (ESO) will place the European contract for the cryogenically cooled receivers, and oversee their development. The consortium leader will be NOVA, the research school for astronomy in the Netherlands. The receivers will be fabricated by NOVA in partnership with Onsala Space Observatory’s Advanced Receiver Development group. In North America, the National Radio Astronomy Observatory (NRAO) will build the high-precision oscillators that will tune the receivers, so that the output from all antennas can be precisely combined to make high-resolution images.

The receivers will be used to study some of the earliest galaxies in the Universe and will help us to understand when some of the first stars formed. They will also enhance astronomers' abilities to measure the presence of water — a molecule essential to life — in the dusty disks where planets are believed to form, and in the atmospheres of planets and comets in our own Solar System. Water in space can be tricky to measure accurately, because of the confusing effects of observing through the water vapour in Earth's atmosphere. The way in which ALMA's Band 5 receivers will measure water reduces some of these difficulties.

The decision to fund this enhancement of ALMA, even before the telescope is completed, was made by the ALMA Board in April 2012. On 9 May 2012, the decision was approved by ESO's Finance Committee. The upgrade is expected to be completed in 2016.

ALMA, an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.