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Atacama Large Millimeter Array
The Atacama Large Millimeter/submillimeter Array (ALMA) is an international astronomy project that consists of an astronomical interferometer formed from an array of radio telescopes, located at Llano de Chajnantor Observatory in the Atacama desert in northern Chile. The telescope is expected to revolutionise modern astronomy by providing an insight on star formation in the early universe and imaging local star and planet formation in great detail. With a cost in excess of 1 billion US dollars, it is the most ambitious ground-based telescope currently under construction.
Overview
The telescopes and their receivers are capable of detecting sub-millimeter and millimeter wavelengths. The array will have much higher sensitivity and higher resolution than existing sub-millimeter telescopes such as the single-dish James Clerk Maxwell Telescope or existing interferometer networks such as the Submillimeter Array or the IRAM Plateau de Bure facility. By moving the antennas at regular intervals, the resolution of the array and the size of object that can be imaged will be altered, producing a "zoom-lens" capability, similar to that employed at the Very Large Array. The high sensitivity is mainly achieved through the large numbers of telescopes that will make up the array. Whilst 64 12-m dishes were originally envisaged, it is now possible that there will ultimately only be 50. The American and European partners have each placed orders for 25 antennas, with options for an additional seven. Japan is also contributing antennas in the form of the Atacama Compact Array (ACA) which will also be located at the ALMA site. By using smaller antennas than ALMA (12 7-m and 4 12-m dishes are planned) larger fields of view can be imaged at a given frequency. The ACA will work together with ALMA in order to enhance the latter's wide-field imaging capability.
Funding
ALMA was initially a 50-50 collaboration between ESO and the North American partners. The array has been extended with the help of the new East Asian, Spanish and Chilean partners. ALMA is the largest and most expensive ground-based astronomical project currently under construction (current cost estimate is 1.5 billion Y2000 US dollars).
European Partners
European Southern Observatory and the European Regional Support Center
Spanish Ministry of Science and Technology
North American Partners
National Science Foundation via the National Radio Astronomy Observatory and the North American ALMA Science Center
National Research Council of Canada
East Asian Partners
National Astronomical Observatory of Japan (NAOJ) under the National Institutes of National Sciencs (NINS)
ALMA-Taiwan at the Academia Sinica Institute of Astronomy & Astrophysics (ASIAA)
Other partners
Republic of Chile
Assembly
The complex will be built primarily by European, US, Japanese and Canadian companies (including General Dynamics) and universities. Three prototype antennas have undergone evaluation at the Very Large Array site in New Mexico since 2002. Alcatel Alenia Space, a consortium of manufacturers from France, Italy, and Germany, has been signed up to provide 25 of the antennas, the largest-ever European industrial contract. The first antenna will be delivered in 2007, and the rest at about one per month, finishing in 2011.
Transporting antennas to the site
Transporting the 115-tonne antennas from the base camp at 2900 m altitude to the site at 5000 m presents enormous problems. The solution chosen is to use two purpose-built 28-wheel self-loading heavy haulers of bold design. The vehicles are made by Scheuerle Fahrzeugfabrik in Germany and each is 10m wide, 20m long and 6 m high, weighing 130 tonnes. They are powered by twin 500 kW diesel engines. The transporters, which feature a driver's seat designed to accommodate an oxygen tank to aid breathing the thin high-altitude air, can pick up the antennas and place them precisely at the site. The first vehicle was completed and tested in July 2007. "Giant truck set for sky-high task." BBC News website, 30 July 2007. Retrieved 31 July 2007.
General information
ALMA construction and operations are led on behalf of North America by the National Radio Astronomy Observatory (NRAO). NRAO is managed by Associated Universities, Inc (AUI). ALMA construction and operations are led on behalf of Europe by ESO and Japan by the National Astronomical Observatory of Japan (NAOJ).
Administration of the ALMA site in Chile is lead by ESO.
Project detail
50 to 64 antennas of 12 meter diameter located at an elevation of 5,000 m at Llano de Chajnantor Observatory, enhanced by a compact array of 4 x 12m and 12 x 7m antennas
Imaging instrument in all atmospheric windows between 10 mm and 350 micrometres
Array configurations from approximately 150 meters to 14 km
Spatial resolution of 10 milliarcseconds, 10 times better than the Very Large Array (VLA) and the Hubble Space Telescope
The ability to image sources arcminutes to degrees across at one arcsecond resolution
Velocity resolution under 50 m/s
Faster and more flexible imaging instrument than the VLA
Largest and most sensitive instrument in the world at millimeter and submillimeter wavelengths
Point source detection sensitivity 20 times better than the VLA
See also
List of observatories
CARMA a sensitive millimeter-wave array operated by a consortium including Caltech, University of California Berkeley, University of Illinois, University of Maryland and University of Chicago.
James Clerk Maxwell Telescope The most sensitive existing sub-millimeter telescope
Plateau de Bure Interferometer, one of the most successful existing millimeter-wave arrays, which is operated by IRAM.
Atacama Submillimeter Telescope Experiment
External links
Webcam showing array construction work at the Operations Support Facility further down the mountain
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Atacama Large Millimeter Array
