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Halfway There: 33 ALMA Antennas on Chajnantor

15 Maggio 2012

On the Chajnantor plateau in northern Chile, construction of the Atacama Large Millimeter/submillimeter Array (ALMA), the most complex ground-based astronomy observatory in the world, continues apace. On 12 May 2012, another ALMA antenna was carried up to Chajnantor, bringing the total on the plateau to 33. This marks a half-way point for ALMA, as the telescope will have a total of 66 antennas when completed in 2013. The giant antennas, fifty-four of them with 12-metre-diameter dishes, and twelve with 7-metre-diameter dishes, use sensitive receivers to detect millimetre- and submillimetre-wavelength light from the cosmos.

The first of the antennas made the trip up to the 5000-metre-altitude Array Operations Site in September 2009 (see eso0935). Now, as ALMA approaches completion, antennas are arriving at an increasing rate.

The state-of-the-art ALMA antennas, which weigh about 100 tonnes each, need a custom-constructed transporter vehicle to move them between the Operations Support Facility and the higher Array Operations Site. These twin transporters, as well as 25 antennas out of the final total of 66, are among ESO’s many contributions to the project [1]. The transporters — massive machines named Otto and Lore — are 20 metres long, 10 metres wide and 6 metres high, and each has 28 tyres. They are also used to move the antennas between positions on the plateau. The minimum distance between antennas is 15 metres and they can be all positioned within a radius of 150 metres, or spaced up to 16 kilometres apart. This gives ALMA a powerful variable “zoom”.

Although not all the antennas have arrived at Chajnantor, ALMA is already operating and making Early Science observations with a partial array (see eso1137). ALMA is the most powerful telescope for observing the cool Universe — molecular gas and dust as well as the relic radiation of the Big Bang. With ALMA, astronomers are studying the building blocks of stars, planetary systems, galaxies, and life itself.

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.

Notes

[1] Twenty-five European ALMA antennas are being provided by ESO through a contract with the European AEM Consortium. ALMA will also have 25 antennas provided by North America, and 16 by East Asia.