A quintuplet of ALMA antennas — and then there were five

On the Chajnantor plateau, the Atacama Large Millimeter/submillimeter Array (ALMA) is growing. On 31 May 2010, the number of ALMA’s state-of-the-art antennas on the 5000-metre-altitude plateau in the Chilean Andes increased to five. This photograph shows the five 12-metre diameter antennas at the Array Operations Site, clustered on the closely spaced foundation pads of what will be ALMA’s “Atacama Compact Array”.

When complete, ALMA will have fifty-four 12-metre and twelve 7-metre diameter antennas, operating together as an interferometer: the signals from the individual antennas are combined in a specialised supercomputer — the ALMA correlator — so that the array of antennas acts as a single, giant telescope. The team of astronomers and engineers have now achieved a successful test linking all of these first five antennas together as an interferometer.

This result follows the successful first measurements with a pair of antennas in October 2009 (see ESO Announcement) and the linkup of three antennas in November (see ESO Press Release eso1001). These milestones have already demonstrated the excellent performance of the instruments, but the addition of yet more antennas represents a further step in ALMA’s growth, and has allowed the team to make some further tests of the correlator that were not possible with fewer antennas.

ALMA will probe the sky in millimetre and submillimetre wavelengths of light. This light comes from vast cold clouds in interstellar space, at temperatures only a few tens of degrees above absolute zero, and from some of the earliest and most distant galaxies in the Universe.

The team are now carrying out additional tests on the antennas, and over the course of the coming months more antennas will arrive on the high site. ALMA will start early scientific observations using a partial array of antennas around 2011, with construction to be completed around 2012.

ALMA, the largest astronomical project in existence, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ESO is the European partner in ALMA.

More info: ESO ALMA web pages