Antenna Teamwork at the ALMA Observatory

Milestone on the way to the observation of the cool regions of the universe succeeded

The three interconnected ALMA antennas © ALMA (ESO / NAOJ / NRAO)
Read out

Milestone for the revolutionary new ALMA observatory: For the first time, astronomers and engineers have succeeded in interconnecting three of the ALMA antennas at their observation site in northern Chile. Thus, extremely detailed observations of the cool regions of the universe, as they should enable ALMA, move one step closer.

On 20 November 2009, the third antenna of the ALMA composite telescope, which was under construction, was installed at the observation site on the Chajnantor Plateau in the Chilean Andes - 5, 000 meters above sea level. Only a short time later, the scientists were able to connect the three 12-meter antennas and use them to observe a celestial object.

More than just babbling a baby

"What we picked up on signals in October, when we could only pair two ALMA antennas together, is like babbling a baby, " said Leonardo Testi, the European ALMA project scientist at ESO. "Our observations with three antennas correspond to the moment when the baby says his first meaningful word - not yet a complete sentence, but very exciting! Interconnecting three antennas is an important step toward our goal of taking unmatched detail-accurate images in the submillimetre wavelength range with ALMA. "

By successfully connecting the three antennas, the electronic systems and software currently installed at ALMA have passed a critical test. Now, the ALMA team is working on a much larger scale network: the final ALMA will be an interferometer made up of at least 66 high-tech antennas, interconnected to work like a single giant telescope. This is to explore the sky at millimeter and submillimeter wavelengths. Only through the merger on a large scale can ALMA achieve the necessary performance.

Get a grip on disruptions

"Interconnecting three (or more) antennas into an interferometer means a huge increase in performance over dual-antenna operation, " explains Wolfgang Wild, the European project manager at ALMA. "Astronomers can thus get a grip on disturbances such as those caused by instrumental noise or atmospheric turbulence. The comparison of the signals received simultaneously with three antennas makes it possible to compensate for such unwanted side effects - something that is impossible in two-antenna operation. "Display

In order to reach this milestone, astronomers set their antennas on a distant extragalactic celestial object: the Quasar B1921-293, which is used at long wavelengths - including the millimeter and submillimeter range of ALMA observations - very bright lights. The result of the combined signal of the three antennas showed that the arrangement works excellently.

First scientific observations from 2011

Over the next few years, ALMA will be extended by several more antennas. From 2011, astronomers will then be able to make initial scientific observations. In the following period, the addition of additional antennas will make the interferometer more and more powerful until the setpoint of at least 66 antennas has been reached.

(idw - Max Planck Institute for Astronomy, 05.01.2010 - DLO)