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ESO press release: Adding New Colours to Interferometry
ESO Press Release 07/04
5 April 2004
For immediate release
Adding New Colours to Interferometry
AMBER joins the VLT Interferometer 
Another vital step has been accomplished as planned towards full operation of the ESO Very Large Telescope Interferometer (VLTI) at the Paranal Observatory in Chile, one of the world’s foremost astronomical facilities.
In the night of March 20-21, 2004, a team of astronomers and engineers from France, Italy, Germany and ESO celebrated the successful assembly and completion of the first on-line tests of the latest of the first-generation VLTI instruments, the Astronomical Multiple BEam Recombiner (AMBER). They combined the two beams of light from the southern star Theta Centauri from two test telescopes ("siderostats" with 40-cm aperture, cf. ESO PR 06/01) to produce strong and clear interferometric fringes. Equally successful observations were then obtained on the bright star Sirius, and consistently repeated during the following nights.
A joint project
This is the most promising result of about 7 years of dedicated work by a team of over 40 astronomers and engineers. The AMBER instrument has been developed by a European consortium of seven research institutes in three ESO member countries, the main partners being: Laboratoire d’Astrophysique de Grenoble (LAOG), Laboratoire Universitaire d’Astrophysique de Nice (LUAN) and Observatoire de la Côte d’Azur in France, Max-Planck-Institut für Radioastronomie (MPIfR) in Bonn, Germany, and Osservatorio Astrofisico di Arcetri (OAA; part of INAF, the Italian National Institute for Astrophysics) in Florence, Italy.
The total cost of AMBER is of the order of 5.9 million Euros, mostly contributed by the members of the consortium. It was built through an agreement with ESO, which rewards the consortium solely with guaranteed observing time. According to the contract, the consortium will receive 60 observing nights to be spread among two or three of the four 8.2-m VLT Unit Telescopes and 130 nights with the four Auxiliary Telescopes over a period of eight years.
AMBER: soon to join three light beams at once
The AMBER instrument is mounted on a 4.2 x 1.5 m precision optical table, placed in the VLT Interferometric Laboratory at the top of the Paranal mountain, cf. PR Photo 09/04. The total shipping weight of the instrument and its extensive associated electronics was almost 4 tons.
AMBER is the latest addition to the VLTI and completes the planned set of first-generation instruments for this facility. It continues the success story of the interferometric mode of the VLT, following the unique initial scientific results obtained by the VINCI and MIDI instruments, the installation of the first MACAO adaptive optics systems and the recent arrival of the first 1.8-m Auxiliary Telescope at Paranal (ESO PR 01/04).
The interferometric technique can achieve images, as sharp as those of a telescope with a diameter equivalent to the distance between the telescopes in the interferometer. For the VLTI, this distance can be as large as 205 meters, resulting in a resolution of 0.001 arcsec in the near-infrared spectral region (at 1 μm wavelength). The latter measure corresponds to about 2 metres on the surface of the Moon.
AMBER is a very powerful complement to the other instruments already installed at the VLTI and offered to the astronomical community. AMBER is indeed sensitive in the near-infrared wavelength region of 1 to 2.5 microns while the present instrument, MIDI, covers the 8 to 13 microns range. Moreover, AMBER will be able to perform spectroscopic measurements with a spectral resolution up to 10,000.
AMBER will also combine three light beams from as many telescopes - this is a world premiere for large telescopes such as the VLT. The ability to combine three beams, rather than just two as in a conventional interferometer, provides a substantial increase in the efficiency of observations, permitting astronomers to obtain simultaneously three baselines instead of one. The combination of these three baselines also permits the computation of the so-called closure phase, an important mathematical quantity that can be used in imaging applications.
Exciting scientific opportunites
These observational capabilities, characterized by the highest possible image sharpness and enormous sensitivity, make AMBER a unique instrument for addressing a large number of frontline astronomical topics. In particular, it is expected that AMBER will greatly contribute by:
After the first very successful tests, AMBER is now entering a long phase of observational tests that will serve to adjust its many parts and to optimize its performance. They include tests at the end of May to be made by combining the light beams from two, then three of the 8.2-m VLT Unit Telescopes. In 2005, the instrument will be offered to the astronomical community who will then be able to use it, either with the Unit Telescopes or with their little brothers, the 1.8-m moveable Auxiliary Telescopes.
 This ESO press release is coordinated and issued simultaneously with releases in the respective languages by the Centre National de la Recherche Scientifique in France (CNRS Press Release), the Max-Planck Institut für Radioastronomie in Germany (MPI Press Release) and Osservatorio Astrofisico di Arcetri in Italy (INAF Press Release).
 The institutes taking part in the AMBER consortium are :
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