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ESO press release: Adding New Colours to Interferometry
Monday 5 April 2004

ESO Press Release 07/04

5 April 2004

For immediate release

Adding New Colours to Interferometry

AMBER joins the VLT Interferometer [1]

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

ESO PR Photo 09a/04

ESO PR Photo 09a/04

AMBER at the VLT Interferometric Laboratory

[Preview - JPEG: 534 x 400 pix - 68k]
[Normal - JPEG: 1067 x 800 pix - 665k]

Caption: ESO PR Photo 09a/04 shows the AMBER instrument in the VLT Interferometric Laboratory at Paranal.

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.

ESO PR Photo 09b/04

ESO PR Photo 09b/04

The AMBER instrument (detail)

[Preview - JPEG: 435 x 400 pix - 74k]
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Caption: ESO PR Photo 09b/04 shows in the foreground some of the mirrors and optical fibers (yellow cables), as well as the dichroic mirrors by means of which the light beams from the three telescopes are split into separate wavebands.

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:

  • Obtaining very detailed images of dusty discs around young stars for studies of the formation of stars and of planets in other solar systems. With its exceedingly sharp view, AMBER will be able to observe structures of the size of Mercury’s orbit in stars located in the major nearby star-forming regions.
  • Providing new images and spectra that will improve our understanding of the physics of black holes believed to be present in the central parts of all galaxies. AMBER will make it possible to look at the innermost parts of other galaxies, thereby providing information on their central engines.
  • Detecting for the first time the light of "hot Jupiters", that is planets orbiting very close to their parent stars. It will be possible to determine the mass of these planets and to study their atmosphere directly by means of spectral observations. This is equivalent to detecting - and analysing - the light of a dragonfly in the vicinity of a lighthouse.

Next Steps

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.


[1] 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).

[2] The institutes taking part in the AMBER consortium are :

  • LAOG - Laboratoire d’Astrophysique de Grenoble, France
  • LUAN - Laboratoire d’Astrophysique Universitaire de Nice, France
  • MPIfR - Max-Planck Institut für Radioastronomie, Bonn, Germany
  • OAA - Osservatorio Astrofisico di Arcetri (part of INAF, the Italian National Institute for Astrophysics), Florence, Italy
  • OCA - Observatoire de la Côte d’Azur, France


Andrea Richichi
European Southern Observatory
Garching, Germany
Phone : +49 89 3200 6803
Email :

Romain Petrov
Universite de Nice
Sophia Antipolis, France
Phone : +33 (0) 492076347
Email :

Fabien Malbet
Observatoire des sciences de l’univers
Grenoble, France
Phone : +33 (0) 476635833
Email :

Franco Lisi
Osservatorio Astrofisico di Arcetri (OAA - INAF)
Florence, Italy
Phone : +39 055 2752289
Email :

Gerd Weigelt
Max-Planck-Institut für Radioastronomie
Bonn, Germany
Phone: +49 228 525 243
Email :

Pierre Antonelli
Observatoire de la Côte d’Azur
Nice, France
Phone : +33 (0) 492003064
Email :

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