Press Release

MONA, LISA and VINCI Soon Ready to Travel to Paranal

First Instruments for the VLT Interferometer

13 November 2000

A few months from now, light from celestial objects will be directed for the first time towards ESO's Very Large Telescope Interferometer (VLTI) at the Paranal Observatory (Chile). During this "First Light" event and the subsequent test phase, the light will be recorded with a special test instrument, VINCI (VLT INterferometer Commissioning Instrument). The main components of this high-tech instrument are aptly named MONA (a system that combines the light beams from several telescopes by means of optical fibers) and LISA (the infrared camera). VINCI was designed and constructed within a fruitful collaboration between ESO and several research institutes and industrial companies in France and Germany. It is now being assembled at the ESO Headquarters in Garching (Germany) and will soon be ready for installation at the telescope on Paranal. With the VLTI and VINCI, Europe's astronomers are now entering the first, crucial phase of an exciting scientific and technology venture that will ultimately put the world's most powerful optical/IR interferometric facility in their hands.

The VLT Interferometer (VLTI)

VINCI (VLT INterferometer Commissioning Instrument) is the "First Light" instrument for the Very Large Telescope Interferometer (VLTI) at the Paranal Observatory (Chile). Early in 2001, it will be used for the first tests of this very complex system. Subsequently, it will serve to tune this key research facility to the highest possible performance.

The VLTI is based on the combination of light (beams) from the telescopes at Paranal. Of these, the four 8.2-m Unit Telescopes are already in operation - they will soon be joined by three 1.8-m telescopes that can be relocated on rails, c.f. ESO Press Photo eso9951b.

By means of a system of mirrors, the light from two or more of these telescopes will be guided to the central Interferometric Laboratory, at the center of the observing platform on Paranal. Information about the heart of this complex system, the Delay Lines that are located in the underground Interferometric Tunnel, is available with the recent ESO Press Photos eso0032.

The VLTI will later receive other front-line instruments, e.g. AMBER, MIDI and PRIMA. When fully ready some years from now, the VLTI will produce extremely sharp images. This will have a major impact on different types of exciting astronomical observations, e.g.:

• the direct discovery and imaging of extra-solar planets comparable to Jupiter,
• the discovery and imaging of low-mass stars such as brown dwarfs,
• observations of star-forming regions and to better understand the physical processes that give birth to stars,
• spectral analysis of the atmospheres of nearby stars, and
• imaging the objects of the very core of our Galaxy and the detection of black holes in active nuclei of galaxies.

The VINCI test instrument

The new instrument, VINCI, will soon be delivered to Paranal by the Département de Recherche Spatiale (Department for Space Research), a joint unit of the Centre Nationale de la Recherche Scientifique (French National Centre for Scientific Research) and the Paris Observatory.

VINCI is a functional copy of the FLUOR instrument - now at the IOTA (Infrared Optical Telescope Array) interferometer - that has been upgraded and adapted to the needs of the VLTI.

FLUOR was developed by the Département de Recherche Spatiale (DESPA) of the Paris Observatory. It was used in 1991 at the Kitt Peak National Observatory (Arizona, USA), for the first (coherent) combination of the light beams from two independent telescopes by means of optical fibers of fluoride glass. It has since been in operation for five years as a focal instrument at the IOTA Interferometer (Mount Hopkins, Arizona, USA) within a collaboration with the Harvard Smithsonian Center for Astrophysics), producing a rich harvest of scientific data.

The VINCI partners

The VINCI instrument is constructed in a collaboration between ESO (that also finances it) and the following laboratories and institutes:

• DESPA (Paris Observatory) provides the expertise, the general concept, the development and integration of the optomechanics (with the exception of the camera) and the electronics,
• Observatoire Midi-Pyrénées that produces the control software
• The LISA infrared camera is developed by the Max-Planck-Institut für Extraterrestrische Physik (Garching, Germany), and
• ESO provides the IR camera electronics and the overall observational software and is also responsible for the final integration.

DESPA delivered VINCI to ESO in Garching on September 27, 2000, and is now assembling the instrument in the ESO optical workshop. It will stay here during three months, until it has been fully integrated and thoroughly tested. It will then be shipped to Paranal at the beginning of next year. After set-up and further tests, the first observations on the sky are expected in late March 2001.

Fluoride fibers guide the light

The heart of VINCI - named MONA - is a fiber optics beam combine unit. It is the outcome of a fertile, 10-year research partnership between Science (DESPA) and Industry ("Le Verre Fluoré" [2]).

Optical fibers will be used to combine the light from two telescopes inside VINCI. Since the instrument will be working in the near-infrared region of the spectrum (wavelength 2-2.5 µm), it is necessary to use optical fibers made of a special type of glass that is transparent at these wavelengths. By far the best best material for this is fluoride glass. It was invented by one of the co-founders of the company "Le Verre Fluoré", the only manufacturer of this kind of highly specialized material in the world.

Optical fibers of fluoride glass from this company are therefore used in VINCI. They are of a special type ("monomode") with a very narrow core measuring only 6.5 µm (0.065 mm) across.

Light that is collected by one of the telescopes in the VLTI array (e.g., by the 50 m 2 mirror of a VLT Unit Telescope) is guided through the VLTI system of optics and finally enters this core.

The fibers guide the light and at the same time "clean" the light beam by eliminating the errors introduced by the atmospheric turbulence, hereby improving the accuracy of the measurements by a factor of 10.

DESPA has shown that this is indeed possible by means of real astronomical observations with the FLUOR experiment. Following this positive demonstration, it has been decided to equip the instrumentation of all interferometers currently under construction with fibers or equivalent systems.

Notes

[1] This ESO Press Release is issued in conjunction with communications from the Centre Nationale de la Recherche Scientifique (French National Centre for Scientific Research) and the Paris Observatory.

[2] The manufacturer "Le Verre Fluoré" is the only one in the world that produces "monomode" fiber optics couplers made of fluoride glass. The development of these high-tech systems was initiated in 1988 by a grant from the French Ministry for Research and Technology. Its use by DESPA in the FLUOR instrument, which served as a testing bench, has allowed to further improve this technology.

Contacts

Andreas Glindemann
ESO
Garching, Germany
Tel: +49-89-32006590
Email: aglindem@eso.org

Pierre Kervella
ESO
Garching, Germany
Tel: +49-89-32006472
Email: pkervell@eso.org

Vincent Coudé Du Foresto
Observatoire de Paris
Paris, France
Tel: +33-1-45077961
Email: Vincent.Foresto@obspm.fr

Gwenaël Mazé
Le Verre Fluoré
Tel: +33-2-99053130
Email: gwenael.maze@wanadoo.fr

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