Light from Four Telescopes Combined at ESO's Paranal Observatory

4 November 2010

Light coming from the four 1.8-metre Auxiliary Telescopes at the European Southern Observatory’s Very Large Telescope Interferometer (VLTI) based in Paranal, Chile, has been successfully combined for the first time using a new visiting instrument called PIONIER [1]. This is an important step towards unleashing the full potential of the VLTI to use multiple telescopes together to reveal fine detail in distant objects. A joint team from Grenoble LAOG [2] and ESO achieved this very challenging feat of engineering only five days after unpacking the equipment on the mountain.

The VLTI engineers had to control the distance traversed by the light from the widely separated telescopes with an accuracy of about one hundredth of the thickness of a strand of human hair. Once the light reached PIONIER, it was then channelled into the heart of the instrument: a remarkable optical circuit [3], smaller than a credit card, that finally brought the light waves from the different telescopes together in a very precise way so that they could create interference. The resulting resolving power of the telescope array has the sharpness not of the individual 1.8-metre Auxiliary Telescopes, but that of a much bigger “virtual telescope” about 100 metres across, limited only by how far apart the telescopes can be positioned.

PIONIER, developed at LAOG in Grenoble, France, is a visiting instrument at the Paranal Observatory, complementing ESO’s existing AMBER and MIDI instruments [4]. AMBER has previously combined the light from three of the telescopes at the VLTI to study many objects, including the surface of the variable star T Leporis (eso0906). PIONIER, however, will eventually allow the VLTI to go one stage further; with the additional information that a fourth telescope brings to the table, it should be possible to use complex mathematical processing techniques to create more detailed images. The PIONIER team hopes to produce its first images by early 2011.


[1] PIONIER is funded by Université Joseph Fourier, LAOG, INSU-CNRS (ASHRA-PNPS-PNP) ANR 2G-VLTI ANR Exozodi. LAOG is part of the Grenoble Observatory (OSUG).

[2] Laboratoire d’Astrophysique de Grenoble

[3] This integrated optics circuit has been developed at CEA-LETI (Grenoble,France) in collaboration with LAOG.

[4] AMBER and MIDI links


  • More information about PIONIER on the Consortium’s web pages


Jean-Baptiste Le Bouquin
LAOG, France

Gérard Zins
LAOG, France

Jean-Philippe Berger
ESO, Chile
Tel: +54 2 463 3103

Pierre Labeye
Research Engineer, CEA-LETI, France
Tel: +33 4 38 78 59 37

Richard Hook
ESO, La Silla, Paranal, E-ELT and Survey telescopes Public Information Officer
Garching, Germany
Tel: +49 89 3200 6655
Mobile: +49 151 1537 3591

About the Announcement



The PIONIER instrument
The PIONIER instrument