17 December 2010
Media Contact:
Alexia Sagot
+33 (0) 1 40 51 23 97
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Gerard Rousset
+33 (0) 1 45 07 75 49; cell: +33 (0) 6 26 52 37 98
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Eric Gendron
+33 (0) 1 45 07 79 18
eric.gendron@obspm.fr
Text (in French) and images:
http://www.grandpublic.obspm.fr/Une-super-technique-d-optique
A POWERFUL INNOVATIVE ADAPTIVE-OPTICS
TECHNOLOGY TO SURVEY THE EARLY UNIVERSE
Adaptive optics allows one to observe the sky without suffering
perturbations from atmospheric turbulence. Now, a French-British team
has demonstrated a major improvement of this technology, opening the
study of very faint sources in a very large field of view. It was done
with the CANARY demonstrator installed at the William Herschel 4.2m
telescope on La Palma, Canary Islands, Spain. The analysis of the
first results obtained in September 2010 shows that the system
performs very well. This test validates the feasibility of the EAGLE
instrument, dedicated to the characterization of 20 galaxies of the
early universe at a time, distributed within a 5 arcminute diameter
field of view (1/6 the apparent width of the full Moon), on the future
42 meter European Extremely Large Telescope of the European Southern
Observatory (ESO) to be installed in the Atacama desert, Chile.
The question of how the universe evolved from the Big Bang into its
highly structured state of stars, galaxies, and clusters of galaxies
is a key question for modern cosmology. If we could look back to the
early epoch when the first stars started to emit light, we could
observe the formation of the very first galaxies.
In order to make such observations, one of the key tools will be an
optical telescope of unprecedented size. The largest telescope planned
is the European Extremely Large Telescope, 42 meters in diameter. Such
a telescope must be ground-based, and its imaging qualities should
approach those of a space telescope. This means overcoming the effects
of looking through the inevitable atmospheric turbulence above the
telescope. The technology to do this has been under development for
the last 20 years or so and is called adaptive optics. It uses special
deformable mirrors that can adapt themselves to cancel the changing
atmospheric distortions of the light waves many hundreds of times per
second.
Hitherto, adaptive optics has only operated over fairly limited fields
of view. To survey the early universe efficiently, however, larger
areas of sky must be corrected all at once. This is the role of the
EAGLE instrument, designed in France and the United Kingdom. It will
be able to look in detail at 20 target galaxies at a time, each one of
which will be separately corrected for atmospheric distortion.
However, the first galaxies are too faint to allow us to measure the
atmospheric distortions using their own light as a reference. It is
therefore required to find a number of guide stars bright enough for
this purpose in the field of view. It is also envisioned to generate
artificial laser guide stars. Moreover, using only one deformable
mirror for compensating for the whole field of view, as is done in
conventional adaptive optics, is not feasible. Because of the very
small size of the first galaxies, it is instead only required to
compensate for turbulence in a few small image zones distributed
throughout the whole field of view. The new technology, called
Multi-Object Adaptive Optics (MOAO), implements one deformable mirror
per target in a dedicated optical train. All deformable mirrors are
being controlled, from all the measurements performed on all the guide
stars, through a global tomography approach to measuring the
atmosphere. This new technique was demonstrated on-sky for the first
time in September 2010 by the EAGLE team at the William Herschel 4.2m
telescope on La Palma in the Canary Islands, Spain.
The William Herschel Telescope is exactly 1/10 the diameter of the
future European Extremely Large Telescope. The first observations made
with CANARY were a spectacular success. The new technology operated at
the hoped-for performance level the first time it was used.
Photo 1 shows the image of a test star with the correction system
switched off and then with it on. The achieved performance is very
similar to that obtained by conventional adaptive optics under the
same conditions. Corrections were applied 150 times every second using
information gathered from three other off-axis stars. This information
was used to infer the corrections required to sharpen the view in the
direction of the test star. This crucial tomography of the atmosphere
above the telescope and the deformable mirror control are the novel
achievements of CANARY.
The next step will be to repeat this experiment but using artificial
guide stars generated in the atmosphere using powerful lasers. This
technique has been used elsewhere, but never to perform the
tomographic measurements required by CANARY. The use of laser stars is
essential for EAGLE today and for the E-ELT in the future.
Images & Captions
Photo 1:
http://www.grandpublic.obspm.fr/IMG/jpg/003-9.jpg
Images recorded in the near infrared (1.65 microns) by CANARY. Right,
without any correction. Left, with correction recovering the
telescope’s diffraction limit.
Photo 2:
http://www.grandpublic.obspm.fr/IMG/jpg/003-8.jpg
The 4.2-meter William Herschel Telescope at Roque de Los Muchachos, La
Palma, Canary Islands, Spain, with its laser shooting to create an
artificial guide star in the upper atmosphere. Courtesy Tibor Agocs,
Isaac Newton Group.
# # #
The institutions involved in the development and the first
demonstration of CANARY:
* Laboratoire d’Etudes Spatiales et d’Instrumentations en
Astrophysique LESIA (Observatoire de Paris, CNRS, Universite Paris
Diderot, Universite Pierre et Marie Curie), France
* Laboratoire d’Etudes des Galaxies, Etoiles, Physique et
Instrumentation GEPI (Observatoire de Paris, CNRS, et Universite Paris
Diderot), France
* Durham University and Astronomy Technology Centre, United Kingdom
Professor Gerard Rousset of LESIA and Dr. Richard Myers of Durham
University are co-leaders of the CANARY Project. The team also
acknowledges contributions from Engineering and Project Solutions Ltd.
and the staff of the Isaac Newton Group of telescopes, who operates
the William Herschel Telescope.
Institutions involved in EAGLE:
* Laboratoire d’Astrophysique de Marseille LAM (CNRS, Universite de
Provence), LESIA, GEPI, France
* Office National d’Etudes et de Recherches Aeropsatiales (ONERA), France
* UKATC, Durham University; EAGLE is led by Dr. Jean-Gabriel Cuby of
LAM and Professor Simon Morris of Durham University.
Financial support:
* Agence Nationale de la Recherche, CNRS, Observatoire de Paris,
Universite Paris Diderot
* Science and Technology Facilities Council, Durham University
* European Commission