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Laser Guide Star System on ESO's VLT Starts Regular Science Operations (Forwarded)



 
 
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Old June 24th 07, 10:55 PM posted to sci.space.news
Andrew Yee[_1_]
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Default Laser Guide Star System on ESO's VLT Starts Regular Science Operations (Forwarded)

ESO Education and Public Relations Dept.

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Text with all links and the photos are available on the ESO Website at URL:
http://www.eso.org/public/outreach/p.../pr-27-07.html
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Contacts:

Markus Kasper, Stefan Stroebele
ESO, Garching, Germany
Phone: +49 89 3200 6359, +49 89 3200 6323

Richard Davies
Max Planck Institute for Extraterrestrial Physics,
Garching, Germany
Phone: +49 89 30000 3298

Domenico Bonaccini Calia
ESO, Garching, Germany
Email: Domenico.Bonaccini (at) eso.org

For Immediate Release: 13 June 2007

ESO Instrument Release 27/07

Free from the Atmosphere

Laser Guide Star System on ESO's VLT Starts Regular Science Operations

An artificial, laser-fed star now shines regularly over the sky of Paranal,
home of ESO's Very Large Telescope, one of the world's most advanced large
ground-based telescopes. This system provides assistance for the adaptive
optics instruments on the VLT and so allows astronomers to obtain images
free from the blurring effect of the atmosphere, regardless of the
brightness and the location on the sky of the observed target. Now that it
is routinely offered by the observatory, the skies seem much sharper to
astronomers.

In order to counteract the blurring effect of Earth's atmosphere,
astronomers use the adaptive optics technique. This requires, however, a
nearby reference star that has to be relatively bright, thereby limiting the
area of the sky that can be surveyed. To surmount this limitation,
astronomers now use at Paranal a powerful laser that creates an artificial
star, where and when they need it.

Two of the Adaptive Optics (AO) science instruments at the Paranal
observatory, NACO and SINFONI, have been upgraded to work with the recently
installed Laser Guide Star (LGS; see ESO 07/06) and have delivered their
first scientific results. This achievement opens astronomers' access to a
wealth of new targets to be studied under the sharp eyes of AO.

"These unique results underline the advantage of using a Laser Guide Star
with Adaptive Optics instruments, since they could not be obtained with
Natural Guide Stars," says Norbert Hubin, head of the Adaptive Optics group
at ESO. "This is also a crucial milestone towards the multi-laser systems
ESO is designing for the VLT and the future E-ELT" (see e.g. ESO 19/07).

The Laser Guide Star System installed at Paranal uses the PARSEC dye laser
developed by MPE-Garching and MPIA-Heidelberg, while the launch telescope
and the laser laboratory was developed by ESO.

"It is great to see the whole system working so well together," emphasises
Richard Davies, project manager of the PARSEC laser.

"To test the laser guide star adaptive optics system to its limits, and even
beyond, we observed a number of galaxies, ranging from a close neighbour to
one that is seen when the universe was very young," explains Markus Kasper,
the NACO Instrument Scientist at ESO.

The first objects that were observed are interacting galaxies. The images
obtained reveal exquisite details, and have a resolution comparable to that
of the Hubble Space Telescope. In one case, it was possible to derive for
the first time the motion of the stars in two merging galaxies, showing that
there are two counter-rotating discs of stars.

"The enhanced resolution that laser guide star adaptive optics provides is
certain to bring important new discoveries in this exciting area," says
Davies.

The astronomers then turned the laser to a galaxy called K20-ID5 which is at
a redshift of 2.2 -- we are seeing this galaxy when the universe was less
than 1/3 of its current age. The image obtained with NACO shows that the
stars are concentrated in a much more compact region than the gas.

"These observations are both remarkable and exciting," declares Kasper.
"They are the first time that it has been possible to trace in such detail
the distributions of both the stars and the gas at an epoch where we are
witnessing the formation of galaxies similar to our own Milky Way."

At the opposite extreme, much nearer to home, LGS-AO observations were made
of the active galaxy NGC 4945. The new LGS observations with NACO resolved
the central parts into a multitude of individual stars.

"It is in galaxies such as these where we can really quantify the star
formation history in the vicinity of the nucleus, that we can start to piece
together the puzzle of how gas is accreted onto the supermassive black hole,
and understand how and when these black holes light up so brightly," says
Davies.

Still closer to home, the LGS system can also be applied to solar system
objects, such as asteroids or satellites, but also to the study of
particular regions of spatially extended bodies like the polar regions of
giant planets, where aurora activity is concentrated. During their science
verification, the scientists turned the SINFONI instrument with the LGS to a
Trans-Neptunian Object, 2003 EL 61. The high image contrast and sensitivity
obtained with the use of the LGS mode permit the detection of the two faint
satellites known to orbit the TNO.

"From such observations one can study the chemical composition of the
surface material of the TNO and its satellites (mainly crystalline water
ice), estimate their surface properties and constrain their internal
structure," explains Christophe Dumas, from ESO.

The VLT Laser Guide System is the result of a collaborative work by a team
of scientists and engineers from ESO and the Max Planck Institutes for
Extraterrestrial Physics in Garching and for Astronomy in Heidelberg,
Germany. NACO was built by a Consortium of French and German institutes and
ESO. SINFONI was built by a Consortium of German and Dutch Institutes and
ESO.

More Information

Normally, the achievable image sharpness of a ground-based telescope is
limited by the effect of atmospheric turbulence. This drawback can be
surmounted with adaptive optics, allowing the telescope to produce images
that are as sharp as if taken from space. This means that finer details in
astronomical objects can be studied, and also that fainter objects can be
observed. In order to work, adaptive optics needs a nearby reference star
that has to be relatively bright, thereby limiting the area of the sky that
can be surveyed to a few percent only. To overcome this limitation,
astronomers use a powerful laser that creates an artificial star, where and
when they need it.

The laser beam takes advantage of the layer of sodium atoms that is present
in Earth's atmosphere at an altitude of 90 kilometres. Shining at a
well-defined wavelength the laser makes it glow. The laser is launched from
Yepun, the fourth 8.2-m Unit Telescope of the Very Large Telescope,
producing an artificial star. Despite this star being about 20 times fainter
than the faintest star that can be seen with the unaided eye, it is bright
enough for the adaptive optics to measure and correct the atmosphere's
blurring effect.

Compared to a normal star, this artificial star has some differing
properties that the associated Laser Guide Star (LGS) Adaptive Optics (AO)
system has to be able to cope with.

A press release, in English and German, is also available from the
Max-Planck Institute.

National contacts for the media:

Belgium: Dr. Rodrigo Alvarez, +32-2-474 70 50
Czech Republic: Pavel Suchan, +420 267 103 040
Finland: Ms. Tiina Raivo, +358 9 7748 8369
Denmark: Dr. Michael Linden-Vnle, +45-33-18 19 97
France: Dr. Daniel Kunth, +33-1-44 32 80 85
Germany: Dr. Jakob Staude, +49-6221-528229
Italy: Dr. Leopoldo Benacchio, +39-347-230 26 51
The Netherlands: Ms. Marieke Baan, +31-20-525 74 80
Portugal: Prof. Teresa Lago, +351-22-089 833
Spain: Dr. Miguel Mas-Hesse, +34918131196
Sweden: Dr. Jesper Sollerman, +46-8-55 37 85 54
Switzerland: Dr. Martin Steinacher, +41-31-324 23 82
United Kingdom: Mr. Peter Barratt, +44-1793-44 20 25

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