The Sky Through Three Giant Eyes (Forwarded)

ESO Education and Public Relations Dept.

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Contacts:

Jorge Melnick
ESO
Phone: +49 89 3200 6297

Romain Petrov
LUAN/CNRS/UNSA, Nice, France
Phone: +33 4 92 07 63 47

Fabien Malbet
LAOG/CNRS/UJF, Grenoble, France
Phone: +33 4 76 63 58 33

For Immediate Release: 21 February 2007

ESO Instrument Release 06/07

The Sky Through Three Giant Eyes

AMBER Instrument on VLT Delivers a Wealth of Results

The ESO Very Large Telescope Interferometer, which allows astronomers to
scrutinise objects with a precision equivalent to that of a 130-m
telescope, is proving itself an unequalled success every day. One of the
latest instruments installed, AMBER, has led to a flurry of scientific
results, an anthology of which is being published this week as special
features in the research journal Astronomy & Astrophysics.

"With its unique capabilities, the VLT Interferometer (VLTI) has created
itself a niche in which it provide answers to many astronomical questions,
from the shape of stars, to discs around stars, to the surroundings of the
supermassive black holes in active galaxies," says Jorge Melnick (ESO),
the VLT Project Scientist. The VLTI has led to 55 scientific papers
already and is in fact producing more than half of the interferometric
results worldwide.

"With the capability of AMBER to combine up to three of the 8.2-m VLT Unit
Telescopes, we can really achieve what nobody else can do," added Fabien
Malbet, from the LAOG (France) and the AMBER Project Scientist.

Eleven articles will appear this week in Astronomy & Astrophysics' special
AMBER section. Three of them describe the unique instrument, while the
other eight reveal completely new results about the early and late stages
in the life of stars.

The first results presented in this issue cover various fields of stellar
and circumstellar physics. Two papers deal with very young solar-like
stars, offering new information about the geometry of the surrounding
discs and associated outflowing winds. Other articles are devoted to the
study of hot active stars of particular interest: Alpha Arae, Kappa Canis
Majoris, and CPD:57o2874. They provide new, precise information about
their rotating gas envelopes.

An important new result concerns the enigmatic object Eta Carinae. Using
AMBER with its high spatial and spectral resolution, it was possible to
zoom into the very heart of this very massive star. In this innermost
region, the observations are dominated by the extremely dense stellar wind
that totally obscures the underlying central star. The AMBER observations
show that this dense stellar wind is not spherically symmetric, but
exhibits a clearly elongated structure. Overall, the AMBER observations
confirm that the extremely high mass loss of Eta Carinae's massive central
star is non-spherical and much stronger along the poles than in the
equatorial plane. This is in agreement with theoretical models that
predict such an enhanced polar mass-loss in the case of rapidly rotating
stars.

Several papers from this special feature focus on the later stages in a
star's life. One looks at the binary system Gamma 2 Velorum, which
contains the closest example of a star known as a Wolf-Rayet. A single
AMBER observation allowed the astronomers to separate the spectra of the
two components, offering new insights in the modeling of Wolf-Rayet stars,
but made it also possible to measure the separation between the two stars.
This led to a new determination of the distance of the system, showing
that previous estimates were incorrect. The observations also revealed
information on the region where the winds from the two stars collide.

The famous binary system RS Ophiuchi, an example of a recurrent nova, was
observed just 5 days after it was discovered to be in outburst on 12
February 2006, an event that has been expected for 21 years. AMBER was
able to detect the extension of the expanding nova emission. These
observations show a complex geometry and kinematics, far from the simple
interpretation of a spherical fireball in extension. AMBER has detected a
high velocity jet probably perpendicular to the orbital plane of the
binary system, and allowed a precise and careful study of the wind and the
shockwave coming from the nova.

The stream of results from the VLTI and AMBER is no doubt going to
increase in the coming years with the availability of new functionalities.

"In addition to the 8.2-m Unit Telescopes, the VLTI can also combine the
light from up to 4 movable 1.8-m Auxiliary Telescopes. AMBER fed by three
of these AT's will be offered to the user community as of April this year,
and from October we will also make FINITO available," said Melnick. "This
'fringe-tracking' device allows us to stabilise changes in the atmospheric
conditions and thus to substantially improve the efficiency of the
observations. By effectively 'freezing' the interferometric fringes,
FINITO allows astronomers to significantly increase the exposure times."

The Astronomy & Astrophysics special feature (volume 464: March II 2007)
on AMBER first results includes 11 articles. They are freely available on
the A&A web site,
http://www.aanda.org/articles/aa/abs/2007/10/contents/contents.html

More Information

The AMBER consortium, led by Romain Petrov (Nice, France), includes
researchers from the Laboratoire d'Astrophysique de Grenoble (France),
Laboratoire d'Astrophysique Universitaire de Nice (France), Max-Planck
Institut für Radioastronomie (Bonn, Germany), INAF-Osservatorio
Astrofisico di Arcetri (Italy), and the Observatoire de la Côte d'Azur
(Nice, France).

In March 2004, the first on-line tests of AMBER (Astronomical Multiple
BEam Recombiner) were completed, when astronomers combined the two beams
of light from the southern star Theta Centauri from two test 40-cm
aperture telescopes (ESO 07/04). It was later used to combine light from
two, then three Unit Telescopes of ESO's VLT and light from the Auxiliary
Telescopes.

AMBER is part of the VLT Interferometer (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 four MACAO adaptive optics systems and the recent
arrival of the last of the four 1.8-m Auxiliary Telescopes at Paranal.

The principle of the interferometric technique is to combine the light
collected by two or more telescopes. The greater the distance between the
telescopes, the more details one can detect. For the VLTI, this distance
can be up to 200 metres, providing observers with milli-arcsecond spatial
resolution. With such a high spatial resolution, one would be able to
distinguish between the headlights of a car located on the Moon. In
addition, AMBER also provides astronomers with spectroscopic measurements,
allowing the structure and the physics of the source to be constrained by
comparing the measures at different wavelengths.

AMBER combines the light beams from three telescopes: this is a world
first 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 three baselines simultaneously 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.

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. The total shipping weight of the instrument and its extensive
associated electronics was almost 4 tons.

Two of the results discussed here were already presented as ESO press
releases in ESO 29/05 and 35/06.

National contacts for the media:

Belgium: Dr. Rodrigo Alvarez, +32-2-474 70 50
Finland: Ms. Riitta Tirronen, +358 9 7748 8369
Denmark: Dr. Michael Linden-Vørnle, +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, +39-357-230 26 51
The Netherlands: Ms. Marieke Baan, +31-20-525 74 80
Portugal: Prof. Teresa Lago, +351-22-089 833
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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