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12\18 ESO - New Vistas Open with MIDI at the VLT Interferometer
Part 1 of 4

             Information from the European Southern Observatory
 ESO Press Release 25/02
 18 December 2002                                         [ESO Logo]
 For immediate release
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New Vistas Open with MIDI at the VLT Interferometer

"First Fringes" in Mid-Infrared Spectral Region with Two Giant 
Telescopes [1]

Summary

Following several weeks of around-the-clock work, a team of
astronomers and engineers from Germany, the Netherlands, France and
ESO [2] has successfully performed the first observations with the
MID-Infrared interferometric instrument (MIDI), a new, extremely
powerful instrument just installed in the underground laboratory of
the VLT Interferometer (VLTI) at the Paranal Observatory (Chile).

In the early morning of December 15, 2002, two of the 8.2 m VLT unit
telescopes (ANTU and MELIPAL) were pointed towards the southern star
Epsilon Carinae and the two light beams were directed via the complex
intervening optics system towards MIDI. After a few hours of tuning
and optimization, strong and stable interferometric fringes were
obtained, indicating that all VLTI components - from telescopes to the
new instrument - were working together perfectly. Two more stars were
observed before sunrise, further proving the stability of the entire
system.

The first observations with MIDI mark one more important step towards
full and regular operation of the VLT Interferometer [3]. They are a
result of five years of determined efforts within a concerted
technology project, based on a close collaboration between ESO and
several European research institutes (see below). Now opening great
research vistas, they also represent several "firsts" in observational
astrophysics, together amounting to a real breakthrough in the field
of astronomical interferometry.

New views at mid-infrared wavelengths: MIDI is sensitive to light of a
wavelength near 10 micron, i.e., in the mid-infrared spectral region
("thermal infrared"). This provides rich opportunities to study a wide
range of otherwise inaccessible, crucial astrophysical phenomena,
e.g., the formation of planets in dusty disks around newborn stars and
the innermost regions around black holes.

However, it is a great technical challenge to perform mid-IR
observations.  This is first of all because the terrestrial
atmosphere, the telescopes, their mounts and, not least, the
complicated optics system needed to guide the beams the long way from
the telescopes to the MIDI instrument all glow bright at mid-IR
wavelengths. Thus, even the most luminous mid-IR stellar sources
"drown" in this bright background, calling for highly refined
observational methods and data reduction procedures.

Fainter objects with large telescopes: This is the first time
telescopes with mirrors as large as these have been used for mid-IR
interferometry.  The use of the VLT giants at Paranal now allows
observing much fainter objects than before.

Sharper images with Interferometry: The distance between ANTU and
MELIPAL during these observations, 102 metres, is a new world record
for interferometry at this wavelength. The achieved angular resolution
is indeed the one theoretically possible with this instrumental
configuration, about 0.01 arcsec, better than what has ever been
achieved before from ground or space at this wavelength.

MIDI is the first of two instruments that will be placed at the focus 
of the VLT Interferometer. It is a collaborative project between 
several European research institutes:

* European Southern Observatory (ESO)

* Max Planck Institut fuer Astronomie (MPIA) (Heidelberg, Germany)

* Netherlands Graduate School for Astronomy (NOVA) (Leiden, The
  Netherlands)

* Department of Astronomy - Leiden Observatory (The Netherlands)

* Kapteyn Astronomical Institute (Groningen, The Netherlands)

* Astronomical Institute, Utrecht University (The Netherlands)

* Netherlands Foundation for Research in Astronomy (NFRA) 
  (Dwingeloo, The Netherlands)

* Space Research Organization Netherlands (SRON) (Utrecht, 
  Groningen; The Netherlands)

* Thueringer Landessternwarte Tautenburg (TLS) (Germany)

* Kiepenheuer-Institut fuer Sonnenphysik (KIS) (Freiburg, Germany)

* Observatoire de Paris (OBSPM) (Paris, Meudon, Nancay; France)

* Observatoire de la Cote d'Azur (OCA) (Nice, France)

The first observations with MIDI will now be followed up by thorough
tests of the new instrument before it enters into regular service. It
is planned that the first community observations will be performed at
the VLTI in mid-2003. Great efforts have gone into making observations
with this complex science machine as user-friendly as possible and,
contrary to what is normally the case in this technically demanding
branch of astronomy, scientists will find interferometric work at the
VLTI quite similar to that of using the many other, more conventional
VLT instruments.

A wonderful moment
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[PR Photo 30a/02 - PR Video Clip 03/02 - PR Photo 30b/02]

Captions: PR Photo 30a/02 shows the "first fringes" of the star
Epsilon Carinae, as obtained at VLTI with the new MIDI instrument at
the mid-infrared wavelength of 8.7 micron. PR Video Clip 03/02 shows
the signature of the interference fringes, as they appear on the
computer screen when the optical path difference between the two arms
of the interferometer is slowly varied. From left to right, the
complex system of the VLTI delay lines changes this difference over a
length of about 1 mm (or 1/200,000 of the total path length of about
200 metres!). At each intermediate position, the MIDI instrument scans
the signal for the presence of fringes, by means of a digital
filtering algorithm. At the scan position in which fringes are
present, the signal increases dramatically: this is therefore the
position at which the light beams from ANTU and MELIPAL travel exactly
the same distance. PR Photo 30b/02 is a photo of the group responsible
for the MIDI installation and first tests, taken inside the VLT
Control Building, right after the successful "First Fringes" in the
early morning of December 15. From left to right: Front row
(sitting/kneeling) Julio Navarette, Lorena Faundez, Markus Schoeller,
Andrea Richichi - Back row (standing) Francesco Paresce, Andres Pino,
Uwe Gaser, Olivier Chesneau, Christoph Leinert, Andreas Glindeman,
Walter Jaffe, Sebastian Morel, Richard Mathar, Pierre Kervella, Eric
Bakker.

Another vital step has been accomplished as planned towards full
operation of the ESO Very Large Telescope (VLT) and the associated VLT
Interferometer (VLTI) at the Paranal Observatory in Chile, one of the
world's foremost astronomical facilities. Indeed, plans had been made
more than one year ago for this milestone event to take place at the
end of 2002.

(continued)

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