Mathematics – Logic
Scientific paper
Mar 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005eso..pres....6.&link_type=abstract
ESO Press Release, 03/2005
Mathematics
Logic
Scientific paper
World's Largest Interferometer with Moving Optical Telescopes on Track
Summary
The Very Large Telescope Interferometer (VLTI) at Paranal Observatory has just seen another extension of its already impressive capabilities by combining interferometrically the light from two relocatable 1.8-m Auxiliary Telescopes.
Following the installation of the first Auxiliary Telescope (AT) in January 2004 (see ESO PR 01/04), the second AT arrived at the VLT platform by the end of 2004. Shortly thereafter, during the night of February 2 to 3, 2005, the two high-tech telescopes teamed up and quickly succeeded in performing interferometric observations.
This achievement heralds an era of new scientific discoveries. Both Auxiliary Telescopes will be offered from October 1, 2005 to the community of astronomers for routine observations, together with the MIDI instrument.
By the end of 2006, Paranal will be home to four operational ATs that may be placed at 30 different positions and thus be combined in a very large number of ways ("baselines"). This will enable the VLTI to operate with enormous flexibility and, in particular, to obtain extremely detailed (sharp) images of celestial objects - ultimately with a resolution that corresponds to detecting an astronaut on the Moon.
PR Photo 07a/05: Paranal Observing Platform with AT1 and AT2 PR Photo 07b/05: AT1 and AT2 with Open Domes PR Photo 07c/05: Evening at Paranal with AT1 and AT2 PR Photo 07d/05: AT1 and AT2 under the Southern Sky PR Photo 07e/05: First Fringes with AT1 and AT2 PR Video Clip 01/05: Two ATs at Paranal (Extract from ESO Newsreel 15)
A Most Advanced Device
ESO PR Video 01/05
ESO PR Video 01/05
Two Auxiliary Telescopes at Paranal
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ESO PR Photo 07a/05
ESO PR Photo 07a/05
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Captions: ESO PR Video Clip 01/05 is an extract from ESO Video Newsreel 15, released on March 14, 2005. It provides an introduction to the VLT Interferometer (VLTI) and the two Auxiliary Telescopes (ATs) now installed at Paranal. ESO PR Photo 07a/05 shows the impressive ensemble at the summit of Paranal. From left to right, the enclosure of VLT Antu, Kueyen and Melipal, AT1, the VLT Survey Telescope (VST) in the background, AT2 and VLT Yepun.
Located at the summit of the 2,600-m high Cerro Paranal in the Atacama Desert (Chile), ESO's Very Large Telescope (VLT) is at the forefront of astronomical technology and is one of the premier facilities in the world for optical and near-infrared observations.
The VLT is composed of four 8.2-m Unit Telescope (Antu, Kueyen, Melipal and Yepun). They have been progressively put into service together with a vast suite of the most advanced astronomical instruments and are operated every night in the year.
Contrary to other large astronomical telescopes, the VLT was designed from the beginning with the use of interferometry as a major goal. The href="/instruments/vlti">VLT Interferometer (VLTI) combines starlight captured by two 8.2- VLT Unit Telescopes, dramatically increasing the spatial resolution and showing fine details of a large variety of celestial objects.
The VLTI is arguably the world's most advanced optical device of this type. It has already demonstrated its powerful capabilities by addressing several key scientific issues, such as determining the size and the shape of a variety of stars (ESO PR 22/02, PR 14/03 and PR 31/03), measuring distances to stars (ESO PR 25/04), probing the innermost regions of the proto-planetary discs around young stars (ESO PR 27/04) or making the first detection by infrared interferometry of an extragalactic object (ESO PR 17/03). "Little Brothers"
ESO PR Photo 07b/05
ESO PR Photo 07b/05
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ESO PR Photo 07c/05
ESO PR Photo 07c/05
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ESO PR Photo 07d/05
ESO PR Photo 07d/05
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Captions: ESO PR Photo 07b/05 shows VLTI Auxiliary Telescopes 1 and 2 (AT1 and AT2) in the early evening light, with the spherical domes opened and ready for observations. In ESO PR Photo 07c/05, the same scene is repeated later in the evening, with three of the large telescope enclosures in the background. This photo and ESO PR Photo 07c/05 which is a time-exposure with AT1 and AT2 under the beautiful night sky with the southern Milky Way band were obtained by ESO staff member Frédéric Gomté.
However, most of the time the large telescopes are used for other research purposes. They are therefore only available for interferometric observations during a limited number of nights every year. Thus, in order to exploit the VLTI each night and to achieve the full potential of this unique setup, some other (smaller), dedicated telescopes were included into the overall VLT concept.
These telescopes, known as the VLTI Auxiliary Telescopes (ATs), are mounted on tracks and can be placed at precisely defined "parking" observing positions on the observatory platform. From these positions, their light beams are fed into the same common focal point via a complex system of reflecting mirrors mounted in an underground system of tunnels.
The Auxiliary Telescopes are real technological jewels. They are placed in ultra-compact enclosures, complete with all necessary electronics, an air conditioning system and cooling liquid for thermal control, compressed air for enclosure seals, a hydraulic plant for opening the dome shells, etc. Each AT is also fitted with a transporter that lifts the telescope and relocates it from one station to another. It moves around with its own housing on the top of Paranal, almost like a snail.
Moreover, these moving ultra-high precision telescopes, each weighing 33 tonnes, fulfill very stringent mechanical stability requirements: "The telescopes are unique in the world", says Bertrand Koehler, the VLTI AT Project Manager. "After being relocated to a new position, the telescope is repositioned to a precision better than one tenth of a millimetre - that is, the size of a human hair! The image of the star is stabilized to better than thirty milli-arcsec - this is how we would see an object of the same size as one of the VLT enclosures on the Moon. Finally, the path followed by the light inside the telescope after bouncing on ten mirrors is stable to better than a few nanometres, which is the size of about one hundred atoms."
A World Premiere
ESO PR Photo 07e/05
ESO PR Photo 07e/05
"First Fringes" with two ATs
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Caption: ESO PR Photo 07e/05 The "First Fringes" obtained with the first two VLTI Auxiliary Telescopes, as seen on the computer screen during the observation. The fringe pattern arises when the light beams from the two 1.8-m telescopes are brought together inside the VINCI instrument. The pattern itself contains information about the angular extension of the observed object, here the 6th-magnitude star HD62082. The fringes are acquired by moving a mirror back and forth around the position of equal path length for the two telescopes. One such scan can be seen in the third row window. This pattern results from the raw interferometric signals (the last two rows) after calibration and filtering using the photometric signals (the 4th and 5th row). The first two rows show the spectrum of the fringe pattern signal. More details about the interpretation of this pattern is given in Appendix A of PR 06/01.
The possibility to move the ATs around and thus to perform observations with a large number of different telescope configurations ensures a great degree of flexibility, unique for an optical interferometric installation of this size and crucial for its exceptional performance. The ATs
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