Happy anniversary, VLT!


Five years at the service of Europe's astronomers

One of the world's most advanced astronomical research facilities, the ESO Very Large Telescope (VLT) at the Paranal Observatory in the Chilean Atacama desert, celebrates an important anniversary today.

On April 1, 1999, and following almost one year of extensive tests and careful trimming of its numerous high-tech parts, the first 8.2-m VLT Unit Telescope, Antu (UT1), was "handed over" to the astronomers. Since that date, science operations with this marvellous research tool have been continuous and intensive. Kueyen (UT2) started normal operations exactly one year later. Yepun (UT4) was offered to the scientific community in June 2001, while Melipal (UT3) followed in August 2001 [1].

Ever since, all four VLT Unit Telescopes, with an ever-growing suite of highly specialised, extremely powerful astronomical instruments have been in full operation, 365 nights a year. And this with unequalled success, as demonstrated by a long list of important scientific results, including a substantial number of exciting discoveries that are now opening new horizons in astrophysics. Moreover, thanks to heroic and persistent efforts by the dedicated teams of ESO scientists and engineers, the "downtime" due to technical problems has been very small, about 3 per cent, a number that is unequalled among the world's large telescope facilities. In addition, the weather conditions at the Paranal site in the dry Atacama desert in Northern Chile are truly excellent - this is indeed one of the best locations for astronomical observations on the surface of the Earth - and the corresponding "weather downtime" has only been around 10 per cent. This has resulted in an unbelievably low value of total downtime, most likely a new world record for ground-based 8-10 m class telescopes.

VLT strong points

The Very Large Telescope (VLT) is the world's largest and most advanced optical telescope. It comprises four 8.2-m reflecting Unit Telescopes (UTs) and will in due time also include four moving 1.8-m Auxiliary Telescopes (ATs), the first one of which successfully passed its first tests in January of this year (see ESO PR 01/04).

With unprecedented optical resolution and unsurpassed surface area, the VLT produces extremely sharp images and can record light from the faintest and most remote objects in the Universe. It works at the limit of modern technology, regularly allowing the scientists to peer into new and unknown territories in the immense Universe.

Contrary to other large astronomical telescopes, the VLT was designed from the beginning with the use of interferometry as a major goal. For this reason, the four 8.2-m Unit Telescopes were positioned in a quasi-trapezoidal configuration. The light beams from these telescopes, at this moment two-by-two, can be combined in the VLT Interferometer (VLTI).

It provides the European scientific community with a ground-based telescope array with collecting power significantly greater than any other facilities available at present or being planned, offering imaging and spectroscopy capabilities at visible and infrared wavelengths.

Seven of the planned ten first-generation astronomical instruments are now in operation at the VLT. They cover all major observing modes required to tackle current "hot", front-line research topics:

    -the multi-mode instrument FORS1 (FOcal Reducer and Spectrograph) and its twin, FORS2,
    -the Infrared Spectrometer And Array Camera (ISAAC) cryogenic infrared imager and spectrometer,
    -the UVES (Ultra-violet and Visible Echelle Spectrograph) high-dispersion spectrograph,
    -the NAOS-CONICA Adaptive Optics facility producing images as sharp as if taken in space [2],
    -the VIsible Multi-Object Spectrograph (VIMOS) four-channel multiobject spectrograph and imager - allowing to obtain low-resolution spectra of up to 1000 galaxies at a time
    -the Fibre Large Array Multi-Element Spectrograph (FLAMES) that offers the unique capability to study simultaneously and at high spectral resolution 100 individual stars in nearby galaxies.

The remaining instruments - the high-resolution infrared spectrograph CRIRES, the Mid Infrared Spectrometer/Imager VISIR and the integral field spectrograph SINFONI - will be installed in 2004-2005.

The observational statistics prove that these instruments are extremely efficient - they have some of the highest "shutter-open times" (i.e. percentage of the maximum possible observing time during which the instruments are collecting light from the astronomical objects) ever achieved. The astronomers are well served in this respect: the ISAAC instrument, for example, continues to be in the highest demand and has now performed smoothly during more than 1000 nights and two others, UVES and FORS, are now approaching the same number.

Working together with astronomers and engineers at many research institutes in the ten ESO member countries, ESO is now in the process of defining second generation instruments and feasibility studies are well under way. Among the prime projects in this direction are a cryogenic multi-object spectrometer in the near-infrared 1 to 2.4 _m range ("KMOS"), a medium-resolution wide-band (0.32 to 2.4 _m) spectrometer ("X-shooter"), as well as a wide-field 3D optical spectrometer ("3D deep-field surveyor") and a high-contrast, adaptive optics assisted, imager ("planet finder").

In addition to these highly innovative instruments for the VLT UTs, specific instruments that will work with the combined light from several of the telescopes have also been conceived. The interferometric instrument MIDI will be offered to the astronomical community from today (April 1, 2004), fulfilling the VLTI promise. Great efforts have indeed gone into making observations with this very complex science machine as user-friendly as possible. 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.

Science with the VLT

The impressive battery of top-ranking instruments, coupled with the enormous light-collecting power of the VLT, has already provided a real research bonanza with many outstanding scientific results, some of which have been true breakthroughs. They include the amazing new knowledge about the Black Hole at the Galactic Centre, the farthest galaxy known, the most metal-poor and hence, oldest stars, accurate cosmochronological dating by means of Uranium and Thorium spectral lines, high-redshift galaxy rotation curves, micro-quasars, properties of the optical counterparts of gamma-ray bursts, high-redshift supernovae, etc. [3]. All of these advances attest to the power of the VLT and its mode of operational. Not to be forgotten is also the beauty of many of the stunning images obtained with this telescope, one of which was voted amongst the 10 most inspirational astronomical images of the past century [4]. Look at the numerous and detailed ESO Press Releases for more examples of research achievements from the VLT.

This trend is also apparent in the productivity of the telescopes. The number of research publications resulting from VLT work in top ranking astronomical journals is steadily increasing with a total close to 700, hereof 250 in 2003 alone. Moreover, research articles based on VLT data are in the mean quoted twice as often as the average.

The very high efficiency of the VLT "science machine" now generates huge amounts of data at a very high rate. These are stored in a permanent Science Archive Facility at ESO headquarters, which is jointly operated by ESO and the Space Telescope European Coordinating Facility (ST-ECF). From here, data are distributed daily to astronomers on DVDs and over the World Wide Web. The archive facility has been conceived and developed to enable astronomers to "mine" very efficiently the enormous volumes of data that is collected from the VLT. The archive now contains more than 1 million images or spectra taken by the four UTs with a total volume of about 50 Terabytes (50,000,000,000,000 bytes) of data. This corresponds to the content of about 25 million books of 1000 pages each; they would occupy more than 1000 kilometres of bookshelves!

Looking towards the future

Says Catherine Cesarsky, ESO Director General since 1999: " The Paranal Observatory has already given rise to an impressive number of scientific results, many of which could not have been obtained elsewhere. Overall, the VLT has been a most remarkable success, and will contribute to science at the highest level for years to come - a fantastic achievement of which we can all be justifiably proud."

The work is now underway at full power to provide second-generation instruments for the VLT, to add three more Auxiliary Telescopes to the VLTI and to complement this unique research facility with the two wide-field survey ("pathfinding") telescopes - one to work in the visible part of the spectrum (the 2.5-m VST), the other in the infrared (the 4-m VISTA) - now being constructed at Paranal.

Roberto Gilmozzi, director of Paranal Observatory, looks forward: " Ever more exciting times lie ahead for Paranal with new instruments like VISIR and SINFONI and the laser guide star, all of them coming this year. Five years after the start of operations on UT1, the observatory operates its telescopes with very little time set aside for engineering (less than 10%) and very low technical down time. Combined with excellent weather and great image quality, we provide the European community with unsurpassed observing capabilities. As director of this observatory since 1999, I have been privileged to be part of this adventure."

The VLT is a fine example of the vast benefits of pooling resources from several countries and it is a flagship of contemporary European research. There is little doubt that for many years to come, ESO's Paranal Observatory with its powerful and efficient facilities will continue to play a leading role in astronomical research.

Source: Eurekalert & others

Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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