Mathematics – Logic
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002eso..pres....1.&link_type=abstract
ESO Press Release, 01/2002
Mathematics
Logic
Scientific paper
First System of Deployable Multi-Integral Field Units Ready
Summary
The ESO Very Large Telescope (VLT) at the Paranal Observatory is being equipped with many state-of-the-art astronomical instruments that will allow observations in a large number of different modes and wavebands.
Soon to come is the Fibre Large Array Multi-Element Spectrograph (FLAMES) , a project co-ordinated by ESO. It incorporates several complex components, now being constructed at various research institutions in Europe and Australia.
One of these, a true technological feat, is a unique system of 15 deployable fibre bundles, the so-called Integral Field Units (IFUs) . They can be accurately positioned within a sky field-of-view measuring no less that 25 arcmin in diameter, i.e., almost as large as the full Moon . Each of the IFUs looks like an insect's eye and images a small sky area (3 x 2 arcsec 2 ) with a multiple microlens. From each IFU, 20 narrow light beams are sent via optical fibres to an advanced spectrograph. All 300 spectra are recorded simultaneously by a sensitive digital camera.
A major advantage of this technique is that, contrary usual spectroscopic observations in which spectral information is obtained along a (one-dimensional) line on the sky, it now allows (two-dimensional) area spectroscopy . This will permit extremely efficient spectral observations of many celestial objects, including faint galaxies, providing detailed information about their internal structure and motions. Such studies will have an important impact on our understanding, e.g., of the early evolution of galaxies , the main building blocks in the Universe.
The IFUs have been developed by a team of astronomers and engineers [2] at the Observatoire de Paris-Meudon. All IFU components are now at the ESO Headquarters in Garching (Germany) where they are being checked and integrated into the instrument [3].
PR Photo 03a/02 : The GIRAFFE spectrograph in the ESO Assembly Hall (Garching, Germany) . PR Photo 03b/02 : Example of a future IFU observation in a sky field with galaxies. PR Photo 03c/02 : An illustration of how the IFUs function . PR Photo 03d/02 : The IFU design . PR Photo 03e/02 : Computer simulation of the motions in a galaxy , as deduced from IFU observations. The FLAMES instrument and its many parts
ESO PR Photo 03a/02
ESO PR Photo 03a/02
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Caption : PR Photo 03a/02 : The GIRAFFE spectrograph, a major component of the VLT Fibre Large Array Multi-Element Spectrograph (FLAMES) , during the present assembly at the ESO Headquarters in Garching (Germany).
Late last year, the ESO Very Large Telescope (VLT) at the Paranal Observatory received its newest instrument, NAOS-CONICA . The first tests were very successful, cf. PR 25/01.
But this is far from the last. Work is now underway at several European and overseas research institutes to complete the many other large astronomical instruments planned for the VLT. Over the next years, these new facilities will enter into operation one by one, further enhancing the capabilities of this true flagship of European science.
One of these instruments is the Fibre Large Array Multi-Element Spectrograph (FLAMES) , to be installed at the 8.2-m VLT KUEYEN Unit Telescope. It will be able to observe the spectra of a large number of individual, faint objects (or small sky areas) simultaneously and incorporates several highly complex components, e.g.,
* a Nasmyth Corrector - an optical system to focus the light that is received from the telescope over a sky field of no less than 25 arcmin in diameter, i.e., almost as large as the full Moon . It was installed on KUEYEN in September 2001
* a Fibre Positioner (known as "OzPoz"). It is now being built by the AUSTRALIS Consortium, lead by the Anglo Australian Observatory (AAO) , cf. ESO PR 07/98
* a high- and intermediate-resolution optical spectrograph, GIRAFFE , with its own fibre system, developed by the Observatoire de Paris-Meudon in close collaboration with ESO . It is now in the process of being assembled in the ESO laboratories in Garching, cf. PR Photo 03a/01 .
Work at the FLAMES facility will be supported by specialized data reduction software developed by Observatoire de Genève-Lausanne in collaboration with Observatoire de Paris-Meudon , and specialized observing software developed at ESO . There will also be a fibre link to the UVES high-dispersion spectrograph and there are plans for incorporating an intermediate resolution IR spectrograph in the future; the ITAL-FLAMES consortium is now preparing the associated instrument control and data reduction software packages. The Integral Field Units (IFUs) for FLAMES
ESO PR Photo 03b/02
ESO PR Photo 03b/02
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ESO PR Photo 03c/02
ESO PR Photo 03c/02
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Caption : PR Photo 03b/02 : An example of observations with Integral Field Units (IFUs) at FLAMES (only 4 of the 15 units are shown here). Each IFU is placed so that it records the light from 20 small adjacent sky areas (each measuring about 3 x 2 arcsec 2 ). In this way, it is possible to register simultaneously the spectrum of as many different regions of a (distant) galaxy. PR Photo 03c/02 : How the IFUs work: each IFU consists of a microlens that guides the light from a small sky area, normally centred on a celestial object (e.g., a distant galaxy) and sends it on to the entry of the spectrograph (inside the dotted box).
When it enters into operation later this year [3], GIRAFFE will become the most efficient instrument of its kind available at the world's large optical/infrared telescopes. It will be especially suited for the study of the dynamical properties of distant galaxies - their motion in space, as well as the internal motions of their stars and gas clouds. Indeed, observations of the velocity fields in a large variety of galaxies in the early Universe (when its age was only one third to one half of its current age) will be essential for a better understanding of those major building blocks of the Universe.
This is first of all due to the unique system of 15 deployable fibre bundles, the Integral Field Units (IFUs) , that can be accurately positioned within a field-of-view measuring no less than 25 arcmin across, cf. PR Photo 03b/02 . Each IFU is a microscopic, state-of-the-art two-dimensional lens array with an aperture of 3 x 2 arcsec 2 on the sky. It contains twenty micro-lenses coupled with optical fibres leading the light recorded at each point in the field to the entry slit of the spectrograph, cf. PR Photo 03c/02 .
A great advantage of this technique is that, contrary to usual spectroscopic observations in which spectral information is obtained along a (one-dimensional) line on the sky, it now allows (two-dimensional) area spectroscopy . It is therefore possible to obtain spectra of larger areas of a celestial object simultaneously, and not just along one particular diameter.
With 15 IFUs at their disposal, the astronomers will be able to observe many galaxies at the same time - this will represent a tremendous gain of efficiency with many more astrophysical data collected within the available observation time! The IFU design
ESO PR Photo 03d/02
ESO PR Photo 03d/02
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Caption : PR Photo 03d/02 : Mechanical design of an IFU "button". Upper right: photo of an "IFU entrance" with the 20 square microlenses, each measuring 1.8 x 1.8 mm 2.
PR Photo 03d/02 shows the mechanical design of the entrance of one IFU. An array of 20 square microlenses, each measuring 1.8 x 1.8 mm 2 is used to concentrate the light in the corresponding, small sky field onto a prism that passes the light on to 20 fibres. These are inserted and cemented into a mechanical holder and the entire assembly is then mounted in an IFU "button" that will be positioned in the focal plane by the OzPoz Position
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