Press Release

Multiple Eyes for the VLT [1]

By SpaceRef Editor
January 28, 2002
Filed under ,

First System of Deployable Multi-Integral Field Units Ready


Summary

  • Images


    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 Caption: PR Photo 03a/02: The 03a/02 GIRAFFE spectrograph, a major component of the VLT Fibre Large Array Multi-Element Spectrograph [Preview - JPEG: 560 x 400 pix - (FLAMES), during the present 62k] assembly at the ESO Headquarters in [Normal - JPEG: 1120 x 800 pix - Garching (Germany). 544k] [Hi-Res - JPEG: 2885 x 2061 pix - 5.3M]


    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   [ESO PR Photo 03c/02]  ESO PR Photo
                             03b/02                                03c/02
    
     [Preview - JPEG: 573 x 400 pix -      [Preview - JPEG: 538 x 400 pix -
     94k]                                  63k]
     [Normal - JPEG: 1145 x 800 pix -      [Normal - JPEG: 1076 x 800 pix -
     592k]                                 256k]
    
    

    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  Caption: PR Photo 03d/02: Mechanical
                             03d/02        design of an IFU "button". Upper
                                           right: photo of an "IFU entrance"
                                           with the 20 square microlenses, each
     [Preview - JPEG: 400 x 469 pix -      measuring 1.8 x 1.8 mm^2.
     86k]
     [Normal - JPEG: 800 x 937 pix -
     232k]
    


    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 Positioner.


    A magnet is incorporated at the base of the button to ensure a stable
    position (a firm hold) on the focal plate during the observation. The
    optical cementing is ensured with an UV curing and the fibre bundle is
    cemented into the button with an epoxy glue in order to ensure excellent
    stiffness of the complete assembly. The external diameter of the button is
    about 6 mm, corresponding to about 11 arcsec on the sky, allowing quite
    close positioning of the buttons on the focal plate.


    An example of astronomical observations with IFUs

      [ESO PR Photo 03e/02]  ESO PR Photo  Caption: PR Photo 03e/02 is a
                             03e/02        computer simulation of the velocity
                                           field in a galaxy, as deduced on the
                                           basis of IFU spectra. The blue area
     [Preview - JPEG: 467 x 400 pix -      has negative velocities and is thus
     51k]                                  the approaching side of the galaxy,
     [Normal - JPEG: 933 x 800 pix -       while the red area is receding. In
     264k]                                 this way, the direction of rotation
                                           can be determined. The velocity unit
                                           is km/s.
    


    During the astronomical observation with the IFUs, the spectrograph slit
    receives light from 15 sky areas simultaneously, each with 21 fibres (20
    from the IFU and 1 that collects the light from the night sky in an adjacent
    sky field) or 22 fibres (with the addition of 1 fibre with light from a
    calibration lamp). Altogether, about 300 spectra are recorded
    simultaneously.


    By means of such observations, the astronomers can perform many different
    studies, e.g., of the dynamics of star clusters and motions of stars and
    interstellar clouds in galaxies.


    PR Photo 03e/02 provides an example of a computer simulation of a resulting
    diagramme in which the internal rotation of a distant spiral galaxy is
    clearly visible. Red and yellow areas have positive velocities that are
    approaching while the blue areas are receding). Of special interest will be
    the study of the often violent motions when two or more galaxies interact
    gravitationally.


    Notes


    [1]: This is a joint Press Release of ESO and the Observatoire de Paris (cf.
    http://www.obspm.fr/actual/).


    [2]:The GIRAFFE team at the Observatoire de Paris that has developed the
    Integral Field Units (IFUs) discussed in this Press Release includes
    Jean-Pierre Aoustin, Sebastien Baratchart, Patrice Barroso, Veronique
    Cayatte, Laurent Chemin, Florence Cornu, Jean Cretenet, Jean-Paul Danton,
    Hector Flores, Francoise Gex, Fabien Guillon, Isabelle Guinouard, Francois
    Hammer, Jacques Hammes, David Horville, Jean-Michel Huet, Laurent Jocou,
    Pierre Kerlirzin, Serge Lebourg, Hugo Lenoir, Claude Lesqueren, Regis
    Marichal, Michel Marteaud, Thierry Melse, Fabrice Peltier, Francois Rigaud,
    Frederic Sayede and Pascal Vola.


    [3]: It is expected to ship the various components of the FLAMES instrument
    to the VLT Observatory at Paranal (Chile) during the next month. “First
    Light” is scheduled to take place some weeks thereafter, following
    installation at the telescope and extensive system tests. ESO will issue
    another Press Release with more details on that occasion.


    Contacts


    Francois Hammer
    Observatoire de Paris-Meudon
    Meudon, France
    Tel.: +33 1 45 07 74 08
    email: francois.hammer@obspm.fr


    Gerardo Avila
    European Southern Observatory
    Garching, Germany
    Tel.: +4989-3200-6394
    email: gavila@eso.org

  • SpaceRef staff editor.