GIRAFFE sees its first light

Paris, July 9, 2002

CNRS/Observatoire de Paris Joint Release

The GIRAFFE spectrograph has just obtained its first light at the Very Large Telescope of the European Southern Observatory (ESO). It is a multi-fiber spectrograph that will enable high-quality spectral observations to be made of a wide variety of celestial objects, ranging from the stars of the Milky Way to the most distant galaxies. The FLAMES (Fiber Large Array Multi-Element Spectrograph) facility includes the GIRAFFE spectrograph, the fiber systems, the OzPoz fiber positioner, and the field corrector. It has been developed through collaboration between the European Southern Observatory, the Observatoire de Paris, the Observatory of Geneva, and the Anglo Australian Observatory. The optical fiber systems and the GIRAFFE spectrograph were produced by the "Galaxies, Etoiles, Physique et Instrumentation" (Galaxies, Stars, Physics, and Instrumentation) Laboratory of the Observatoire de Paris or "GEPI", a CNRS joint research unit. Such an instrument will improve our understanding of the physics of the stars and of the evolution of the galaxies, which are the keystones of the construction of the Universe.

The principle of this instrument consists in positioning toward the sky a series of optical fibers, each of which serves to collect the light from a respective portion of sky. The area covered represents a field of vision that is 25 arc minutes across, i.e. equivalent to the size of the Moon. The light is channeled by the fibers to the one or more spectrographs that produce the spectra from it. The fibers are moved in the focal plane by a positioner.
The instrument has 4 observation modes. Two of the modes are of the simple "multi-object" type: each fiber serves to collect the light from a respective star (132 objects can be observed simultaneously). GIRAFFE offers unique possibilities for detailed study of the properties (age, abundance, rotation, radial velocity) of stars well beyond the solar environment, including stars located in the disk, the bulge, and the halo of the Milky Way (see spectrum in Figure 1 and detail of that spectrum in Figure 2), and also stars in other galaxies of the Local Group.

The other two modes are of the "3-D spectroscopy" or "integrated field" type. Their principle consists in subdividing an extended object (a galaxy) into a series of pixels, and in producing as many spectra from them. One of the specific features of GIRAFFE is that it is the first instrument in the world to deploy simultaneously 15 "integral field units" (IFUs), each of which is made up of a mosaic of 20 optical fibers that are positioned over the sky. Each of theses units resembles an insect's eye, and together they collect no less than 300 spectra simultaneously. On GIRAFFE, these pixels are defined by arrays of micro-lenses which feed strands of fibers.Under the responsibility of and with the support of the ESO, the fiber systems (including the IFUs) and the GIRAFFE spectrograph have been produced by the GEPI Laboratory of the Observatoire de Paris (CNRS joint research unit), the fiber positioner has been produced by the Anglo Australian Observatory, and the data reduction software has been developed by the Observatory of Geneva in collaboration with the GEPI Laboratory.

Researcher contact:
François Hammer
Observatoire de Paris
Tel: +33 1 45 07 74 08
e-mail: francois.hammer@obspm.fr
Véronique Cayatte
Observatoire de Paris
Tel: +33 1 45 07 74 24
e-mail: veronique.cayatte@obspm.fr

CNRS-INSU contact:
Philippe CHAUVIN
Tel: +33 1 44 96 43 36
e-mail: Philippe.Chauvin@cnrs-dir.fr

CNRS press contact::
Martine Hasler
Tel: +33 1 44 96 46 35
e-mail: martine.hasler@cnrs-dir.fr