Delivery of GIRAFFE : multi-fibers spectrograph for the VLT

The Observatoire de Paris just sent to ESO at Garching the GIRAFFE spectrograph. GIRAFFE is a multi-fiber spectrograph working at intermediate resolution from R=5000 to R=25000. GIRAFFE will be settled at the focus of the second VLT unit, KUEYEN, to be operated from Spring 2002. The combination of GIRAFFE and of the OzPoz fiber positioner is called FLAMES. It will be unique for studying detailed properties (ages, abundances, rotation etc...) of individual stars well beyond the solar environment, including stars located in the bulge and halo of the Milky Way and as far as those resolved in the Local Group galaxies. With GIRAFFE, we will know precisely the way dwarf galaxies have formed their heavy elements. GIRAFFE will provide at the same time 132 stellar spectra in its MEDUSA mode. It will also be the best instrument to resolve the velocity fields and the rotation curves of galaxies having emitted their lights 8 to 9 Gyr ago. In its multi-integral field mode, GIRAFFE will allow the observation of 15 such galaxies at the same time, each of them being spatially resolved by 20 optical fibers. This will provide new insights on our understanding on how galaxies were assembling together in the early Universe. For each mode, several additional fibers are devoted to sky subtraction and to simultaneous calibration. Observatoire de Paris has originated the concept of a multi-mode and multi-object spectrograph using optical fibers and is the major contributor of the GIRAFFE development. Besides the full development and supply of the whole set of fibers (equivalent to about 1500 monofibers), of the instrument simulator and of the data reduction software of the 3D modes, the Observatoire de Paris team (1) has provided the whole concept and manufacturing of the electro-mechanics of the spectrograph. Here is a view of this instrument assembled at ESO (2) :GIRAFFE has a quite simple optical design where all the components are aligned. The mechanical architecture is then composed of only 5 sub-assemblies :1- The structure and its enclosure are designed to offer a high thermo-mechanical stability and to resist to earthquake accelerations.2- The Spectrograph Entrance Assembly groups in a relative small volume five of the main functions of spectrograph : the fibre slit selection, the refocusing, the filter selection (the spectrograph has thirty filters), the back-illumination of the fibres during the positionning and the possibility to uniformly light the spectrograph entrance for daytime calibration. 3- The grating unit is mainly a turret allowing simultaneously the choice of the grating (HR or LR) and the selection of orders. Its design is quite simple -a couple of ball bearings supports directly on its axis a torque motor, a tachometer and an encoder- but all the components of the system are of very high quality and accuracy. The first tests give a repeatability in positioning lower than one arcsec.4 & 5- The collimator and the camera assemblies are (shutter excluded) passive supports of the main optics. These optics are manufactured by SODERN at Limeil-Brevannes. The supports and adjusting systems are provided by Observatoire de Paris.In addition to these five assemblies a sixth one, the calibration box, allows the capability to illuminate via an integrating sphere 5 fibres of each slit. This system, materially positionned outside the spectrograph, offers the originality of a simultaneous wavelength calibration of exposures. The first assembly of this box is in progress.GIRAFFE development has been put on a "fast-track" since the signature of the contract in January 1999. The Observatoire de Paris contribution corresponds to more than 35 man-years. In the following weeks the integration will continue in Munich by the installation of the final control electronics, the control software and a set of dummy fibres for the tests. (1) Giraffe Team at OP : F. Hammer (PI), J-P. Aoustin, S. Baratchart, P. Barroso, V. Cayatte, F. Cornu, J.Crétenet, S. Croce, J-P. Danton, F. Gex, I. Guinouard, P. Habault, J. Hammès, L. Jocou, D. Horville, J-M. Huet, S. Lebourg, P. Kerlirzin, C. Lesqueren, R. Marichal, M. Marteaud, T. Melse, F. Rigaud, F. Sayède, P. Surcouf, P. Vola. (2) In charge at ESO : L. Pasquini (Science Resp.), H. Dekker (Project Manager). Contact : François Hammer (DAEC-GEPI, Observatoire de Paris-Meudon) Pascal Vola (DAEC-GEPI, Observatoire de Paris-Meudon) 

Dernière modification le 4 mars 2013