<title>FUEGOS: multifiber area spectrograph for one Nasmyth focus of the VLT</title>

Abstract

'FUEGOS' (Fibre Unit for European General Optical Spectroscopy) is one of the foreseen focal instruments for the future ESO VLT (very large telescope). The goal is to provide the european community with first class equipment allowing high and low resolution spectroscopy for stellar and extragalactic observations in a large field. This large field of view, 30 arcmin provided by the VLT, is quite unique on 8 m class telescopes. The instrument is made of two parts: a fibre positioner attached to the Nasmyth rotator and a spectrograph sitting on the Nasmyth platform. The two assemblies are linked together with optical fibres. The instrument will include two different modes: the MEDUSA mode for the multi-object spectroscopy and the ARGUS mode for the 2D spectroscopy for extended objects. The multi-object positioner is of the robot type, based on a design using two gripper heads travelling simultaneously on a X-Y carriage. It locks magnetically 80 independent optical fibre bundles at object coordinates on a metallic focal surface. 2D spectroscopy is provided through a fibre anamorphoser in three different fields and spatial samplings. The spectrograph is of the 'white pupil' type, based on a catadioptric design with spherical optics throughout. It gives access to spectral resolutions ranging from 1500 to 30000. The detector is a 2048 x 2048 CCD located inside the camera optics.