11 The Messenger 123 – March 2006 Telescopes and Instrumentation The VLT Adaptive Optics Facility Project: Adaptive Optics Modules Robin Arsenault 1 Norbert Hubin 1 Stefan Stroebele 1 Enrico Fedrigo 1 Sylvain Oberti 1 Markus Kissler-Patig 1 Roland Bacon 6 Richard McDermid 7 Domenico Bonaccini-Calia 1 Roberto Biasi 3 Daniele Gallieni 4 Armando Riccardi 5 Rob Donaldson 1 Miska Lelouarn 1 Wolfgang Hackenberg 1 Ralf Conzelman 1 Bernard Delabre 1 Remko Stuik 7 Jerome Paufique 1 Markus Kasper 1 Elise Vernet 1 Mark Downing 1 Simone Esposito 5 Michel Duchateau 1 Marijn Franx 7 Richard Myers 2 Steven Goodsell 2 1 ESO 2 University of Durham, United Kingdom 3 MicroGate 4 ADS International 5 INAF – Osservatorio Astrofisico di Arcetri, Italy 6 CRAL, Observatoire de Lyon, France 7 Leiden University, the Netherlands The Adaptive Optics Facility is a project to convert UT4 into a specialised Adap- tive Telescope with the help of a De- formable Secondary Mirror (see previ- ous article). The two instruments that have been identified for the two Nas- myth foci are: Hawk-I with its AO mod- ule GRAAL allowing a Ground Layer Adaptive Optics correction (GLAO) and MUSE with GALACSI for GLAO correc- tion and Laser Tomography Adaptive Optics correction. This article describes the AO modules GRAAL and GALACSI and their Real-Time Computers based on SPARTA. Requirements for the instruments The three UT focal stations will benefit from the image correction provided by the Deformable Secondary Mirror (DSM). At the time of this writing two instruments are identified: Hawk-I and MUSE on the opposite Nasmyth foci. The correspond- ing AO modules are GRAAL (GRound layer Adaptive optics Assisted by Lasers) and GALACSI (Ground Atmospheric Lay- er Adaptive Corrector for Spectroscop- ic Imaging). The STC has requested ESO to propose options for the future use of the Cassegrain focus; in the meantime SINFONI will remain at this focal station and will be available on the AO Facility. The AO corrections to be provided are new: Ground Layer Correction (GLAO) and Laser Tomography (LTAO). The form- er consists in measuring the turbulence in four different directions outside the instrument FOV and to average it in or- der to provide a homogeneous image improvement across the instrument FOV. The latter compensates for the laser cone effect (not sampling all the turbu- lence seen on the astronomical target) and optimises high strehl correction on-axis; therefore, the need for four Laser Guide Stars. Figure 1 illustrates these correction modes. The present article details mainly the AO modules for Hawk-I and MUSE and the Real-Time-Computer platform SPARTA. Note that Hawk-I is an ESO-led effort. This instrument completed its Final Design Phase at the end of 2004 and is in the manufacturing stage. MUSE is an external consortium effort led by the Observatoire de Lyon (CRAL) including the University of Leiden, the Eidgenössische Technische Hochschule Zürich, Astrophysikalisches Institut Pots- dam, the Observatoire Midi-Pyrénées (LAOMP), and the Institut für Astrophysik Göttingen. Description of the AO Modules GRAAL for HAWK-I Concept The GRound layer Adaptive optics system Assisted by Lasers (GRAAL) is a mod- ule designed to provide GLAO correction for the HAWK-I NIR wide-field imager (7.5; × 7.5; FoV with ~ 0.1? pixels). GRAAL is designed as a module hosting four WFSs for LGS and a tip-tilt sensor for a NGS. The atmospheric turbulence is sampled in four slightly different direc- tions over the instrument field of view to Figure 1: Illustration of the Ground Layer adaptive correction (left) and Laser Tomography (right). Reference Stars Laser Guide Stars High Altitude Layer Ground Layer Ground Conj. DM WFC Camera Ground Layer AO Laser Tomography AO Telescope © E. Marchetti, ESO, 2005 WFS WFC