X-shooter, the new wide band intermediate resolution spectrograph at the ESO Very Large Telescope

J. Vernet¹, H. Dekker¹, S. D’Odorico¹, L. Kaper², P. Kjaergaard³, F. Hammer⁴, S. Randich⁵, F. Zerbi⁶, P. J. Groot⁷, J. Hjorth³, I. Guinouard⁴, R. Navarro⁸, T. Adolfse⁷, P. W. Albers⁷, J.-P. Amans⁴, J. J. Andersen³, M. I. Andersen³, P. Binetruy⁹, P. Bristow¹, R. Castillo¹⁰, F. Chemla⁴, L. Christensen¹¹, P. Conconi⁶, R. Conzelmann¹, J. Dam⁷, V. De Caprio¹², A. De Ugarte Postigo³, B. Delabre¹, P. Di Marcantonio¹³, M. Downing¹, E. Elswijk⁸, G. Finger¹, G. Fischer¹, H. Flores⁴, P. François⁴, P. Goldoni⁹, L. Guglielmi⁹, R. Haigron⁴, H. Hanenburg⁸, I. Hendriks⁷, M. Horrobin¹⁴, D. Horville⁴, N. C. Jessen¹⁵, F. Kerber¹, L. Kern¹, M. Kiekebusch¹, P. Kleszcz⁸, J. Klougart³, J. Kragt⁸, H. H. Larsen³, J.-L. Lizon¹, C. Lucuix¹, V. Mainieri¹, R. Manuputy¹⁶, C. Martayan¹⁰, E. Mason¹⁷, R. Mazzoleni⁶, N. Michaelsen³, A. Modigliani¹, S. Moehler¹, P. Møller¹, A. Norup Sørensen³, P. Nørregaard³, C. Péroux¹⁸, F. Patat¹, E. Pena¹⁰, J. Pragt⁸, C. Reinero¹⁰, F. Rigal⁸, M. Riva⁶, R. Roelfsema⁸, F. Royer⁴, G. Sacco¹⁹, P. Santin¹³, T. Schoenmaker⁸, P. Spano⁶, E. Sweers⁷, R. Ter Horst⁸, M. Tintori²⁰, N. Tromp⁸, P. van Dael⁷, H. van der Vliet⁷, L. Venema⁸, M. Vidali²¹, J. Vinther¹, P. Vola¹⁸, R. Winters⁷, D. Wistisen³, G. Wulterkens⁷ and A. Zacchei¹³

¹ European Southern Observatory, Karl Schwarzschild Strasse 2, 85748 Garching bei München, Germany
e-mail: jvernet@eso.org
² Astronomical Institute Anton Pannekoek, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
³ Niels Bohr Institute, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
⁴ GEPI – Observatoire de Paris, 5 place Jules Janssen, 92195 Meudon, France
⁵ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italia
⁶ INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy
⁷ Radboud Univ. Nijmegen, Postbus 9010, 6500 GL Nijmegen, The Netherlands
⁸ ASTRON, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherands
⁹ Laboratoire Astroparticule et Cosmologie, 10 rue A. Domon et L. Duquet, 75205 Paris Cedex 13, France
¹⁰ European Southern Observatory, Alonso de Córdova 3107 Vitacura, Casilla 19001, Santiago de Chile 19, Chile
¹¹ Excellence Universe Cluster, Technische Universität München, Bolzmannstr. 2, 85748 Garching bei München, Germany
¹² INAF – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
¹³ INAF – Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
¹⁴ Physikalisches Institut Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany
¹⁵ DTU Space, Juliane Maries vej 30, 2100 Copenhagen, Denmark
¹⁶ Technologie Centrum FNWI, Science Park 904, 1098 XH Amsterdam, The Netherlands
¹⁷ Space Telescope Science Institute, I3700 San Martin Drive, Baltimore, MD 21218, USA
¹⁸ Laboratoire d’Astrophysique de Marseille, OAMP, Université Aix-Marseille & CNRS, 38, rue Frédéric Joliot Curie, 13388 Marseille Cedex 13, France
¹⁹ Chester F. Carlson Center for Imaging Science, Rochester Institute of Technology, 54 Lomb Memorial Drive, 14623 Rochester, USA
²⁰ A.D.S. International S.r.l., via Roma 87, 23868 Valmadrera, Italy
²¹ EC JRC Institute for Reference Materials and Measurements, 2440 Geel, Belgium

Received: 21 July 2011
Accepted: 27 September 2011

Abstract

X-shooter is the first 2nd generation instrument of the ESO Very Large Telescope (VLT). It is a very efficient, single-target, intermediate-resolution spectrograph that was installed at the Cassegrain focus of UT2 in 2009. The instrument covers, in a single exposure, the spectral range from 300 to 2500 nm. It is designed to maximize the sensitivity in this spectral range through dichroic splitting in three arms with optimized optics, coatings, dispersive elements and detectors. It operates at intermediate spectral resolution (R ~ 4000−17 000, depending on wavelength and slit width) with fixed échelle spectral format (prism cross-dispersers) in the three arms. It includes a 1.8″ × 4″ integral field unit as an alternative to the 11′′ long slits. A dedicated data reduction package delivers fully calibrated two-dimensional and extracted spectra over the full wavelength range. We describe the main characteristics of the instrument and present its performance as measured during commissioning, science verification and the first months of science operations.