Calibration issues for MUSE Andreas Kelz* a , Martin Roth a , Svend Bauer a , Joris Gerssen a , Thomas Hahn a , Peter Weilbacher a , Uwe Laux c , Magali Loupias b , Johan Kosmalski b , Richard McDermid d , Roland Bacon b a Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany b Centre de Recherche Astronomique de Lyon, 9, Av. Charles André, 69230 St Genis-Laval, France c Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany d Universiteit Leiden, P.O. Box 9513 NL-2300 RA Leiden, The Netherlands ABSTRACT The Multi-Unit Spectroscopic Explorer (MUSE) is an integral-field spectrograph for the VLT for the next decade. Using an innovative field-splitting and slicing design, combined with an assembly of 24 spectrographs, MUSE will provide some 90,000 spectra in one exposure, which cover a simultaneous spectral range from 465 to 930nm. The design and manufacture of the Calibration Unit, the alignment tests of the Spectrograph and Detector sub-systems, and the development of the Data Reduction Software for MUSE are work-packages under the responsibility of the AIP, who is a partner in a European-wide consortium of 6 institutes and ESO, that is led by the Centre de Recherche Astronomique de Lyon. MUSE will be operated and therefore has to be calibrated in a variety of modes, which include seeing-limited and AO-assisted operations, providing a wide and narrow-field-of-view. MUSE aims to obtain unprecedented ultra-deep 3D- spectroscopic exposures, involving integration times of the order of 80 hours at the VLT. To achieve the corresponding science goals, instrumental stability, accurate calibration and adequate data reduction tools are needed. The paper describes the status at PDR of the AIP related work-packages, in particular with respect to the spatial, spectral, image quality, and geometrical calibration and related data reduction aspects. Keywords: 2D-spectroscopy, calibration, integral-field spectroscopy, optical design and manufacturing 1. INTRODUCTION The Multi-Unit Spectroscopic Explorer (MUSE) is one of the 2 nd generation VLT instruments [1, 2]. It is currently in the design phase, having passed the preliminary design review (PDR) at ESO in July 2007. The Astrophysical Institute Potsdam (AIP) is a partner in a European-wide consortium of 6 institutes and ESO, which is led by the Centre de Recherche Astronomique de Lyon (CRAL, P.I. R. Bacon). The AIP work-packages include the design and manufacture of the Calibration Unit [3], the alignment and testing of the Spectrograph and Detector sub-systems, and the development of the Data Reduction Software tools [4] for MUSE. These R&D tasks as well as pre-MUSE science and training activities among the German consortium partners are funded by the D3D-network [5], which is supported through the Verbundforschung by the German ministry for education and research BMBF. 1.1 A brief overview of MUSE Using an innovative field-splitting and slicing design, combined with an assembly of 24 identical spectrographs, MUSE will provide some 90,000 spectra in one exposure. The simultaneous wavelength range is from 480 to 930 nm nominally, which can be extended to 465 nm in the blue. The according resolving powers λ/∆λ of the fixed spectrograph setups range from 1750 at 465nm to 3750 at 930nm. MUSE offers a restricted variety of operational modes. In addition to the standard wide-field mode, a special narrow-field mode allows AO-assisted high-spatial resolution observations. The wide-field covers 1 x 1 arcmin 2 , which is sampled with 0.2 arcsec 2 , while the narrow-field mode has a spatial sampling of 25 x 25 milliarcsec 2 , resulting in a field of view of 7.5 x 7.5 arcsec 2 . The fore-optics features an image de-rotator, atmospheric dispersion compensator, shutter and provides anamorphic magnification of the field. The splitting and relay optics splits the science field into 24 sub-fields, that feed as many spectrograph units [6]. An assembly of image slicer, * send correspondence to: akelz@aip.de; fax +49 331 7499-429 Ground-based and Airborne Instrumentation for Astronomy II, edited by Ian S. McLean, Mark M. Casali, Proc. of SPIE Vol. 7014, 701458, (2008) · 0277-786X/08/$18 · doi: 10.1117/12.789407 Proc. of SPIE Vol. 7014 701458-1 2008 SPIE Digital Library -- Subscriber Archive Copy