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The MUSE instrument project
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Technical challenges
In contrast to classical spectrographs which provide a spectral information of one spatial
direction, an integral field spectrograph is designed to give a spectral information of a two
dimensional field of view. In order to preferably have a wide field of view, MUSE uses 24
integral field spectrographs that allow to observe an area of 1 x 1 arcmin². Each unit is
equipped with its own cryogenically cooled CCD head accommodating a detector with a
size of 4096x4096 pixels of 15 microns.
The VLT secondary mirror is equipped with more than one thousand actuators to remove
the distortion due to the atmosphere in real time. Therefore four artificial stars are created
by the smaller auxiliary telescopes, to have a reference. This system is part of the VLT
adaptive optics facility, developed separately from MUSE, by ESO.
The light gathered by the 8.2m mirror is focused on a field splitter and separator by the
adaptive secondary mirror, resulting in 24 different light paths that are directed to each
integral field unit (IFU). Within each IFU the field of view is again spilt into 48 slices by
the image slicer and finally a detector records the light signal, that has been dispersed by a
spectrograph. Each exposure taken by MUSE will have all in all 370 millions of pixels.
ESO is in charge of delivering 24 detector systems, that fulfil the high technological
requirements of this ambitious project. To assure highest instrument efficiency and best
image quality, each detector system needs to be tested to verify its usability, reliability and
stability.
The MUSE instrument CCDs are back-illuminated, deep depletion devices with a
graduated anti-reflection coating and manufactured by E2V. These science grade detectors
of type CCD231-84-4-D76 are customer specific grade chips that meet the ESO
requirements described in [1].