XSHOOTER in a nutshell:
Publications based on data obtained with XSHOOTER should quote
the following reference paper:
Vernet et al. 2011, A&A, 536A, 105
The XSHOOTER science case document is available here.
XSHOOTER is a multi wavelength (300-2500nm) medium resolution
spectrograph mounted at the UT2 Cassegrain focus until end of P91. Starting from P92, XSHOOTER will be moved to UT3. Its location for P93 and above is not yet decided.
XSHOOTER consists of 4 arms with the Acquisition and Guiding camera.
It has 3 spectroscopic arms, each with
optimized optics, dispersive elements and detectors:
Each arm is an independent cross dispersed echelle spectrograph
completed with its own shutter and/or slit mask. The incoming light is
split into the three different spectrographs/arms through 2 dichroics
(cut off wavelengths 559.5 nm and 1024 nm for the
separation of the UVB-VIS light and VIS-NIR light, respectively). For each arm the spectral format is fixed. The orders in each detector are
highly curved and the sky/arc lines within each order are highly
Three piezo controlled mirrors, located in front of each
arm, guarantee that the optical path is maintained aligned against
instrument flexure and correct for differential atmospheric refraction
between the telescope guiding wavelength and each arm central
Two pairs of ADC (Atmospheric Dispersion Corrector) prisms in the
optical path of the UVB and VIS arm compensate for the atmospheric
dispersion at different airmasses. No ADC is mounted in front of the
NIR arm. Due to mechanical problems they were disabled.
The Acquisition and Guiding system (A&G) consists of a
1.5'x1.5' FoV technical CCD for the target acquisition and the imaging mode of XSHOOTER that will be offerred starting from P93. A filter
wheel equipped with the Johnson and SDSS filters can be used for the
acquisitions. There is not secondary guiding in XSHOOTER.
The five positions slide, located before the UVB, VIS and NIR
spectrograph, allows to insert an image slicer in the optical path and
perform IFU spectroscopy of a 1.8''x4'' FoV. IFU mode observations are an
alternative to slit mode observations.
An internal calibration unit, equipped with pen-ray (Ar, He, Ne
and Xe), Th-Ar, Halogen and D2 lamps, is used to produce the necessary
calibration frames (flats, arcs, oder definition, format check and 2D
- UVB, covering the wavelength range 300-559.5 nm
- VIS, covering the wavelength range 559.5-1024 nm
- NIR, covering the wavelength range 1024-2480 nm
The figure below shows the schematic overview of the instrument.