Instrument's Characteristics

A short instrument description and an overview of the observational capabilities and expected performance of UVES are provided below. A comprehensive description of the instrument is given in the User Manual. UVES is a two-arm cross-dispersed echelle spectrograph covering the wavelength range 300 - 500 nm (Blue) and 420 - 1100 nm (Red), with the possibility to use dichroic beam splitters. The spectral resolution for a 1-arcsec slit is about 40,000. The maximum resolution that can be reached with still adequate sampling, using a narrow slit, is about 80,000 in the Blue and 110,000 in the Red. The dioptric cameras offer fields with a diameter of 43.5 mm (Blue) and 87 mm (Red) and have external focal planes for easy detector interfacing and upgrading during the lifetime of the instrument.The two arms of UVES are equipped with CCD detectors, one single chip in the Blue arm and a mosaic of two chips in the Red arm. The Blue CCD is a 2K x 4K,15 µm pixel size thinned EEV CCD-44. The Red CCD mosaic is made of an EEV chip of the same type (EEV CCD-44) and the MIT/LL CCID-20 chip, which features a higher NIR QE and reduced fringing, for the redder part of the spectral range. Each arm has two cross-disperser gratings working in first spectral order; the typical order separation is 10 arcsec.

Auxiliary devices include the usual calibration lamps, an Iodine absorption cell for high-precision radial velocity studies, three image slicers, a depolarizer, a field derotator, an Atmospheric Dispersion Compensator and filter wheels. A set of eight interference filters can be used for long-slit spectroscopy of spatially-extended targets. On-line information on the object position and the energy passed by the slits is provided by CCD slit viewers and exposure meters, respectively. UVES is equipped with a fibre port for eight fibers (e.g. six for objects, two for sky measurements) feeding the Red arm. With fibers of 1-arcsec diameter, this facility provides multi-object cross-dispersed echelle spectroscopy with R=47,000 in the spectral range 420 - 1100 nm. The fiber inputs are located in the focal plane of the Nasmyth station A of UT2 (Kueyen telescope) as part of the FLAMES facility. The UVES instrument components are placed inside a passive enclosure which provides thermal isolation from the outside environment. The control and CCD electronics are located in temperature-controlled cabinets outside the enclosure. All functions (image slicers, filters, ADC, etc.) are permanently on-board and remotely selectable without manual intervention. A continuous flow of liquid Nitrogen coolant for the CCDs is supplied by an external vessel with an autonomy of at least two weeks. These measures lead to high stability and repeatibility of calibrations both over short and extended periods of time.

The table below gives the measured observational capabilities and performance of the instrument.

Wavelength range
300 - 500 nm
420 - 1100 nm
Resolution-slit product
Max. resolving power
~80,000 (0.4" slit)
~110,000 (0.3" slit)
Limiting magnitude
(1.5 hr integration, S/N=10, seeing 0.7")
18.0 at R=58,000 in U (0.7" slit)
19.5 at R=62,000 in V (0.7" slit)
Overall detective quantum efficiency (DQE)
(from the top of the telescope, wide slit)
12% at 400 nm
14% at 600 nm
dioptric F/1.8, 70 µm/arcsec
field 43.5 mm diam.
dioptric F/2.5, 97 µm/arcsec
field 87 mm diam. 
(pixel scale)
EEV, 2Kx4K, 15 µm pixels
(0.22 arcsec/pix)
mosaic of two (EEV + MIT/LL), 2Kx4K, 15 µm pixels
(0.16 arcsec/pix)
41.59 g/mm, R4 mosaic
31.6 g/mm, R4 mosaic
g/mm and wavelength of max. efficiency
#1: 1000 g/mm, 360 nm
#2: 660 g/mm, 460 nm
#3: 600 g/mm, 560 nm
#4: 312 g/mm, 770 nm
Typical wavelength range/frame
[CD#1(#2) and CD#3(#4)]
85 (126) nm in 33 (31) orders
200 (403) nm in 37 (33) orders
Min. order separation
10 arcsec or 40 pixels
12 arcsec or 70 pixels

The UVES Exposure-Time Calculator allows to compute the detailed spectral formats on the individual CCDs for all instrument configurations. Further, the expected S/N for various input-flux distributions and environmental conditions can be computed together with additional configuration-dependent informations. The UVES ETC is based on the performances of UVES measured during the commissioning and subsequent periods of operations.

UVES links