Overview

UVES is a cross-dispersed echelle spectrograph designed to operate withhigh efficiency from the atmospheric cut-off at 300 nm to the long wavelength limit of the CCD detectors (about 1100 nm). To this aim, the light beamfrom the telescope is split in two arms (UV to Blue, and Visual to Red) within the instrument. The two arms can be operated separately, or inparallel via a dichroic beam splitter. The resolving power is about 40,000when a 1-arcsec slit is used. The maximum (two-pixel) resolution is 80,000or 110,000 in the Blue- and the Red Arm, respectively. Three image slicers are also available to obtain high resolving power without excessive slit loss.The instrument is built for maximum mechanical stability and allows for accurate wavelength calibration. An iodine cell can be inserted in the light beam for observations requiring extremely high accuracy for radial velocity measurements.

The table below indicates, for a given mode, the accessible wavelength range, the maximum resolving power that can be obtained, the approximate wavelength range covered in one exposure, and an estimate of the limiting magnitude. Please note that for each instrument mode standard settings have been defined (see the User Manual). In service mode, only UVES standard settings are allowed.

Spectroscopic Modes
Instrument mode
Accessible λ range (nm)
Maximum resolution (λ/Δλ)
Covered λ range (nm)
Magnitude limits
Blue arm
300-500
80,000
80
17-18
Red arm
420-1100
110,000
200-400
18-19
Dichroic #1
300-400
80,000
80
17-18
 
500-1100
110,000
200
18-19
Dichroic #2
300-500
80,000
80
17-18
 
600-1100
110,000
400
18-19
Iodine cell
500-600
110,000
200
17

The magnitude limits listed above are estimated on the basis of the following conditions: continuum source, 0.7 arcsec seeing, 1 arcsecslit, no binning, 3-hour integration time, S/N of 10 (per resolutionelement) at the peak of the central order, no moon. They are indicative of the limiting performance of the instrument only as they depend on the wavelength. UVES proposers should use the ETC for their S/N estimates.

Whether or not an image slicer should be used depends on the trade off between slit losses due to seeing and the reduced transmission (reduction between 20 and 40%) when using an image slicer. The peculiar spectral formats and the reduced sample of the sky spectrum with the image slicer also have to be taken into account. Starting with P77, eight interference filters are offered for the use with the UVES Red arm in visitor mode. The purpose of these filters is to isolate certain echelle orders to allow the use of the maximum slit length of 30 arcsec. The central wavelengths of the filters are chosen to permit observations of the most important emission lines in extended objects. The filters and their central wavelengths are: Hα (656.6 nm), Hβ (486.1 nm), OIII (500.7 nm), OIII (436.3 nm), NII (575.5 nm), OI (630.0 nm), SII (672.4 nm) and HeII (468.6 nm). The peak transmissions of the filters range from 70-90%.