The Utrecht Echelle Spectrograph (UES) is the principal high-resolution
spectrograph for the William Herschel Telescope. It offers the means to obtain
spectra of objects as faint as 
magnitude with a resolving power R
between 
and 
. The spectrograph has been designed to
operate from 3000 to 10000 Å; the wavelength interval covered in a single
exposure depends on the detector in use, and is typically in excess of 1000 Å.
UES is permanently located in a thermally stable enclosure on one of the Nasmyth
platforms at the f/11 focus of the WHT and can normally be deployed quickly from
one of the other focal stations. The optical design of the spectrograph is very
similar that of the University College London Echelle Spectrograph in use at the
coudé focus of the Anglo-Australian Telescope, described by Walker & Diego
1985 (MNRAS, 217, 355). A detailed description of UES and its operation is given
in the UES manual by S. Unger, M. Pettini and N. Walton (User Manual No.
XXIII).