The High Optical Resolution Spectrograph (HORS) is a proposed high-resolution spectrograph for the
10-m Gran Telescopio Canarias (GTC) based on components from UES, a spectrograph which was in
use at the 4.2-m William Herschel Telescope (WHT) between 1992 and 2001.
HORS is designed as a cross-dispersed echelle spectrograph to observe in the range 380-800 nm with
a FWHM resolving power of about 50,000. HORS would operate on the GTC as a general-purpose
high-resolution spectrograph, and it would serve as a test-bed for some of the technologies proposed
for ESPRESSO – an ultra-high stability spectrograph planned for the Very Large Telescope (VLT) of
the European Southern Observatory.
The HORS spectrograph will be placed in the Coudé room, where it can enjoy excellent thermal and
mechanical stability, fiber fed from the Nasmyth focus, which is shared with OSIRIS. Inside the
spectrograph, incoming light will hit a small folder mirror before reaching the collimator. After a
second folder, the light will go through a set of three prisms and an Echelle grating before entering the
spectrograph camera and, finally, reaching the detector.
This manuscript contains a summary of the whole process that has transformed UES into HORS, with
all the mechanical and optical modifications that have been introduced to reach the final layout.