The High Optical Resolution Ultra-stable Spectrograph (HORUS) 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. HORUS 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. HORUS 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 – a ultra-high stability spectrograph planned for the Very Large Telescope  (VLT) of the European Southern Observatory.  

The new instrument would enjoy an extreme stability by being fiber-fed and placed at the Coudé room,  in addition to mechanically, and pressure isolated. Sharing focus with OSIRIS would provide an opportunity to enhance the productivity of GTC. 

HORUS on GTC would enable the study of chemical compositions of celestial objects (stars, stellar clusters,  comets, nebulae, …), opening up to GTC many research fields such as stellar nucleosynthesis, stellar structure  and evolution,  galactic chemical evolution or galaxy assembly. By ensuring extreme wavelength stability, HORUS on GTC would also have the ability to characterize stars hosting planets, and to  discover and follow-up planetary systems from radial velocity variations.