High Optical Resolution Spectrograph

sky spectrum obtained with HORuS
Responsible scientist
Allende Prieto
Operation year

    HORuS is a high-resolution (R=25000) spectrograph for the 10m Gran Telescopio Canarias (GTC). It collects light at the Nasmyth focal plane, shared with OSIRIS, using a 3x3 IFU (2.1x2.1 arcsec) with microlenses, into optical fibers that form a pseudo-slit at the spectrograph entrance. The light is dispersed with a 79 gr/mm echelle grating and cross-dispersed with three prisms, providing almost continuous coverage between 380 and 690 nm.

    In a 30-min integration HORuS gets a S/N ~ 1500, 250, 35 at 500 nm per resolution element for a V=7, 11, 15 mag solar-like star, respectively.  The grating and cross-dispersion prisms are fixed, and therefore so is the spectral coverage. 

    Resolving power: 25,000

    Spectral coverage: 380-690 nm

    The Utrecht Echelle Spectrograph (UES) was a high-resolution spectrograph in use at the William Herschel Telescope (WHT) in the Observatorio del Roque de los Muchachos between 1992 and 2001. It was a cross-dispersed echelle spectrograph designed to observe in the range 300-1100 nm with a FWHM resolving power between 40,000 and 80,000 (Unger et al. 1993). UES had been in storage since its removal from the Nasmyth focus of the WHT.  As there was no high-dispersion spectrograph available or planned for GTC, Ramón J. García López proposed that UES could be adapted for this telescope, and in 2007 the Isaac Newton Group handed the instrument over to the IAC.

    We have build HORuS using the components from UES, changing slightly its design to make it more compact, and fiber feeding it from one of the GTC Nasmyth foci.

    The commissioning of HORuS ended in March 2019, and it was first offered to GTC users in the second semester of 2019. Since the instrument's acquisition arm is placed inside OSIRIS, operations will be interrupted when OSIRIS is moved to the Cassegrain focus, sometime in 2020, and will hopefully be continued after the acquisition arm is anchored to the optical bench of the adaptive optics.

    Related Projects

    • Optical bench
      HORuS - High Optical Resolution Spectrograph
      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.
      Allende Prieto

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