From instrumental design
to scientific exploitation


GYES [1] is a project for a high multiplex (≈ 500), high resolution (R ≈ 20 000), spectrograph to be placed at the prime focus of the CFHT. The main purpose of such an instrument is to conduct a spectroscopic survey complementary to the Gaia mission.

The final Gaia catalogue (expected around 2020) will provide accurate distances, proper motions and spectrophotometry for all the stars down to a magnitude of 20. The spectroscopic instrument on board the Gaia satellite (RVS) will provide intermediate resolution (R = 11 500) spectra for stars down to the 17th magnitude. For the fainter stars there will be no radial velocity information. For all the stars the chemical information will be limited to a few species. For the fainter stars the spectro-photometry will only provide a mean “metallicity”. The combination of parallaxes and proper motions will provide transverse velocities with an accuracy better than 1 km s−1 for the majority of stars within 1 kpc. However, this accuracy will not be matched by the radial velocities provided by the RVS for the stars fainter than about 13. A reliable analysis of the Galactic dynamics requires an accuracy of the order of 1 km s−1 for all the components of the velocity.

For all of the above reasons, wide field high resolution spectroscopic surveys from ground based facilities appear as a necessary complement to guarantee the maximum scientific throughput of the Gaia mission. The wide field of view attainable at the prime focus of 4m class telescopes makes these an attractive option for placing a multi-object spectrograph. This is in fact the choice already made by the Anglo Australian Telescope, with the HERMES project. The Canada-France-Hawaii Telescope has a long tradition in providing a stable prime focus environment for astronomical instrumentation and it thus appears a natural choice to study the feasibility of multi-object fibre-fed spectrograph for this telescope. The two projects would be strongly complementary since HERMES will have access to the southern hemisphere, while GYES to the northern hemisphere.

Leading team
Role Name
Principal Investigator Piercarlo Bonifacio
Project Scientist Patrick François
Elisabetta Caffau
Instrument Scientist Frédéric Royer
System Engineer Shan Mignot
Project Manager Jean-Laurent Dournaux

More details can be found at

[1] In Greek mythology, GYES is one of the three hecatonchires, giants having a hundred hands and fifty heads, children of Gaia (Earth) and Uranus (sky). It also stands as an acronym for Gaia surveY Extension Spectrograph.

GYES - conceptual design review

The current feasibility study of GYES culminated in a Conceptual Design Review (CoDR) in order to convince the CFH and the funding agencies that the GYES experiment can be successful. This includes developing the instrument, carrying out the...

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GYES - feasibility study

The midterm review of the GYES feasibility study took place during the SPIE meeting in San Diego, beginning of July 2010. It was successful.

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