GYES

a wide-field multi-object spectrograph at the prime focus of CFHT

  • Multiplex - 500 objects
  • Large field of view - 0.9deg (diameter)
  • Spectral domains - blue and red
  • Resolution 20,000 (centre of domains)
  • Efficiency - 20% throughput - optimize telescope time
  • Simplicity - fixed wavelength settings - no mechanism in spectrograph - limited maintenance
  • Schedule - Gaia initial data release (2014-2015)

    The main requirements

  • 2 spectral domains with R=20,000
    - 390-450nm
    - 588- 670nm
  • Aim: S/N=100 at V=14 in 1 hour
    Up to 1 million stars will be observed
  • Accurate metallicities & abundances for numerous species (Li,Na,Mg,O,Al, Si, Ca, Ti,Mn,Sc,Co,Sr,Y,Ba,...) down to V=16
  • Accurate radial velocities down to V=18 for cool stars
    - sigma Vr < 1 km/s

    • Science goals

  • Thin disc - Thick disc
    - chemical dissection of the disc. Identification of sub-structures
    - measure of the level of homogeneity of the elements in various environments (arms / inter-arms, outer disc, bar, etc.)
    - thick disc :Interface with the thin disc at the metal-rich end and the halo on the metal-poor side
  • Bulge
    - detailed analysis of the bulge. Constraints on the bulge formation scenarii (hierarchical merging of sub-clumps, secular evolution of the disc through a bar forming a pseudo-bulge)
    - unprecedented combination of kinematics with abundance ratios ([alpha/Fe])
  • Halo
    - detailed abundance ratios of more than 10 000 halo stars. Chemical evolution of the early galaxy
    - search for Very Metal Poor stars with [Fe/H] < -4
  • Hot Stars and ISM
     - B/Be stars - A/Ap stars - mapping of the ISM
  • Pulsating Stars : Cepheids
    - P-L relation- galactic gradients
  • Open Clusters: 190 targets for GYES
     - age-metallicity relation - chemical history of the thin disk
    - chemical characterization of new OCs identified by Gaia
  • Globular Clusters: 49 targets for GYES
     - internal dynamics - multiple stellar populations identification

    • The GYES Survey

  • Target selection with Gaia's initial data release (with 2MASS cross_id)
    - thin/thick disc : several l and b directions with |b| < 30 - 300 fields
    - halo stars : within 60 degrees from the galactic center - 200 fields
    - bulge : window around l=1, b=-4 , high extinction => longer exposures - 70 fields
    - open clusters : observe stars between V=4.5 and V= 16 - 191 fields
    - globular Clusters : observe stars between V=4.5 and V=16 - 33 fields
  • Multiple exposure for binarity identification, pulsating stars
  • Simultaneous calibration with well know bright stars

    • 275 nights (including overhead) , 55 nights/year over 5 years

    The spectrograph

  • Technical description
    - fiber injection: input F/# = 3.65, output F/# = 3.5
    - slit size: 152 µm
    - collimator: F/# = 3.5, size = 240mm x 390mm
    - dichroic merged with the protective layer of the first VPH of the blue
    path - VPH: O 300 mm, blue: 2820 G/mm, red: 1880 G/mm
    - objectif: F/# = 1.2
  • Notable points
    - Two VPH gratings in chain to lower the components diameters and access to high resolution (nominal resolution of 20 000)
    - Optimised for transmission: spectral bandwidths + VPH efficiency
    - No moving part (simplified mechanical design and maintenance