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