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Wide-Field Optical Spectrometer (WFOS)


Status (October 2018): Architecture downselect complete. Conceptual Design Phase including refreshment of Science Requirements

Science with WFOS
  • Tomography of the high-redshift intergalactic medium
  • Gamma-ray bursts, supernovae, tidal flares and other transients
  • Rest-frame UV properties of high-redshift galaxies
Documents & Tools

WFOS project webpage


Principal Investigator
Kevin Bundy (UCSC)

Original Design Requirements (Subject to change)

Field of View
25.5 (8.3x3) arcmin2

Wavelength Range
0.31 – 1.0 µm (0.7 µm contiguous spectral range @R=1500)

Spatial Resolution 
Seeing limited (GLAO ready)

Image quality: imaging
0.2 arcsec FWHM over any 0.1µm wavelength interval (including contributions from the telescope and the ADC at z = 60°

Image quality: spectroscopy 0.2 arcsec FWHM at every wavelength

Total Slit Length
500 arcseconds (~62 targets with 8” slits)

Spatial Sampling
0.05 arcsec per pixel

Spectral Resolution
R = 1500-5000 @0.75" slits 15,000 @0.25" slits

30% from 0.31 – 1.0µm, or at least as good as that of the best existing spectrometers

texp=5x900s, S/N=150 per element, R=3500 V=20.5

Spectra should be photon noise limited for all exposure times > 60 sec. Background subtraction systematics must be negligible compared to photon noise for total exposure times as long as 100 Ksec. Nod and shuffle capability in the detectors may be desirable

Wavelength Stability
Flexure at a level of less than 0.15 arcsec at the detector is required

Xchange-WFOS: Slit mask based imaging spectrometer

The Xchange-WFOS will provide near-ultraviolet and optical (0.31 – 1.0 μm) imaging and spectroscopy over a 25 square arcminute field-of-view. Using precision cut focal plane masks, WFOS will enable short-slit observations of ~50 to 60 objects simultaneously. Xchange-WFOS will be able to be used in natural seeing or with GLAO correction. Between 1 and 4 seperate observations using articulating cameras will be needed to cover the full wavelength range, depending on the desired resolution.

Xchange-WFOS will incorporate a robust structure to support the various components of the instrument and minimize instrument flexure. In addition, it will incorporate an enclosure to protect its components and provide a light tight environment for the optical elements. Possible upgrades and additional functionality include an integral field unit, increased field of view and options for gratings if funding allows.

Xchange-WFOS Field of View

A potential Xchange-WFOS Field of View. Alternative collimator designs need to be evaluated, the FOV in some designs is 'on-axis'.

Xchange-WFOS instrument concept and camera optical concept

Xchange-WFOS instrument concept and camera optical concept