Tmt night

Wide-Field Optical Spectrometer (WFOS)

Field of View
40.5 arcmin2 (need not be continuous)

Wavelength Range
0.31 – 1.0 µm

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

Spatial Sampling
0.15 arcsec per pixel, goal < 0.1 arcsec

Spectral Resolution
R = 500-5000 for a 0.75 arcsec slit, 150-7500 (goal)

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

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

Status: Conceptual Design


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


Pricipal Investigator
Kevin Bundy (UCSC)
Wide-field Optical Spectrometer

The Wide Field Optical Spectrometer (WFOS) will provide near-ultraviolet and optical (0.3 – 1.0 μm wavelength) imaging and spectroscopy over a more than 40 square arcminute field-of-view. Using precision cut focal plane masks, WFOS will enable long-slit observations of single objects as well as short-slit observations of hundreds of objects simultaneously. WFOS will use natural (uncorrected) seeing images.

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. The basic design of the support structure and enclosure will also offer ready access to all configurable portions of the instrument, such as the ADC, slit masks, dichroics, filters, gratings, and detectors to facilitate set-up and maintenance. WFOS is being designed so as not to preclude additional functionality such as an integral field unit, a tunable filter for narrow-band imaging, and an interface to a possible future Ground-Layer Adaptive Optics system for improving the images delivered to the instrument, and thus allowing for higher-sensitivity observations.

WFOS has three modes of operation: direct imaging, single-object spectroscopy and multi-object spectroscopy. To achieve the maximum observing efficiency and maintain the TMT aperture advantage over current telescopes, it must be possible to switch between modes with minimal overhead, < 30 seconds for changing the disperser to a mirror (for imaging), or to change reflection grating and (if in ECH mode) cross-dispersing prism.

wfos schematic