Fibre Multi Object Spectrograph

Fibre Multi Object Spectrograph, or FMOS is facility instrument for the Subaru telescope on Mauna Kea in Hawaii. The instrument consists of a complex fibre-optic positioning system mounted at the prime focus of the telescope. Fibres are then fed to a pair of large spectrographs, each weighing nearly 3000kg. The instrument will be used to look at the light from up to 400 stars or galaxies simultaneously over a field of view of 30 arcminutes (about the size of the full moon on the sky. The instrument will be used for a number of key programmes, including Galaxy Formation and Evolution and Dark Energy via a measurement of the rate at which the universe is expanding.

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It is currently being built by a consortium of institutes led by Kyoto University and Oxford University with parts also being manufactured by the Rutherford Appleton Laboratory, Durham University and the Anglo-Australian Observatory. The instrument is scheduled for engineering first-light in early 2008.

The Spectrograph The spectrographs use a technique called OH-suppression to increase the sensitivity of the observations: The incoming light from the fibres is dispersed to a relatively high resolution and this spectrum forms an image on a pair of spherical mirrors which have been etched at the positions corresponding to the bright OH-lines. This spectrum is then re-imaged through a second [[Diffraction Grating] to allow the full spectrum (without the OH lines) to be imaged onto a single infrared detector.

References

• FMOS
• FMOS Project