MOMFOS - Multi-Object Multi-Fiber Optical Spectrograph


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An Echidna-style fibre positioner for the GSMT


Spectroscopic analysis is when light from an object seen by a telescope is spread out into its component colours. This allows detailed measurements of the composition of the object, of gases between the object and us, even of how far away the object is. It's a very important part of astronomy.

Multi-object spectroscopy is when light from more than one object seen by a telescope at the same time is collected and independently analysed by spreading it into spectra. This can speed up the process of collecting the spectra of many objects, simply because it does more than one object at a time.

Fibre-fed multi-object spectroscopy is when the light for multi-object spectroscopy is collected in optical fibres. A telescope looks at the sky and forms an image of a field of stars. A fibre is placed precisely onto the image of a star and acts as a 'light pipe', carrying the light to a spectrograph for analysis.

The AAO's 'Echidna' concept positions hundreds of fibres for this purpose, each mounted in a movable 'spine'. The whole arrangement of hundreds of movable spines looks rather like the spines of an echidna. The spines are moved to put the ends of the fibres on the star images in the telescope's focal plane.

The Echidna concept is powerful because a lot of fibres can be accurately positioned in a small image. Some very big telescopes naturally form quite small images, and so an Echidna system is the best way to enable multi-object spectroscopy on these telescopes, to analyse hundreds of objects at the same time.

MOMFOS - the Multi-Object Multi-Fiber Optical Spectrograph - is a proposed instrument for the Giant Segmented Mirror Telescope (GSMT). This 30-metre telescope doesn't yet exist but its design is being coordinated by the Association of Universities for Research in Astronomy (AURA) New Initiatives Office, with the aim of beginning construction by 2010. It will have nearly ten times the light collecting power of the biggest telescopes built till now.

The AAO is performing a design study to investigate the feasibility of building an Echidna-style fibre positioner for MOMFOS.

To work in this application, the spines will need to be packed more tightly together than in the existing Echidna design, and a new system for measuring the positions of the spine tips must be developed.

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Originally created by Andrew McGrath on January 24, 2003