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Home > Public Information > Manchester Echelle Spectrograph

William Herschel Telescope and Isaac Newton Telescope

MES: Manchester Echelle Spectrograph

First light: November 1987.

Designed and built by: Manchester University.

Description: The optical configuration consists of a lens, designed by Charles Wynne, which both collimates the incoming beam from the telescope and refocusses the spectrum after the nearly Littrow dispersion by the echelle grating. No cross-dispersion is employed. The separate echelle orders, each containing one or more nebular emission lines, are isolated with highly efficient, three period interference filters. IPCS is the favoured detector, though CCDs can be used with effect in certain applications.

This simple optical layout, transmission optics with three layer anti-reflection coatings throughout and the quasi-Littrow configuration of a reflection echelle grating, all combine to achieve an exceptionally high luminosity-resolution product for the spectrometer. One penalty for this optimization is the restriction to 3900-7500 Å of the operating wavelength range.

The luminosity-resolution product is enhanced further for particular astrophysical problems by having a variety of options for the entrance slits. Either a single long slit or a multi-slit with up to five long slits transmitting simultaneously are routinely employed. Separate file profiles are obtained for each resolvable element along these slits. Where emission and absorption line sources are distributed randomly within the entrance aperture, multi-image masks, pre-arranged to accept the light from the separate sources, can be used.

Six separate fibre arrays are assembled for use in the fibre mode (MATADOR). Here the entrance of the fibres (with up to 529 being employed in one array) are arranged to match the shapes of various sources in the focal plane of the telescope. The output ends of the fibres are then distributed along up to five entrance slits of the spectrometer.

In their primary mode the Manchester echelle spectrometers fill a distinct niche between more traditional, cross-dispersed, echelle spectrometers, which are primarily useful for small sources over very large wavelength ranges, and the stepped Fabry-Perot devices such as TAURUS which are most usefully applied to very extensive sources but over very small wavelength ranges. The fibre-optic format changers extend the Manchester echelle´s application to some extent into TAURUS territory.

The primary use of these dedicated echelle spectrometers is for problems which require emission or absorption line profiles, at high signal to noise ratios and reasonably high spectral resolutions, from many separate spatial elements of a source simultaneously.

The imaging mode of the Manchester echelle spectrometers, which was originally introduced as a minor alternative, has proved extraordinarily useful in practice. Here the slit assembly is replaced by a clear aperture and the plane mirror is inserted.

Publications (scientific papers, technical publications, etc.).

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Last modified: 22 August 2016