CFHT, Instruments, Spectroscopy, Gecko: The Coudé f/4 Spectrograph

Web Manual for Gecko - Introduction

This Web Manual attempts to provide as much information as possible about the basic design and use of the CFHT f/4 Coudé high-resolution spectrograph, Gecko (Grating EChelle speKtrOgraph).

Unlike most echelle spectrographs, Gecko has been optimized for use with a single spectral order (between 5 and 18) from a 316 groove/mm echellette mosaic. Since spectra for these orders normally overlap, order sorting is achieved with interference filters or by one of three variable grisms. The average spectral resolving power (R) is of 120,000.

For observations between 3700Å and 10,000Å, the now decommissioned mirror train has been replaced by optical fibers running from the Cassegrain focus to the Coudé room. This CAssegrain Fiber Environment is called CAFE. A four-slice Bowen-Wallraven slicer is used to optimize the instrument throughput. Note that observations can actually be performed down to about 3500Å with CAFE, depending on the number of photons needed (see the throughput measurements table for numbers).

The entire spectrograph and CAFE unit are remotely controlled.

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