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Ian Skillen
ISIS Instrument Specialist


ISIS on the Cassegrain focus of the WHT

The Intermediate dispersion Spectrograph and Imaging System (ISIS) is mounted at the Cassegrain focus of the 4.2m William Herschel Telescope. ISIS is a high-efficiency, double-armed, medium-resolution (8-120 Å/mm) spectrograph, capable of long-slit work up to ~4' slit length and ~22" slit width. Use of dichroic slides permits simultaneous observing in both blue and red arms, which are optimised for their respective wavelength ranges. Linear and circular spectropolarimetry and imaging polarimetry are also available.

The CCD currently in use on the blue arm of ISIS is a thinned, blue-sensitive EEV12, an array of 4096×2048 (13.5 micron) pixels. This is the default device for the ISIS blue arm. The default chip for the ISIS red arm is RED+. It is a red-sensitive array of 4096×2048 (15.0 micron) pixels with almost no fringing.

For fast or faint-object spectroscopy, two EMCCDs (QUCAM2 and QUCAM3) are available for both arms of ISIS. They provide high-speed spectroscopic capability (to about 10Hz) with very little dead time and essentially zero read noise. EMCCDs have distinctive features and optimising their use depends critically on the scientific goals.

In February 2012 ISIS 4MS controllers were replaced by new PLC (Programmable logic controller) system that is more reliable, increases a speed of all mechanism movements and offers continued maintenance and better transparency in identifying problems.

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Contact:  (ISIS Instrument Specialist)
Last modified: 13 November 2013