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. Use of dichroic slides permits
simultaneous observing in both the blue and red arms,
which are optimised for their respective wavelength ranges.
Linear and circular spectropolarimetry and imaging polarimetry are also available, as well as
a drift-scan mode for high-time resolution monitoring programmes.
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 ISIS red 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.
