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The FOSs are fixed-format low-dispersion spectrographs of special design matched to the optical characteristics of the telescope in order to optimize throughput. The spectrum covers the whole wavelength range from 3500Å up to 10500Å . There are two spectral orders, both slightly curved, which requires precise treatment during data reduction. A set of special atmospheric standards is usually required to (flux) calibrate the red part of the spectrum. Data reduction is best done by using the Durham FOS software package, but reduction can be done using standard IRAF functions.
This spectrograph comes with a set of 15 different gratings, which cater for low dispersion spectroscopy at 16Å resolution all the way up to `high' dispersion spectroscopy at 0.3Å resolution, and corresponding spectral coverage. There are two cameras, on a short focus and a long focus arm, each with its own detector mounted (CCD or, previous to 1992, IPCS); it is possible to switch from one arm to the other during an observing night, but both arms cannot be used simultaneously. Data reduction for CCD observations is standard; long-slit observations taken with the IPCS may require an advanced two-dimensional package (see section ). On rare occasions the IDS has been used in a cross-dispersed mode.
This is an intermediate dispersion spectrograph with two independent cameras, one on the blue and one on the red arm. Both cameras can be used simultaneously, thus one may find in the archive sets of two ISIS observations taken at the same time. The blue arm can be equiped with either a blue-sensitive CCD or the IPCS, the red arm always carries a CCD detector. Sometimes only one camera is used. A range of gratings is available to allow spectroscopy from low to high resolution. ISIS can also be used in spectropolarimetrical mode, for which purpose active optical elements can be inserted into the lightpath. The polarization information is available in the archive catalogue.
A very stable high-dispersion echelle spectrograph resident on the Nasmyth platform of the WHT. UES requires a large detector (10001000 CCD) in order to have a large spectral coverage. UES has also been used with the WHT IPCS detector on very faint objects. UES data can be reduced routinely with the IRAF or FIGARO/ERIS software packages.
A very stable, off-axis spectrograph at the JKT Cassegrain focus, for low and intermediate dispersion (resolution 1Å to 10Å ) spectroscopy. The grating setting on this instrument is not under computer control, and done manually.