TAURUS is a wide-field imaging Fabry-Perot interferometer designed to obtain spectra over a field of up to 9 arcmin with a resolving power anywhere between 2,000 and 100,000. Its main use is in measuring velocity fields of extended emission line objects --- HII regions, planetary nebulae, supernova remnants and galaxies.
The principles behind the operation of TAURUS are described in detail by Taylor & Atherton (Monthly Notices of the Royal Astronomical Society, vol 191, p675, 1980), Atherton et al. (Monthly Notices of the Royal Astronomical Society, vol 201, p661, 1982) and Taylor et al. (Indirect imaging, ed. J Roberts, publ. CUP, p379, 1984). These papers also give a description of the original version of TAURUS, which is no longer available. TAURUS-2, the instrument currently in use on the WHT, is described in Unger et al. (Monthly Notices of the Royal Astronomical Society, vol 242, p33p, 1990).
The way TAURUS operates is that the beam from the telescope is first collimated and then passed through a Fabry-Perot etalon. The field modulated by the Fabry-Perot interference rings is re-imaged by a camera onto a two-dimensional detector. The observing wavelength, and hence the order of interference at which the interferometer works, is determined by an order sorting filter, which can be placed either in the focal plane of the telescope, or in the collimated beam.
A TAURUS spectral scan normally consists of a large number (typically 60) of separate 2-dimensional images taken sequentially at different gap settings of the Fabry-Perot etalon, each giving a two-dimensional image in a different wavelength bin. By stacking these together it is possible to build up a 3-dimensional spectral line datacube.