First light: April 1985.
De-commissioned: February 1989.
Description: TAURUS is a wide-field, imaging Fabry-Perot
interferometer designed to obtain seeing-limited spectral information of
extended emission-line objects (in the wavelength range 4300-7100 Å).
It produces monochromatic pictures of nebulae, which can then be interpreted
to understand their motions and their three-dimensional structure. The
telescope beam is collimated, passed through a piezo-scanned Fabry-Perot
etalon and re-imaged onto the Image Photon Counting System. Depending on
the choice of the etalon, resolutions between 0.07 and 12 Å are available.
The etalon is the active component in TAURUS; it is the means by which
the lights is dispersed (or, to be more accurate, interfered) into its
component colours. It consists of two highly polished and reflective quartz
plates, kept parallel by means of a technique known as capacitance micrrometry.
The surfaces are flat to 0.002 µm and have to be kept actively parallel
to this same accuracy over their entire 60 mm diameter surface.
Each quartz plate weighs about 0.5 Kg
and has to be kept parallel to this tolerance at all orientations of the
telescope. The capacitance micrometry is a technique for determining relative
distances extremely accurately and, within a feedback loop, allow one to
drive a set of piezo stacks so that parallelism is locked by means of an
accurate servo. the separation of the plates has then to be changed through
a distance of 0.25 µm - while, of course, maintaining their parallelism.
Applications of TAURUS include (in order
of decreasing resolution): velocity fields in planetary nebulae, HII regions,
supernova remnants, spiral, irregular and interacting galaxies, narrow-band
photometry of distant galaxies and galaxy clusters, and quasar