First light: 15 August 1987.
De-commissioned: June 1999.
Designed and built by: Kapteyn Sterrenwacht Werkgroep in Roden, the
Netherlands, with some technical input from the RGO.
Description: TAURUS is a wide-field (9 arc min)
imaging Fabry-Perot interferometer originally developed jointly by the
RGO and Imperial College, London to map velocity fields of extended or
multiple astronomical emission-line sources. The original instrument was
in use at the INT, and TAURUS-2 is the new, fully automated version. It is
one of the Cassegrain instruments and its main use is in measuring velocity
fields of extended emission line objects - HII regions, planetary nebulae, supernova remnants and
galaxies.
It is designed to accommodate a number of dedicated aperture masks and
four etalons. Each etalon can be independently tuned to a defined frequency
passband. Two TAURUS-2 units were produced, one for the AAT and one for the
WHT. The WHT version was first used on 22 August 1987 for the first
PATT-allocated observing session on the new telescope.
TAURUS-2 has a capability greater than that of earlier versions. In
particular, the wavelength coverage has been extended to the range from 3650
Å to beyond 1 micron. In spite of the difference in focal ratio, the
collimators for the WHT are compact three-element telephoto systems of
similar design. The f/2 camera of focal length 120 mm consists of two
cemented triplet components and two doublets. The design minimizes the
number of air-glass surfaces. The wavelength range has been extended by
making the inner components of the triplets of calcium fluoride crystal.
There is no perceptible loss of efficiency in the presence of the external
stop at the etalon.
The optimum choice of focal length for the camera depends on the angular
size and surface brightness of the astronomical object. As an alternative
option to the f/2 camera normally used, an f/4 camera was built so as to
provide a larger image scale on smaller fields.
Although TAURUS-2 was originally constructed primarily for use as a
Fabry-Perot interferometer, it can also be used as a focal reducer for
imaging observations. The advantage of using TAURUS for imaging observations
over using a CCD direct (e.g. at the auxiliary port of the A&G)
is that it provides a plate scale better matched to the image size. When an
EEV CCD with a pixel size of 22 microns is used
direct at f/11, the scale is 0.1 arcsec/pixel, oversampling the image and
providing only a limited field. TAURUS with the f/4
camera provides a scale of 0.27 arcsec/pixel, whilst TAURUS with the f/2.1
camera provides a scale of 0.51 arcsec/pixel.
Some scientific highlights:
More information: TAURUS
Users' Manual
More photos of this instrument: http://www.ing.iac.es/PR/archive/wht/instruments.html