Taurus II is a more powerful and user-friendly version of the original Taurus imaging Fabry-Perot interferometer which was used at the AAT between 1981 and 1983. Details of the original Taurus are given by Atherton et al. (1982 MNRAS 201,661). The system is designed primarily for mapping velocity fields of emission-line objects, and it has many advantages over conventional grating spectrographs when studying the dynamics of extended objects. Taurus is most often used with the IPCS, but can also be used with a CCD in some applications, such as narrow-band direct imaging.
Taurus II is mounted at the f/8 Cassegrain focus and can access a 9' field at a resolving power of between 500 and 60,000. By scanning an etalon through a single interference order and sampling the resultant image over about 100 steps through the order, a three-dimensional data set (with two spatial and one spectral dimension) is created. This can be analysed to derive, for example, the velocity field of a large emission-line galaxy or gaseous nebula. Table 5.3 lists the etalons currently available (FSR is the free spectral range). Many of the etalons are shared with the northern hemisphere Taurus, and several months notice should be given if a particular etalon is needed for AAT observing.
Taurus also has a faint object polarimetry (FOP) mode in which the Taurus II focal reducer is operated at the f/15 Cassegrain focus with a quarter-wave plate and Wollaston prism in the collimated beam. The O-ray and E-ray images are separated by 20", in principle allowing slot masks to be used at the input focal plane for diffuse object work. The main mode of operation, however, is to image a stellar source through the system, thereby obtaining star and sky in the two polarization states, with the quarter-wave plate used for circular polarization observations.
Taurus II is a flexible and somewhat complex instrument. There is presently no instrument manual, and intending observers should direct any enquiries to the AAO instrument scientist at Epping, or by electronic mail to the AAO Director.
Table 5.3: Taurus II etalons
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