| Abstract |
Linear spectropolarimetry of spectral lines is a neglected field in
astronomy, largely because of the lack of instrumentation. Techniques
that have been applied, but rarely, include investigation of the
dynamics of scattering envelopes through the polarization of electron-
or dust-scattered nebular light. Untried techniques include promising
new magnetic diagnostics like the Hanle Effect in the far-ultraviolet
and magnetic realignment in the visible. The University of Wisconsin
Space Astronomy Lab is developing instrumentation for such
investigations. In the visible, the Prime Focus Imaging Spectrograph
(PFIS) is a first light instrument for the Southern African Large
Telescope (SALT), which at an aperture of 11m will be the largest single
telescope in the Southern Hemisphere. Scheduled for commissioning in
late 2004, PFIS is a versatile high-throughput imaging spectrograph
using volume-phase holographic gratings for spectroscopic programs from
320nm to 900nm at resolutions of R=500 to R=6000. A dual-etalon
Fabry-Perot subsystem enables imaging spectroscopy at R=500 and R=3000
or 12,500. The polarization subsystem, consisting of a very large
calcite polarizing beam-splitter used in conjunction with half- and
quarter-wave Pancharatnam superachromatic plates, allow linear or
circular polarimetric measurements in any of the spectroscopic modes. In
the FUV, the Far-Ultraviolet SpectroPolarimeter (FUSP) is a sounding
rocket payload, scheduled for its first flight in 2003, that will obtain
the first high-precision spectropolarimetry from 105 - 150 nm, and the
first astronomical polarimetry of any kind below 130 nm. The 50 cm
primary mirror of the telescope is F/2.5. At the prime focus are the
polarimetric optics, a stressed lithium fluoride rotating waveplate,
followed by a synthetic diamond Brewster-angle mirror. The spectrometer
uses an aberration-corrected spherical holographic grating and a
UV-sensitized CCD detector, for a spectral resolution of R=1800. |