One of the telescopes at the University of Wisconsin's Pine Bluff Observatory (PBO) is a 0.9 m f/13.5 Cassegrain with a dedicated spectropolarimeter (HPOL). From February 1989 to December 1994 this instrument obtained simultaneous spectra and polarization measurements, with a resolution of 25Å, from 3200Å -7600Å for 311 targets. A halfwave plate rotated to 8 distinct angles provide the spectropolarimetric modulation. The detector was a Reticon dual-photocathode array with 1024 diodes in each array. (In 1995 the detector was replaced by a 400 x 1200 CCD with spectral coverage 3200Å -10500Å.) See Wolff, Nordsieck and Nook, 1996, A.J., 111, 856 [pdf] for a detailed description of the instrument. See also the HPOL Project Web site.
HPOL PBO Reticon Halfwave Data Set
These data have been processed by summing equivalent readouts on a particular object, subtraction of background scans, division by the flat field calibration spectra, flux calibration using spectra of known bright stars, and polarimetric calibration using data obtained of unpolarized and polarized standards. For the halfwave mode data, the modulated scans are differenced and a Fourier analysis, pixel-by-pixel as a function of waveplate angle, is done to give Stokes parameters %Q and %U spectra along with a %Error spectrum, all consisting of 1024 32-bit data points for each array from about 3200Å -7700Å with a 25Å resolution.
Data analysis and software development took place at the University of Wisconsin Space Astronomy Laboratory (SAL). Much of the data reduction was accomplished by a FORTRAN language package (REDUCE) generalized for a collection of Reticon detector/spectropolarimeters developed at SAL to support ground-based (HPOL/PBO), the space shuttle-flown Wisconsin Ultraviolet Photo Polarimeter Experiment (WUPPE) and Rocket UV spectropolarimetry. This software package was initially installed on UNIX based microVAXes for several years and is currently on SiliconGraphics machines running IRIX and machines running Linux.