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ABSTRACT. A new, inexpensive polarimetric unit has been constructed for the Dominion Astrophysical Observatory (DAO) 1.8 m Plaskett telescope. It is implemented as a plug-in module for the telescope's existing Cassegrain spectrograph, and it enables medium-resolution (R ≈ 10; 000) circular spectropolarimetry of point sources. A dual-beam design, together with fast switching of the wave plate at rates up to 100 Hz and synchronized with charge shuffling on the CCD, is used to significantly reduce instrumental effects and achieve high-precision spectropolarimetric measurements for a very low cost. The instrument is optimized to work in the wavelength range of 4700-5300 Å to simultaneously detect polarization signals in the Hβ line, as well as nearby metallic lines. In this article we describe the technical details of the instrument, our observing strategy, and data reduction techniques, and we present tests of its scientific performance.

The near-infrared instruments on the James Webb Space Telescope will use 5 micron cutoff HAWAII-2RG detector arrays. We have investigated the response of this type of detector at sub-pixel resolution to determine whether variations at this scale would affect the performance of the instruments. Using a simple experimental setup we were able to get measurements with a resolution of approximately 4 microns. We have measured an un-hybridized HAWAII-1RG multiplexer, a hybridized HAWAII-1RG device with a 5 micron cutoff HgCdTe detector layer, and a hybridized HAWAII-2RG device with a 5 micron cutoff substrate-removed HgCdTe detector layer. We found that the intra-pixel response functions of the hybrid devices are basically smooth and well behaved, and vary little from pixel to pixel. However, we did find numerous sub-pixel sized defects, notably some long straight thin features like scratches. We were not able to detect any significant variations with wavelength between 0.65 and 2.2 microns, but in the -1RG device there was a variation with temperature. When cooled from 80K to 40K, the pixel response became narrower, and some signal began to be lost at the edges of the pixel. We believe this reflects a reduction in charge diffusion at the lower temperature.

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