Spectropolarimetry with a cube beamsplitter |
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| Authors: | Gordon Walker Nadine Dinshaw Leslie Saddlemyer Frank Younger |
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| Institution: | (1) Geophysics and Astronomy Department, University of British Columbia, V6T 1Z4 Vancouver, BC, Canada;(2) Dominion Astrophysical Observatory, 5071 West Saanich Road, RR 5, V8X 4M6 Victoria, BC, Canada;(3) Present address: Steward Observatory, University of Arizona, 85721 Tucson, AZ, U.S.A. |
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| Abstract: | For less than $2000 in materials we have exploited the DAO 1.8 m Cassegrain spectrograph between 430 and 800 nm for differential linear spectropolarimetry at resolutions up to  30,000 by using a beamsplitting cube as single-channel analyser. The position angle of the cube is under microprocessor control and, to counteract the highly erratic response of the spectrograph image-slicer combination to linear polarisation, we convert to circular polarisation by inserting a quarter-wave plate. The analyser has 40% throughput (c.f. 50% ideal) and we can sense polarisation levels as small as 0.01% with a CCD. Incomplete action of the quater-wave plate is probably the ultimate limit to precision. Details of the reduction procedure are given together with illustrative results for the Be star  Per. |
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