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Ultraviolet spectropolarimetry of four interacting binaries was obtained with the Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) during the 16 day Astro-2 mission in March 1995. These included AO Cas, Vela X-1, V356 Sgr, and Beta Lyrae. Supporting visible-wavelength observations at Pine Bluff Observatory have been obtained for AO Cas, V356 Sgr, and Beta Lyr, giving a combined spectropolarimetric coverage from 1400 angstroms to 1.05 microns at a resolution R=200-600.
The observations of Beta Lyr, which represent the first spectropolarimetry of this classic active mass transfer object at any wavelength, are particularly intriguing. Taken together, the polarization spectrum resembles that of several of the Be stars observed by WUPPE, with strong visible wavelength polarization (0.5-0.75%), a large polarimetric Balmer jump, and a strongly suppressed UV polarization. The phase dependence of the polarization obtained from the visible wavelength data shows that the polarization Balmer jump is persistent but variable with phase, the polarization slope in the Balmer continuum is strongly variable with phase, and the position angle is relatively constant.
This work has been supported by NASA contract NAS5-26777 with the University of Wisconsin.
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