First ultraviolet spectropolarimetry of Be stars from the Wisconsin Ultraviolet Photo-Polarimeter Experiment

Abstract

We present the first ultraviolet (UV) spectropolarimetric observations of Be stars. They were obtained with the Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) aboard the Astro-1 mission. We present WUPPE data on the Be stars C Tau and % Aqr, along with near-simultaneous optical data obtained at the Pine Bluff Observatory (PBO). Combined WUPPE and PBO data give polarization as a function of wavelength across a very broad spectral region, from 1400 to 7600 Â. Existing Be star models predicted increasing polarization toward shorter wavelengths in the UV, but this is not supported by the WUPPE observations. Instead, the observations show a constant or slightly declining continuum polarization shortward of the Balmer jump, and broad UV polarization dips around 1700 and 1900 Â, which we suggest may be a result of Fe line attenuation effects on the polarized flux. Supporting evidence for this conclusion comes from the optical data, in which we have discovered decreases in polarization across Fe n lines in £ Tau.