Spectropolarimetric Evidence for a Bipolar Flow in Beta LyraeJennifer L. Hoffman, Kenneth H. Nordsieck, and Geoffrey K. Fox |
| We present ultraviolet and visible spectropolarimetry of the interacting binary star Beta Lyrae, obtained with the Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) and the HPOL spectropolarimeter at Pine Bluff Observatory (PBO). Our observations span three years and cover the wavelength range from 1400 to 10500 A, with a resolution of 7.5 to 15 A. Detailed broad- and narrow-band spectropolarimetric analysis allows us to begin to decompose the complex spectrum of Beta Lyrae: by examining the polarization behavior of a line or continuum, we can determine which component scatters the light, and, ultimately, from which component that light originates. After removing interstellar polarization from our data and rotating the results to the apparent intrinsic position angle of the system, we find that the polarization of the hydrogen Balmer and vacuum-ultraviolet "UV bump" emission lines, as well as that of the near-ultraviolet continuum, remains mostly constant with phase and is oriented at 90 degrees to the visible polarization, indicating that the scattering plane of the light in these three spectral components is perpendicular to the scattering plane of the visible light. We propose that the UV-bump, Balmer- emission, and near-UV continuum polarization is produced by electron scattering off a bipolar outflow in the Beta Lyrae system. The intrinsic visible polarization of Beta Lyrae shows eclipses which associate it with material near the accretion disk. We find conflicting evidence regarding both the origin of this visible light the scattering surface which polarizes it: continuum evidence points toward the secondary object as the illuminator and the accretion disk edge as the scatterer, while line analysis suggests light from the loser scatters off material between it and the disk. The presence of material away from the orbital plane may help resolve this contradiction. |
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For reprints or more information, please send email to Jennifer. September 22, 2002 |