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Session 57 - Astrophysical Diagnostics from Polarimetry.
Display session, Wednesday, June 12
Tripp Commons,
We report on four seasons (1987, 1988, 1989, 1992) of four-filter elliptical (linear+circular) polarimetry of the complex interacting binary star Beta Lyrae. These data were obtained at the Flower and Cook Observatory of the University of Pennsylvania. The B, V, and R bandpasses are very close to those of the Johnson system; the U bandpass is not quite so close, but it does straddle the Balmer jump. We have obtained 90 V-band measures, with excellent phase coverage, and 15 measures at the other wavelengths.
The V-band linear polarization data are clearly phase dependent, and the corresponding B- and R- band data are morphologically quite similar. The data between phases 0.5 and 1.1 vary smoothly, consistent with one or more stable, localized scattering regions. The data at other phases, however, exhibit noise with a semi-amplitude of \sim 0.1%. The phase behavior of the measures in the Stokes (Q,U) plane is complex, but there appears to be a simple linear relationship between the Stokes Q and U parameters consistent with an inclination close to 90^\circ. The circular polarization is not statistically significant. Our observations are consistent with those of earlier workers. The data analysis includes Fourier fitting at the 13-day orbital period and the nominal 282-day intrinsic cycle, as well as detailed modelling with the Wilson-Devinney light-curve computer code modified for polarimetry.
