Locating mass loss: Numerical modeling of circumstellar material in binary systems

I have used spectropolarimetric observations combined with three-dimensional Monte Carlo radiative transfer models to investigate the geometrical and optical characteristics of circumstellar material in binary-accretion disk systems. Knowledge of these characteristics can provide important clues to the mechanism that drives the mass loss from the binary system and ultimately determines the system's evolutionary fate. My aim has been to quantify the polarimetric signatures of accretion disks in such systems, as a first step toward locating and describing the complex gas distributions that may accompany mass loss. As a test case, I have created detailed models of the eclipsing interacting binary β Lyr.; I first present spectropolarimetric measurements of β Lyr taken with the WUPPE ultraviolet spectropolarimeter and with the HPOL optical spectropolarimeter. Spectropolarimetry distinguishes between direct and scattered light in particular spectral features; studying the polarization behavior as a function of the orbital phase of a binary star helps locate scattering material within the system.; The questions raised by the spectropolarimetric analysis lead me to construct a three-dimensional modeling tool optimized for the simulation of polarization behavior in binary systems. The numerical Monte Carlo radiative transfer method is uniquely suited to interpreting polarization measurements in geometrically complex scenarios. Using the Monte Carlo code, I investigate the variation of key features in the polarization curve of a generalized binary-accretion disk system with the geometrical and optical properties of the disk.; Finally, I return to the case of β Lyr to apply the results of the Monte Carlo code to the observed V-band polarimetric behavior of this system. I constrain the disk opening angle and albedo, and find that the optical depth of the disk must vary with distance from the disk midplane. I also conclude that the polarization contributions from the mass-losing star and disk are not sufficient to reproduce the observed polarized light curve of β Lyr. This implies that the mass-gaining star, which does not contribute appreciably to the light curve of the system, must nevertheless be the source of a significant fraction of the total polarization of the system.