Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Astronomy

Supervisor

Dr. Carol E. Jones

Abstract

Classical Be stars are rapidly-rotating, massive stars that exhibit distinct observational characteristics due to the presence of enveloping, equatorial disks of gas. While diligent observation of these objects has established a reliable description of their geometric and kinematic properties, our understanding of classical Be stars remains distressingly limited on the dynamical front. Principally, we lack a satisfactory characterization of the physical process(es) through which the gaseous disks form and dissipate. In order to understand the mechanisms that govern the development of these enigmatic stars, we use computational codes to produce theoretical models of these objects and their environments. We compare the predicted observables to astronomical observations of classical Be stars. By interpreting the results of these comparisons, we can place important constraints on the parameters of the models, and thus determine fundamental properties of the circumstellar disks.

The intrinsic continuum linear polarization signature is a distinguishing feature of classical Be stars. Arising from electron scattering in the non-spherically symmetric distribution of gas, this signature provides a unique means for directly probing the physical and geometric properties of the circumstellar environment. In this thesis, we assess the potential role of polarimetry in investigating the dynamical nature of classical Be star disks. We present our implementation of a Monte Carlo computation of the Stokes intensities using the self-consistent thermal solution of a non-LTE radiative transfer code. We highlight the relative importance of multiple-scattering and disk temperature in predicting the fraction of linearly polarized light emerging from classical Be stars. We also demonstrate that gas metallicity has a minimal effect in the determination of the degree of linear polarization. Finally, by demonstrating that the principal features of the polarimetric signature originate from different parts of the disk, we illustrate how these properties can have an important role in characterizing both the geometric nature and the evolution of the disk. This work establishes a critical understanding of how the continuum linear polarization signature forms and how we can interpret it in the context of the dynamics of classical Be star disks.


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