Doctor of Philosophy, University of Toledo, 2020, Physics

Be stars are rapidly rotating B stars whose spectra contain Balmer emission lines originating from circumstellar decretion disks. The decretion disks also produce in- frared (IR) excesses in their spectral energy distributions, and the slope of the excess reveals information about the density of the disk. The decretion disks serve as medi- ums through which mass and angular momentum are transported away from the star. Be stars rotate at or near the critical rotation rate, and the angular momentum lost through the disks prevents them from breaking up. Determinations of the amount mass and angular momentum lost through the decretion disks are model dependent. The best accepted model describing the decretion disk is the Viscous Decretion Disk (VDD) model. However, there is a discrepancy between the current measurements of mass-loss rates and those predicted by stellar evolutionary models. The projects in this thesis were chosen to better constrain the models in an effort to reconcile this discrepancy. First, it has been suggested that Be stars are spun up through previous mass- transfer from a binary companion. Also, binary companions are observed to be common. However, the VDD model assumes an isolated Be star. In this thesis, I investigate the density structure of the disks in the presence of binary companions. The Be disk is truncated by the companion, and while most of the disk material accretes onto the binary companion, we find that a portion flows past the binary in what is likely a wind-like outflow. Second, the radiation from the central Be star can launch a line-driven ablation wind that flows radially outward along the surface of the disk. This disk wind is an additional source of mass and angular momentum loss from the central star. I investigate how the disk wind would be observed in the ultraviolet (UV) wind line profiles. I find that the disk wind can be seen as a low velocity narrow absorption component in the UV wind line when the observing geome (open full item for complete abstract)

Committee: Jon Bjorkman (Committee Chair); Alex Carciofi (Committee Member); Michael Cushing (Committee Member); Scott Lee (Committee Member); Tom Megeath (Committee Member) Subjects: Astronomy; Astrophysics

PhD, University of Cincinnati, 2018, Arts and Sciences: Physics

In this thesis we present the composite results of our Monte Carlo radiative transfer modeling for three circumstellar disk systems: PDS 70, HD 100453, and HD 100546. For each of these systems we produced models which reproduce the observational imagery while simultaneously fitting the SED. We focus primarily on probing the detailed structure of these disks and putting constraints on their overall structure and composition. In addition we present a discussion of Monte Carlo techniques and common problems encountered in modeling.

Committee: Michael Sitko Ph.D. (Committee Chair); Philip Argyres Ph.D. (Committee Member); F Paul Esposito Ph.D. (Committee Member); Margaret Hanson Ph.D. (Committee Member) Subjects: Astrophysics