Thesis Format
Integrated Article
Degree
Doctor of Philosophy
Program
Physics
Supervisor
Jones, Carol E.
Abstract
Classical B-emission stars (Be stars) are rapidly rotating B-type stars that form a gaseous circumstellar disk. As Be star disks evolve on human timescales of months to years unlike other astrophysical objects, they are excellent testbeds for studying the evolution, and testing our understanding, of astrophysical disks. In this thesis, I utilize and combine three-dimensional (3D) computation techniques to study the dynamical evolution and observational changes of Be star disks in systems with a binary companion whose orbit is misaligned to the initial plane of the disk.
I first use a 3D smoothed particle hydrodynamics (SPH) code to simulate the growth and dissipation of Be star disks in equal-mass binary systems with a misaligned binary orbit, and find some disks undergo phenomena of Kozai-Lidov oscillations, or disk tearing. I then perform a separate study using the three-dimensional Monte Carlo radiative transfer code, HDUST, to examine the differences in disk temperature, ionization, and resulting observables, of a disk tilted out of the equatorial plane versus a typical non-tilted disk. I show that a tilted disk has a non-axisymmetric temperature structure, and that a tilted disk is best detected via a change in the polarization position angle. I then developed an interface to allow output of SPH to be used as input into HDUST, and use said interface to predict observables of a tearing disk. I show that the long-term trends in the tearing disk model are the best match yet to the trends observed in the Be star Pleione (28 Tau). In the final work I expand the suite of SPH simulations to lower mass ratios and different viscosity values to show that Kozai-Lidov oscillations and disk tearing can occur for a range of system parameters, and also present predicted observables of a disk while it goes through Kozai-Lidov oscillations. I also show that a torn disk, or a disk with Kozai-Lidov oscillations, can be detected through changes in an interferometric visibility curve. I conclude by discussing the impact of these results and how these computational advancements can be utilized and expanded upon in future research of astrophysical disks.
Summary for Lay Audience
Disk-like structures are prevalent throughout the universe, from disks of stars, dust, and gas that make up galaxies, to disks of material being pulled into a black hole, or to disks of material around new stars that eventually form planets like those in our Solar System. This makes understanding the behaviour of astrophysical disks, and the processes that govern their evolution, of utmost importance.
My research focuses on a type of massive star called B-emission stars (Be stars), that rapidly rotate and grow a disk of gas around themselves. As these disks evolve on human timescales of months to years unlike other astrophysical objects, they are excellent testbeds to study the properties of disks. Be stars are also frequently found to be in orbit with a second (binary) star, and it is thought that material lost from this binary companion contributes to the rapid rotation of the Be star, which then allows the disk to grow.
My work in this thesis uses three-dimensional (3D) computational techniques to model Be star disks where a binary star has an orbit that is not in the same plane as the disk. Using a technique called smoothed particle hydrodynamics (SPH), I model the evolution of Be star disks, and find that sometimes the misaligned binary orbit can cause the disk to tear into two distinct pieces, or undergo a special type of oscillation called Kozai-Lidov oscillations, where the disks inclination and eccentricity oscillate. Next, I create static 3D models using a code which is able to follow how light propagates through the disk, to predict how disks would look to our telescopes if they are tilted, torn, or undergoing Kozai-Lidov oscillations. Through comparing with many years of real-world data, I find that the Be star known as Pleione seems to be undergoing disk tearing about every 34 years.
My work has produced the first fully 3D models of Be star disks that predict observables as they evolve over time. The computational advancements presented in this thesis will be able to be applied to many other systems and scenarios in the near and far future.
Recommended Citation
Suffak, Mark W., "Be Stars in Misaligned Binary Systems" (2025). Electronic Thesis and Dissertation Repository. 10708.
https://ir.lib.uwo.ca/etd/10708
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.
