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An Investigation Of The Accretion Processes In T Tauri And Herbig Ae/Be Systems Using High Resolution Optical And Near-Infrared Spectroscopy, Joshua Kern
All Dissertations
Star and planet formation is intimately tied to the accretion of material from the environments in which they form. During the formation process, disks of gas and dust develop in young stellar objects through which material is facilitated to the star and forming planets. Theoretical models of these accretion processes invoke viscous spreading via hydrodynamics, as well as more complex interactions with magnetic fields be it from the stellar component or the formation environment in order to catalyze these mass flows. These accretion models predict various scenarios including magnetospheric accretion as well as supersonic accretion flows in the disk atmosphere …
Simulating The Eccentricity Evolution Of Accreting Equal-Mass Binaries: Numerical Sensitivity To The Computational Domain Size And Grid Resolution, Zhongtian Hu
All Theses
With high resolution hydrodynamics simulations, we show that the optimal values of domain radius and grid resolution for the software Sailfish when simulating time-based eccentricity evolution of equal mass, non-circular accreting binaries in a circumbinary disk to be $r_{\rm out} \leq 15a$ and $\delta x / a \le 0.01 $. These values provide a useful guideline for optimizing the performance of simulation runs while maintaining scientific accuracy. Each artificial parameter is probed with 15 runs of 2000 orbits each.
Evaluating Neutron Star Binding Energies Using Rotating Accreting Models, Nathan Moore
Evaluating Neutron Star Binding Energies Using Rotating Accreting Models, Nathan Moore
Honors Theses
Neutron star binding energy increases due to accreting matter from neighboring astronomical bodies, and decreases due to the star spinning up, increasing its angular velocity. We present a novel set of models that account for both increasing angular velocity and accreting matter to track a neutron star’s evolution. We arrive at these models through studying and reconfiguring computational investigations from the past, particularly a code which generates a model for a given fixed baryon mass and angular velocity and another that takes it from one baryon mass and angular velocity to the next one through accretion, to obtain a full …
Polar Alignment Of Massive Retrograde Circumbinary Discs, Charles Abod
Polar Alignment Of Massive Retrograde Circumbinary Discs, Charles Abod
UNLV Theses, Dissertations, Professional Papers, and Capstones
To understand the observed circumbinary planetary systems, we must first explain the dynamics of the circumbinary discs in which they formed. Observations of circumbinary discs show that misalignments to the binary orbital plane may be common. Here we investigate these systems by exploring the orbital dynamics of three-body systems and circumbinary discs. A test particle orbit around an eccentric binary has two stationary states in which there is no nodal precession: coplanar and polar. Nodal precession of a misaligned test particle orbit centres on one of these stationary states. A low mass circumbinary disc undergoes the same precession and moves …
Accretion Onto Endoparasitic Black Holes At The Center Of Neutron Stars, Chloe B. Richards
Accretion Onto Endoparasitic Black Holes At The Center Of Neutron Stars, Chloe B. Richards
Honors Projects
We revisit the system consisting of a neutron star that harbors a small, possibly primordial, black hole at its center, focusing on a nonspinning black hole embedded in a nonrotating neutron star. Extending earlier treatments, we provide an analytical treatment describing the rate of secular accretion of the neutron star matter onto the black hole, adopting the relativistic Bondi accretion formalism for stiff equations of state that we presented elsewhere. We use these accretion rates to sketch the evolution of the system analytically until the neutron star is completely consumed. We also perform numerical simulations in full general relativity for …
Reflection And Reverberation In Neutron Star Low-Mass X-Ray Binaries, Benjamin Coughenour
Reflection And Reverberation In Neutron Star Low-Mass X-Ray Binaries, Benjamin Coughenour
Wayne State University Dissertations
Neutron star low-mass X-ray binaries (NS LMXBs) are systems which consist of a NS and a low-mass companion star. They are naturally variable on a variety of timescales, and are even classified by their X-ray spectral variability on the timescales of hours to days. The most luminous NS LMXB sources are known as ‘Z’ sources, because they trace out a characteristic ‘Z’ shape when plotted on a color-color or hardness-intensity diagram. The physical mechanisms causing this variability are not well understood. To try to address this, we model spectra taken from different positions on a hardness-intensity diagram of two Z …
Correlation Between Emission Lines And Radio Luminosities Of Active Galactic Nuclei, Jessica Short-Long
Correlation Between Emission Lines And Radio Luminosities Of Active Galactic Nuclei, Jessica Short-Long
Theses and Dissertations--Physics and Astronomy
Radio-loud active galactic nuclei (AGN) are one class of objects associated with accretion activity onto supermassive black holes in centers of massive galaxies. They are believed to be in a radiatively-inefficient accretion mode with low accretion rate. To understand this accretion mode, it is important to measure its radiative output at high energies (> 13.6eV), which can be traced through optical emission lines. However, little is known about their true radiative output. This is because no correlation between optical emission-line and radio luminosity has been found for the majority of low-luminosity radio AGN, which are often classified as low-excitation radio …
The Formation Of Fine-Grained Chondrule Rims In Unequilibrated Ordinary Chondrites, John Bigolski
The Formation Of Fine-Grained Chondrule Rims In Unequilibrated Ordinary Chondrites, John Bigolski
Dissertations, Theses, and Capstone Projects
Fine-grained rims are ubiquitous, non-igneous, features that completely or partially envelope the majority of chondrules within the least equilibrated of the unequilibrated ordinary chondrites (UOCs). A detailed examination of such rims in 4 UOC samples less than petrologic type 3.2 was conducted in order to 1) characterize the relative distribution of rims within chondrite samples, 2) inspect differences between fine-grained rims and adjacent matrix material, 3) petrologically analyze the rims and their relationships with chondrule cores, 4) characterize an ungrouped UOC, Northwest Africa 5717, 5) conduct a microanalytical investigation of rim / matrix boundaries to discern relative chronologies of fine-grained …
Star-Disk Interaction In Herbig Ae/Be Stars, Christa Speights
Star-Disk Interaction In Herbig Ae/Be Stars, Christa Speights
All Theses
The question of the mechanism of certain types of stars is important. Classical T Tauri (CTTS) stars accrete magnetospherically, and Herbig Ae/Be stars (higher-mass analogs to CTTS) are thought to also accrete magnetospherically, but the source of a kG magnetic field is unknown, since these stars have radiative interiors. For magnetospheric accretion, an equation has been derived (Hartmann, 2001) which relates the truncation radius, stellar radius, stellar mass, mass accretion rate and magnetic field strength.
Currently the magnetic field of Herbig stars is known to be somewhere between 0.1 kG and 10 kG. One goal of this research is to …
Time-Series Observations Of The High Mass X-Ray Binary 4u 2206+54 To Monitor Light Variation, Jessica Lynn Bugno
Time-Series Observations Of The High Mass X-Ray Binary 4u 2206+54 To Monitor Light Variation, Jessica Lynn Bugno
Theses and Dissertations
The high mass X-ray binary 4U 2206+54 has been a very controversial system due to variability in spectral data as well as photometric data. We, at Brigham Young University, have been observing this system in multiple filters with several telescopes. This thesis presents our methods of observations, reductions, and results. It also compares what we have been detecting to other groups looking at the same target in different wavelengths. Furthermore, this thesis discusses some of the peculiarities of 4U 2206+54 and possible theories to explain these phenomena. Based on our photometric observations for the past three years, we believe the …
Fuor And Exor Variables: A Nir High-Resolution Spectroscopic Survey, Joseph Liskowsky
Fuor And Exor Variables: A Nir High-Resolution Spectroscopic Survey, Joseph Liskowsky
All Theses
To better understand the labyrinth of heating and cooling processes in YSOs (young stellar objects), we study systems where there exists a large variability in the heating of this gas due to accretion. This research project focuses on several classes of early young eruptable T-Tauri stars, namely the FUors, the EXors and the so-called FU Ori-like, which all have the property of large amplitude oscillations in accretion rate. Each of these categories may well represent specific stages in early low-mass stellar evolution. While these objects have specific spectroscopic and circumstellar diagnostics (as means of identification) our research suggests that there …