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Articles 1 - 30 of 57
Full-Text Articles in Astrophysics and Astronomy
Relativistic Transients From Compact Objects: Radiation Processes And Geometric Effects, Connery Chen
Relativistic Transients From Compact Objects: Radiation Processes And Geometric Effects, Connery Chen
UNLV Theses, Dissertations, Professional Papers, and Capstones
Relativistic transients from compact objects probe the most extreme regimes of physics, where strong gravity, ultra-relativistic outflows, and high-energy radiation operate simultaneously; understanding the underlying radiation mechanisms and extrinsic geometric and relativistic effects is essential for interpreting observations and constraining source properties. I develop theoretical and computational frameworks to quantify how geometry and relativistic motion shape observed emission from fast radio bursts, gamma-ray bursts, and neutron star mergers. I analyze fast radio bursts from the Galactic magnetar SGR J1935+2154 and show that emission geometry strongly governs burst energetics and detection probability, and influences the link between radio and X-ray emission. …
The Yorp Effect In Reboundx, Kaelyn Clement
The Yorp Effect In Reboundx, Kaelyn Clement
UNLV Theses, Dissertations, Professional Papers, and Capstones
The Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect is a radiation-induced torque that can affect the spin and rotational obliquity of small bodies. It has been observed to alter the rotation rate of asteroids in the Solar System (Lowry et al. 2007; Taylor et al. 2007). Under extreme circumstances, YORP can cause a body to fragment, inducing a cascade of fissions. This effect may be important in driving the pollution of white dwarf atmospheres in conjunction with other radiative forces. I developed a YORP calculator for REBOUNDX (Tamayo et al. 2020), an extensional library to the N-body integrator REBOUND (Rein & Liu 2012). I …
Fast Radio Bursts And Long Period Radio Transients: Radiation Mechanisms And Propagation Effects, Yuanhong Qu
Fast Radio Bursts And Long Period Radio Transients: Radiation Mechanisms And Propagation Effects, Yuanhong Qu
UNLV Theses, Dissertations, Professional Papers, and Capstones
Fast Radio Bursts (FRBs) are bright radio bursts with the highest brightness temperatures in the radio sky. In this thesis, we investigate the trigger mechanisms, radiation mechanisms, and propagation effects of FRBs. Two general classes of coherent radiation mechanisms are considered in two categories: pulsar-like models invoking emission originating within the magnetar magnetosphere, and GRB-like models, which attribute the emission to relativistic magnetized shocks occurring far away from the central engine. We use the general observed properties (polarization features and spectra bandwidths) of repeating FRBs to constrain the physical conditions needed for these two mechanisms. We propose that crust quakes …
The Origins Of Chondrite Families, Isabelle M. Perron
The Origins Of Chondrite Families, Isabelle M. Perron
UNLV Theses, Dissertations, Professional Papers, and Capstones
Chondrites, a type of primitive asteroid, are thought to have formed from dust and gas early in the life of our Solar System. These chondrites have remained unchanged since their formation, avoiding being melted or differentiated like other rocky bodies have. Due to this unique characteristic, chondrites can give us useful insight into how asteroids, planetesimals, and even the terrestrial planets formed. In order to study chondrites and their formation, I used code developed by Li et al. (2020), which utilizes thermodynamic code GRAINS (Petaev 2009), to see what conditions the chondrites may have originated from. GRAINS uses a variety …
The Compositional And Dynamical Properties Of Exoplanets, Cody James Shakespeare
The Compositional And Dynamical Properties Of Exoplanets, Cody James Shakespeare
UNLV Theses, Dissertations, Professional Papers, and Capstones
The solid surface density profile of protoplanetary discs, and the composition of these solids, can be formed through sequential condensation models of dust precipitating from the cooling gas of the solar nebula. I continue developing a code that reproduces the chemical compositions of most chondrites as well as the bulk compositions of the rocky planets using our partial condensation model with an evolving disc. I extend this validated code to exoplanet systems with different initial elemental ratios, like the carbon-to-oxygen ratio and estimated stellar abundances over the age of the universe. I have improved this dust condensation code to include …
Cross-Correlation Studies Of The Cosmological 21 Cm Signal And High-Redshift Galaxy Distributions, Simon Matin
Cross-Correlation Studies Of The Cosmological 21 Cm Signal And High-Redshift Galaxy Distributions, Simon Matin
UNLV Theses, Dissertations, Professional Papers, and Capstones
The Epoch of Reionization (EoR) marks a critical phase in cosmic history, during which time the first stars and galaxies ionized the surrounding neutral hydrogen gas. A powerful way to probe this period is by cross-correlating the 21 cm signal from neutral hydrogen with high-redshift galaxy distributions. In this study, we analyze the 21 cm-galaxy cross-power spectrum using simulated sky maps and explore its redshift evolution, revealing a transition from positive correlation at early times (high redshift) to anti-correlation at later stages of reionization (low redshift). Our results highlight the sensitivity of the cross-power spectrum to the evolving ionized structure …
On Efficient Position Dependent Computation Of Radiation Near Accretion Disks, Kara Jeanette Smith
On Efficient Position Dependent Computation Of Radiation Near Accretion Disks, Kara Jeanette Smith
UNLV Theses, Dissertations, Professional Papers, and Capstones
Accretion onto super massive black holes (SMBH) plays a vital role in explaining our observations of active galactic nuclei (AGN). One key aspect of observations of AGN is the prevalence of massive outflows which transport matter and energy away from the galactic core. These outflows are characterized by highly blueshifted absorption lines as radiation from the accretion disk is absorbed by gas which is moving toward us. Radiation pressure on spectral lines is expected to play a vital role in launching and accelerating these winds. At the other end of the spectrum of black hole masses, accretion disks in X-ray …
An Analysis Of The Propagation Of Gravitational Radiation Under A Graviton Of Nonzero Mass And Its Implications For Cosmological Measurements, Margaret Johnston
An Analysis Of The Propagation Of Gravitational Radiation Under A Graviton Of Nonzero Mass And Its Implications For Cosmological Measurements, Margaret Johnston
UNLV Theses, Dissertations, Professional Papers, and Capstones
Under the assumptions of General Relativity (GR), gravitational waves propagate at the speed of light and their mediation can be represented as a particle through a massless graviton. We investigate the impact and observability of the presence of a massive graviton, how such a modification to GR would also modify the observed gravitational waves from astrophysical sources, and how this effect can be used as an independent measurement of cosmmological parameters, including the Hubble parameter H0. We simulate the impact of a massive graviton on compact binary coalescence observation in a near-future LIGO-Virgo-KAGRA interferometer network through a modification to the …
Dynamical Studies Of Misaligned Circumbinary Disks, Ian C. Rabago
Dynamical Studies Of Misaligned Circumbinary Disks, Ian C. Rabago
UNLV Theses, Dissertations, Professional Papers, and Capstones
Binary stars are common outcomes of the star formation process, with nearly half of Sun-like stars forming as part of a binary pair. The presence of a second star adds additional complexity and dynamical effects to the planet formation process in the surrounding circumbinary disk. In this work, I investigate the behavior of a circumbinary disk using hydrodynamic modeling, specifically in the case where the disk is misaligned to the binary orbital plane. Around eccentric binaries, highly inclined disks can align themselves perpendicular to the binary orbital plane. These "polar disks'' can produce vortices and spiral arms when the disk …
Understanding Disk Substructures With 3d Self-Consistent Thermodynamics, Shangjia Zhang
Understanding Disk Substructures With 3d Self-Consistent Thermodynamics, Shangjia Zhang
UNLV Theses, Dissertations, Professional Papers, and Capstones
Protoplanetary disks are birthplaces of planets. The past decade witnessed a great advance- ment in disk observations by Atacama Large Millimeter Array (ALMA) and extreme adaptive optics (ExAOs). Hundreds of disks have been observed at high angular resolutions and revealed rich substructures (e.g., gaps/rings) at midplane and atmosphere, at least part of which are per- turbed by planets. Deep understanding of disk physics has a great potential to unveil more young planets from substructures and distinguish those that are not caused by planets. I worked on con- straining young planet populations using planet-disk interaction simulations and substructures and self-consistent treatment …
Climatic Influences On Incipient Alteration In Mars-Relevant Ultramafic Soils, Anthony Feldman
Climatic Influences On Incipient Alteration In Mars-Relevant Ultramafic Soils, Anthony Feldman
UNLV Theses, Dissertations, Professional Papers, and Capstones
An ongoing debate exists around the nature of the climatic conditions present during the Noachian and early Hesperian periods (~4.1 to 3 Gyr ago) of Mars’ ancient history. The various theories put forward can reasonably be grouped into “warm and wet” vs “cold and icy” camps. Warm and wet approximates an Earth-like system with a relatively clement climate with significant liquid water present including potentially long-lived oceans. Cold and icy theories generally postulate thick ice sheets at high elevations with periodic warming events driving precipitation and the formation of river channels and leading to the formation of chemical alteration products. …
Magmatic Processes Leading To Compositional Diversity In The Mars Crust, Amanda Marie Ostwald
Magmatic Processes Leading To Compositional Diversity In The Mars Crust, Amanda Marie Ostwald
UNLV Theses, Dissertations, Professional Papers, and Capstones
The ancient Mars crust can yield insights into planet formation and evolution that Earth cannot. Direct investigation of the martian surface is limited to studies on meteorites and rover-obtained analyses. The nakhlites and chassignites, two classes of martian meteorites, are together the largest suite of martian meteorites derived from a single location on the surface. As such, they present a rare opportunity to study the Mars crust in detail using samples bearing a contextual relationship. Rover studies have found a surprising amount of compositional diversity in surface materials, the formation mechanisms of which are not well-constrained. This dissertation leverages meteorites …
Joint Constraints On Kepler-36 From Kepler And New Keck-Hires Data, Nicholas Juliano
Joint Constraints On Kepler-36 From Kepler And New Keck-Hires Data, Nicholas Juliano
UNLV Theses, Dissertations, Professional Papers, and Capstones
I analyze new HIRES Radial Velocity (RV) data in conjunction with transit mid-times and uncertainties from the full 17 quarters of Kepler data to reassess the orbital parameters of the Kepler-36 system. Six additional RV measurements were taken by the Keck-HIRES spectrograph from September 21, 2021 to October 11, 2021. I carry out a differential evolution Markov Chain Monte Carlo-based (DEMCMC) analysis to infer improved orbital elements for the two known planets in the system. Leveraging additional information provided by the new RV measurements, I extend this DEMCMC analysis to a possible three-planet configuration. I explore the likelihood of a …
Simulating Radial Ring Structure With An Ambipolar Elsasser (Am) Bump In Non-Ideal Magnetohydrodynamics Of Protoplanetary Disks, Aleksey S. Mohov
Simulating Radial Ring Structure With An Ambipolar Elsasser (Am) Bump In Non-Ideal Magnetohydrodynamics Of Protoplanetary Disks, Aleksey S. Mohov
UNLV Theses, Dissertations, Professional Papers, and Capstones
Rings are one of the most ubiquitous substructures observed in protoplanetary disks. They are known to be a robust site for planetesimal formation; thus we look for mechanisms that can originate stable rings. From chemical modelling of snow lines, we expect a bump in the Ambipolar Diffusion (AD) Elssaser number (Am) in the radial direction. We use the Athena++ code to model the non-ideal Magentohydrodynamics (MHD) behavior of an Am bump. We explore a parameter space of Gaussian bumps with Am = 5, 1, 0.5 peak strength and σ = 0.25, 1, 5. The Gaussian profile is inserted into the …
The Response Of Atomic-To-Molecular Hydrogen Transition Points In Photodissociation Regions Due To A Hard X-Ray Spectrum, Gregory Joseph Colarch
The Response Of Atomic-To-Molecular Hydrogen Transition Points In Photodissociation Regions Due To A Hard X-Ray Spectrum, Gregory Joseph Colarch
UNLV Theses, Dissertations, Professional Papers, and Capstones
This dissertation develops a model for the response of the transition points in the density profiles from atomic (H0) to molecular (H2) hydrogen in a photodissociation region (PDR) due to a hard X-ray flux (HXR). A model for a steady-state PDR due to the photodissociation of H2 by the far-ultraviolet (FUV) Lyman-Werner radiation band is presented both analytically and computa- tionally. A steady state X-ray dissociation region (XDR) from an HXR in the 1 - 100 keV energy range is also developed both analytically and computationally. An analytic model is then developed by combining these two different steady state models. …
On Outflows Due To Radiation, Randall Cody Dannen
On Outflows Due To Radiation, Randall Cody Dannen
UNLV Theses, Dissertations, Professional Papers, and Capstones
Observations of ionized AGN outflows have provided compelling evidence that the radiation field transfers both momentum and energy to the plasma. At parsec scale distances in AGN, energy transfer can dominate, in which case the only force needed to launch an outflow is due to gas pressure. Much closer to the black hole, gravity dominates thermal energy due to insufficient heating by the radiation and the gas is in the so-called ’cold wind solution’ regime. Only magnetic or radiation forces can lead to outflow, but it is unclear how these forces depend on the spectral energy distribution (SED) and the …
Inferring The Compositions And Interior Structures Of Small Planets, David R. Rice
Inferring The Compositions And Interior Structures Of Small Planets, David R. Rice
UNLV Theses, Dissertations, Professional Papers, and Capstones
Although there are now over 10,000 confirmed and candidate extrasolar planets, accurate masses and radii have been determined for around 200 planets of less than 10 Earth-masses. This number will grow exponentially over the next decade as extreme precision radial velocity spectrographs see first light. The densities of small planets hint at a diverse range of compositions for terrestrial worlds from super-Mercuries to super-Ganymedes. Uncertainty in density is as low as 3% in the Trappist-1 system. To determine composition from observed parameters, the community uses a variety of interior structure models. Underlying these models are multiple computational techniques, numerous experimental …
Transient Sources And How To Study Them: Selected Topics In Multi-Messenger Astronomy, Jiawei Luo
Transient Sources And How To Study Them: Selected Topics In Multi-Messenger Astronomy, Jiawei Luo
UNLV Theses, Dissertations, Professional Papers, and Capstones
The discovery of cosmic neutrino flux by IceCube, and the multi-messenger observations of gravitational event GW170817 ushered in the era of multi-messenger astronomy. Since the Universe itself is a natural laboratory, multi-messenger astronomy can help us study the most extreme physics processes in great detail. In this dissertation, we touch on some of the currently unanswered questions involving different types of transient sources and different “messengers” of multi-messenger astronomy. We employ a variety of analysis methods, including machine learning, a method that has not yet been widely adopted in astronomy but is rapidly gaining momentum.We start this dissertation with Chapter …
Day ‘N’ Nite: Habitability Of Tidally Locked Planets With Sporadic Rotation, Cody James Shakespeare
Day ‘N’ Nite: Habitability Of Tidally Locked Planets With Sporadic Rotation, Cody James Shakespeare
UNLV Theses, Dissertations, Professional Papers, and Capstones
Tidally locked worlds provide a unique opportunity for constraining the climates of detected exoplanets. They are unique in that few exoplanet spin and obliquity states are known or will be determined in the near future. The TRAPPIST-1 exoplanet system has multiple habitable zone planets that, in the past, have been presumed to be tidally locked. However, a recent study shows the dynamical conditions present in the TRAPPIST-1 system make rotation and large librations possible spin states for these planets. I confirm the tendency for these planets to sporadically transition from tidally locked libration to slow rotation using N-body simulations independent …
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 …
Physics Of Electromagnetic Counterparts Of Binary-Neutron-Star Mergers, Shunke Ai
Physics Of Electromagnetic Counterparts Of Binary-Neutron-Star Mergers, Shunke Ai
UNLV Theses, Dissertations, Professional Papers, and Capstones
Binary neutron star (BNS) mergers are supposed to be the sources of a variety of astrophysical transients, including both gravitational wave (GW) and electromagnetic (EM) signals. The types and properties of the post-merger central product contain crucial information for many unsolved physical problems. Since the current GW detectors are not sensitive enough in kHz, only GWs from the inspiral phase can be detected, so that one cannot directly study the central products from GWs. EM signals can serve as probes to infer the type and properties of the central product. When a long-lived neutron star (NS) is formed after the …
Dust-Gas Dynamics Driven By The Streaming Instability With Various Pressure Gradients, Stanley Antedio Baronett
Dust-Gas Dynamics Driven By The Streaming Instability With Various Pressure Gradients, Stanley Antedio Baronett
UNLV Theses, Dissertations, Professional Papers, and Capstones
The radial pressure gradient (RPG), along the midplane of gaseous protoplanetary disks (PPD) – planetary nurseries – poses a severe obstacle to planet formation. Micron-sized dust grains, embedded in the disc, must quickly grow to kilometer-sized planetesimals – the building blocks of planets – before fatally drifting inwards, by RPG-induced gas drag, into a central host star. However, the RPG simultaneously powers one of the most robust processes to overcome this radial-drift barrier: the streaming instability (SI). Spontaneously triggered, the SI aerodynamically concentrates drifting dust via drag-induced, coupled interactions and feedback with the surrounding gas. In particular, the non-linear phase …
The Effects Of Winds On Accretion Disks And Spectra Of X-Ray Binaries And Active Galactic Nuclei, Shalini Ganguly
The Effects Of Winds On Accretion Disks And Spectra Of X-Ray Binaries And Active Galactic Nuclei, Shalini Ganguly
UNLV Theses, Dissertations, Professional Papers, and Capstones
Active galactic nuclei (AGNs) and X-ray binaries (XRBs) contain at their cores supermassive black holes (SMBH), and stellar mass black holes or neutron stars, respectively. These objects bind matter gravitationally, leading to the formation of accretion disks. The accretion of matter leads to efficient conversion of gravitational potential energy into radiation. When the force and/or energy imparted by this radiation on matter exceeds the attractive force due to the local gravitational field, it leads to the launching of matter in the form of outflows or winds. These outflows produce blueshifted (and occasionally redshifted) emission or absorption components in the spectra …
Miocene Ichnofaunas And Mammalian Communities In The Great Basin Region, Nevada And California, Annmarie R. Jones
Miocene Ichnofaunas And Mammalian Communities In The Great Basin Region, Nevada And California, Annmarie R. Jones
UNLV Theses, Dissertations, Professional Papers, and Capstones
The purpose of this dissertation is to document and interpret three new ichnofaunas and two fossil assemblages from the Neogene of Nevada and California. Ichnofossils are important for understanding behavior and geographical range of animals in the distant past and are key to locating and preserving sensitive material for future studies. I examined ichnofauna at three localities: two within the Mio-Pliocene Muddy Creek Formation of Nevada, and one within the Miocene China Ranch Beds of California. My research focuses primarily on (1) camelid and ursid ichnotaxa and how these new localities help in understanding the evolutionary history of these taxa …
Viability Of Energy And Fuel Sources For Interstellar Travel; Design And Feasibility Of The Construction Of Manned Interstellar Space Shuttles, Lukas Mittelman
Viability Of Energy And Fuel Sources For Interstellar Travel; Design And Feasibility Of The Construction Of Manned Interstellar Space Shuttles, Lukas Mittelman
UNLV Theses, Dissertations, Professional Papers, and Capstones
The importance of proving the viability of interstellar transport and addressing its potential hazards and pitfalls is immense. If we do not look toward the future and examine what could be waiting for us, we are doing our children, our children’s children, and so on, a disservice. Here we must attempt to lay the groundwork for our future scientists, engineers, and adventurers. Asking and answering questions like, which propulsion and energy systems must we incorporate to send us through the cosmos? Will we utilize technologies known today, such as fossil fuel rockets, fission or fusion rockets, and antimatter drives (pion …
Terrestrial Planet Formation In M-Dwarf And Binary Star Systems, Anna C. Childs
Terrestrial Planet Formation In M-Dwarf And Binary Star Systems, Anna C. Childs
UNLV Theses, Dissertations, Professional Papers, and Capstones
I examine circumbinary terrestrial planet formation in a gas free environment around various binary systems and terrestrial planet formation in a gaseous environment around M-dwarfs. While terrestrial cirumbinary planets have yet to be observed, this is likely due to observational bias. Motivated by recent observations of highly misaligned circumbinary gas disks, I perform a suite of n-body studies to understand the properties of terrestrial planets around various binary systems. In a polar alignment, a circumbinary disk is inclined by 90 degrees relative to the binary orbital plane. I find that terrestrial planet formation in a polar configuration may be as …
Orbital Dynamics And Stability Of Circumbinary Planetary Systems And Small Bodies In The Solar System, Cheng Chen
Orbital Dynamics And Stability Of Circumbinary Planetary Systems And Small Bodies In The Solar System, Cheng Chen
UNLV Theses, Dissertations, Professional Papers, and Capstones
My main research focuses on the dynamics and stability of circumbinary planetary systems and of small bodies in the solar system. Unlike the two-body problem, the three-body problem is more complex as there are stronger interactions with two massive bodies in the system. In the outer solar system, the apsidal precession secular resonance with Neptune makes comets in the Kuiper belt unstable in the early stages of the solar system. This resonance a likely origin for the nitrogen-delivering comets that impacted the Earth bringing some of the nitrogen in the Earth’s atmosphere today. Beyond the solar system, we have observed …
Accretion And Debris Disc Dynamics Around Single And Higher-Order Star Systems, Jeremy L. Smallwood
Accretion And Debris Disc Dynamics Around Single And Higher-Order Star Systems, Jeremy L. Smallwood
UNLV Theses, Dissertations, Professional Papers, and Capstones
My research deals with highly topical areas of astrophysics, such as planet habitability, stellar evolution, the origin of fast radio bursts, the evolution of debris discs, and the dynamics of accretion discs in binary and higher-order star systems. Accretion discs around binary star systems are ubiquitous in the galaxy and planet formation is thought to occur within these discs. Circumbinary discs are commonly observed to be misaligned with respect to the binary orbital plane. A misaligned circumbinary disc eventually evolve to a stable orientation, either coplanar or polar with the binary orbital plane. The process of disc alignment has important …
Constraining Viscous Protoplanetary Disk Models Using Alma Kinematic Observations, Ian Rabago
Constraining Viscous Protoplanetary Disk Models Using Alma Kinematic Observations, Ian Rabago
UNLV Theses, Dissertations, Professional Papers, and Capstones
Recent molecular line observations by ALMA have revealed the 3D velocity structure of protoplanetary disks, providing new insight on the mechanisms of disk accretion and ring/gap formation. Although the constant α viscous disk model has been widely used to describe the disk surface density evolution, it may not adequately describe the gas velocity at different disk heights. By carrying out viscous hydrodynamic simulations, we confirm that the vertical velocity structure varies considerably between these models. On the other hand, the surface density evolution of the disk is only dependent on the vertically integrated stress, and does not depend on a …
The Timing Of Dynamical Interactions Between Planets In Exoplanetary Systems, David Robert Rice
The Timing Of Dynamical Interactions Between Planets In Exoplanetary Systems, David Robert Rice
UNLV Theses, Dissertations, Professional Papers, and Capstones
During the late stage of planet formation, a system is often dynamically packed with protoplanets. These bodies collide together and are ejected from the system to form the final planets. The duration of stability before these dynamical interactions occur is dependent on the initial separation of the bodies in a system. Previous works have shown that the time before a planet-planet close encounter is exponential with the initial planet spacing measured in units of mutual Hill radius. We investigate the limitations of these previous studies. We find that systems that are initially similar can have larger differences in stability times …