Astrophysics and Astronomy Commons^™

Extreme Geomagnetic Storm Effects On Earth's Radiation Belts Observed By Calet On The International Space Station, Anthony W. Ficklin

LSU Doctoral Dissertations

This dissertation examines changes in Earth's energetic-particle environment using measurements from the Calorimetric Electron Telescope (CALET) on the International Space Station. Although CALET was designed primarily for high-energy cosmic-ray and gamma-ray observations, its count rates provide nearly continuous measurements of particles of ~1 MeV and above. The analysis uses the CHDX, CHDY, and IMC4X channels, which have approximate electron thresholds of $>\!1.5$, $\!>3.4$, and $\!>8.2$~MeV and proton thresholds of $>\!17$, $\!>37$, and $\!>52$~MeV, respectively. Because these measurements do not identify particle species, the observations are interpreted using their geographic and geomagnetic distributions, the relative …

Scattered Light Noise At Ligo Livingston Observatory Induced By Microseismic Ground Motion, Debasmita Nandi

LSU Doctoral Dissertations

Gravitational waves are “ripples” in the fabric of spacetime and create a minuscule change in the distance between two points. After publishing his theory of general relativity in 1915, Albert Einstein predicted the existence of gravitational waves as a consequence of the theory. Almost 100 years after the theoretical prediction, gravitational waves were detected for the first time in 2015 by the Advanced LIGO detectors in Livingston, Louisiana, and Hanford, Washington. Gravitational waves have a very small amplitude, making it very challenging to detect them. Different types of noise sources either of instrumental or environmental origin can reduce the astrophysical …

Measurement Of 18f(Alpha,P)21ne With The Array For Nuclear Astrophysics And Structure With Exotic Nuclei (Anasen), Keilah S. Davis

LSU Doctoral Dissertations

Certain (α,p) reactions on proton-rich nuclei are among the most important nuclear reactions occurring during Type I X-ray bursts, as well as being impactful in stellar explosions during the Asymptotic Giant Branch (AGB) phase and on accreting white dwarfs (WD). However, large uncertainties remain for reaction rates on some radioactive nuclei due to the lack of direct measurements. The Array for Nuclear Astrophysics and Structure with Exotic Nuclei (ANASEN) is a gas target and charged-particle detector designed for direct measurements of (α,p) reactions. ANASEN was redesigned with two hexagonal barrels of 100-µm-thick silicon strip surrounding the beam axis over a …

Determining The 17f(Α,P)20ne Reaction Rate For Application In Type I X-Ray Bursts, William Braverman

LSU Doctoral Dissertations

The ¹⁷F(α, p)²⁰Ne reaction has been identified as an alternate pathway for breakout from the hot-CNO cycle that can be important in some X-ray burst scenarios. The ¹⁷F(α, p)²⁰Ne reaction rate was previously determined through a parameterized exponential S-factor with a large enhancement from thermally-excited states based on statistical models with large uncertainties. We have measured the time-inverse ²⁰Ne(p,α)¹⁷F cross section at center-of-mass energies ranging from 5.50 to 7.10 MeV using an activation method with a proton beam on a neon gas cell. Coincident detections of 511-keV γ-rays, resulting from electron-positron …

Dose Characterization Of Galactic Cosmic Rays In The Human Brain: A Phits-Based Study With A Segmented Anatomical Phantom, Shanice N. Manning

LSU Master's Theses

Astronauts aboard the International Space Station (ISS) are chronically exposed to a complex space radiation environment composed of galactic cosmic rays (GCR), solar particles, and Earth's trapped radiation. These high-energy particles interact with spacecraft shielding, producing secondary particles that can penetrate inside and deposit energy in sensitive tissues. Although animal studies have been useful in assessing space radiation risks, anatomical and physiological differences limit their applicability to human anatomy especially neuroanatomy. To address this gap, we developed a computational framework to model radiation dose distribution within the human brain using Monte Carlo simulations in Particle and Heavy Ion Transport code …

The Search For Magnetar Giant Flares In Archival Gamma-Ray Burst Data To Constrain Their Rates And Energetics, Aaron Trigg

LSU Doctoral Dissertations

Magnetar giant flares are rare, extremely bright bursts of gamma-rays from highly magnetized neutron stars. These events are difficult to identify because, at extragalactic distances, they can appear similar to other astrophysical phenomena. Only a handful have been confidently identified to date, limiting our understanding of their origin and physical properties. This dissertation focuses on expanding the sample of known events and enabling a more detailed characterization of their observational features. We report on two newly identified examples, GRB 180128A and GRB 231115A, that are consistent with a magnetar origin based on their spectral properties and association with nearby star-forming …

19ne Excited States In Explosive Nucleosynthesis, Khang Pham

LSU Doctoral Dissertations

Classical novae and Type I X-ray bursts are stellar explosions that occur in binary systems, where nuclear reactions involving ¹⁹Ne play a crucial role in nucleosynthesis. In novae, the destruction of ¹⁸F via the ¹⁸F(p,alpha)¹⁵O reaction significantly affects the amount of ¹⁸F remaining in the ejecta, directly influencing the detectability of predicted 511-keV gamma rays. However, discrepancies between observed and predicted ¹⁸F abundances highlight uncertainties in the reaction rates, primarily due to unknown properties of resonances in the compound nucleus ¹⁹Ne. In Type I X-ray bursts, the ¹⁵O(alpha,gamma)¹⁹Ne reaction …

Optical Spring Tracking For Enhancing Quantum-Limited Interferometers, Scott M. Aronson

LSU Doctoral Dissertations

Gravitational waves were first predicted by Albert Einstein in 1916. Calculations in the 1970s by Rainer Weiss showed an interferometer of sufficient size could realistically detect gravitational waves, which led to a grant by the National Science Foundation (NSF). With steady progress and over decades of funding by the NSF, the construction of two full scale 4km interferometers was approved and began construction in 1994. This project, coined LIGO the Laser Interferometer Gravitational-wave Observatory, came to be a worldwide collaboration of scientists dedicated to the discovery and study of gravitational waves. In 2015, both LIGO detectors detected a coincident inspiral …

Constraining Giant Planet Occurrence Rates With The Multi-Band Imaging Survey For High-Alpha Planets (Mishaps) Observations Of 47 Tucanae, Alison Crisp

LSU Doctoral Dissertations

Though the confirmed exoplanet population has now reached over 5,500 planets, we still have a plethora of unanswered questions, e.g., regarding their formation mechanisms, true demographics, occurrence rates, and habitability. One remaining question is whether hot Jupiters formed in situ or migrated to their current orbits, so close to their host stars that their periods are 10 days or less. This question can potentially be answered by probing the effects of elemental abundances on hot Jupiter occurrence rates. These rates have been found to correlate with metallicity, but the specific elements responsible for the correlation have largely been unresolved. The …

Characterizing And Mitigating Transient Noise In Ligo Observatories For Gravitational Wave Detection, Jane Glanzer

LSU Doctoral Dissertations

The existence of gravitational waves is predicted by Albert Einstein's Theory of General Relativity. Commonly referred to as "ripples in spacetime", these waves are generated by some of the most violent and energetic processes in the universe. Despite their theoretical prediction over a century ago, it wasn't until 2015 that the Advanced LIGO (aLIGO) interferometers in Hanford, WA and Livingston, LA directly detected gravitational waves for the first time, confirming Einstein's theory and ushering in a new era of astrophysics.

Detecting gravitational waves requires incredible precision. Because of the extreme sensitivity required, it is possible for the gravitational wave data …

Connecting The Optical Regime To The X-Ray In Neutron Star Low Mass X-Ray Binaries, Alexander B. Igl

LSU Doctoral Dissertations

Using Rossi X-Ray Timing Explorer and Otto Struve Telescope data of low mass X-ray binaries (LMXBs) Cyg X-2 and Sco X-1, the optical regime’s relationship to the X-ray was investigated through several angles. Discrete cross correlations using the optical and X-ray data revealed evidence of reprocessing in both datasets. These were more consistently present in Sco X-1, where both small and obvious features were seen at less than 4 s of optical lag. The size of these lags makes it likely that most of the reprocessing is taking place on the accretion disk. Parameterization of the Z tracks led to …

Analog Cosmology And Superfluidity In Atomic Gases And Electronic Materials, Anshuman Bhardwaj

LSU Doctoral Dissertations

We present a study of analog cosmological models in Bose-Einstein condensates (BEC) and in graphene, and superfluidity in a box-shaped traps. We start by examining the dynamics of a Bose-Einstein condensate (BEC) trapped inside an expanding toroid that can realize an analog inflationary universe. The expanding condensate forces phonons to undergo redshift and damping due to quantum pressure, owing to the thinness of the ring. We predict that such expanding BECs can exhibit spontaneous phonon creation from the vacuum state and show how it would manifest in the atom density and density correlations and discuss connections with the inflationary theory. …

Stellar Binaries And Post-Merger Evolution: A Framework For Stellar Evolution And Nucleosynthesis In R Coronae Borealis Stars, Bradley Munson

LSU Doctoral Dissertations

We have developed a framework for simulating binary stars through all three relevant
timescales: the dynamical merger, thermal, and nuclear evolution. The framework begins by simulating a dynamical merger in a 3-dimensional hydrodynamics adaptive mesh refinement code, Octo-Tiger, and performing a spherical averaging calculation to map the post-merger remnant into the 1-dimensional stellar evolution code, MESA. In this work, we primarily utilize this framework for simulating double white dwarf mergers, which are believed to be the progenitor to R Coronae Borealis (RCB) stars. We evolve the post-merger in MESA and compare the computed surface abundances to those observed …

Measurement Of Near-Threshold Proton Branching Ratios In 31s Important For Novae, Sudarsan Balakrishnan

LSU Doctoral Dissertations

Classical novae are stellar explosions that contribute to the nucleosynthesis of isotopes on the proton-rich side of the valley of stability up to ⁴⁰Ca. In ONe novae, the incompletely understood reaction rate of ³⁰P(p,γ)³¹S is known to strongly influence the production rate of several stable isotopes such as ³⁰Si, ³¹P, and ^32,33,34S. A precise measurement of this reaction rate has several potential implications towards matching astrophysical observables to the physical composition of the nova site -- the observed elemental abundance ratios of O/S and S/Al have been suggested as useful `thermometers' to gauge …

Surpassing The Standard Quantum Limit Using An Optical Spring, Torrey Cullen

LSU Doctoral Dissertations

In 1916, Albert Einstein predicted the existence of gravitational waves based on his new theory of general relativity. He predicted an accelerating mass with a non-zero quadrupole moment would emit energy in the form of gravitational waves. Often referred to as ripples in space-time, gravitational waves are extremely small by the time reach Earth, potentially having traveled hundreds of megaparsecs. It is common for these ripples in space-time to stretch and squeeze matter 1000 times smaller than the width of a proton.
Laser interferometer observatories were first built in the 1990s in the US and Europe, and as sensitivity improvements …

From Equal-Mass To Extreme-Mass-Ratio Binary Inspirals: Simulation Tools For Next Generation Gravitational Wave Detectors, Samuel Douglas Cupp

LSU Doctoral Dissertations

Current numerical codes can successfully evolve similar-mass binary black holes systems, and these numerical waveforms contributed to the success of the LIGO Collaboration's detection of gravitational waves. LIGO requires high resolution numerical waveforms for detection and parameter estimation of the source. Great effort was expended over several decades to produce the numerical methods used today. However, future detectors will require further improvements to numerical techniques to take full advantage of their detection capabilities. For example, the Laser Interferometer Space Antenna (LISA) will require higher resolution simulations of similar-mass-ratio systems than LIGO. LISA will also be able to detect extreme-mass-ratio inspiral …

Ligers Interferometric Survey Of M Dwarf Diameters, Tyler Gregory Ellis

LSU Doctoral Dissertations

In this dissertation, I present the largest single collection of M dwarf stellar radii in over a decade and contextualize these measurements with the systematic model discrepancies. The measurements of stellar angular diameters are also important in the quantification of the properties of exoplanets. In order to estimate the property of the exoplanet, it is first necessary to quantify the properties of the planet's host star. Using the survey results complemented with previous direct observations of the angular diameters of low mass stars, I develop updated updated surface brightness relationships. These relationships allow predictions of angular diameters using easy to …

Reinforcement Learning In A Quantum Network, Roy Pace

Honors Capstones

No abstract provided.

Observing And Exploring Intrinsic Characteristics Of Type Ia Supernova, Connor Langevin

Honors Capstones

No abstract provided.

Are Long-Period Exoplants Around Cool Stars More Common Than We Thought?, Emily Jane Safron

LSU Doctoral Dissertations

The Kepler mission has been the catalyst for discovery of nearly 5,000 confirmed and candidate exoplanets. The majority of these candidates orbit Sun-like stars, and have orbital periods comparable to or shorter than that of the Earth, due to the selection bias inherent in the transit method and the limitations of automated transit search algorithms. We aim to develop a richer understanding of the population of exoplanets around the lowest-mass stars, the M spectral type. We are particularly interested in exoplanets with long orbital periods, which are difficult or impossible to find using standard transit search algorithms. In our study, …

The Spectra Of Hydrogen-Deficient Carbon Stars: The Effects Of Evolution And Nucleosynthesis, Courtney Lauren Crawford

LSU Doctoral Dissertations

The rare class of stars known as the Hydrogen-deficient Carbon (HdC) stars includes the R Coronae Borealis (RCB) variables and the non-variable Dustless HdC (dLHdC) stars. These stars are believed to be formed via the merger of two white dwarf (WD) stars. They are known to exhibit many spectral peculiarities, such as partial helium burning products, enhancement of s-processed material and severe hydrogen-deficiency. In this work I explore many facets of HdC evolution. I begin by creating 18 HdC models in the stellar evolution code Modules for Experiments in Stellar Astrophysics (MESA) by merging two WD progenitors and evolving the …

Gaia Gral: Gaia Dr2 Gravitational Lens Systems. Vii. Xmm-Newton Observations Of Lensed Quasars, Thomas Connor, Daniel Stern, Alberto Krone-Martins, S. G. Djorgovski, Matthew J. Graham

Faculty Publications

We present XMM-Newton X-ray observations of nine confirmed lensed quasars at 1 less than or similar to z less than or similar to 3 identified by the Gaia Gravitational Lens program. Eight systems are strongly detected, with 0.3-8.0 keV fluxes F (0.3-8.0) greater than or similar to 5 x10(-14) erg cm(-2) s(-1). Modeling the X-ray spectra with an absorbed power law, we derive power-law photon indices and 2-10 keV luminosities for the eight detected quasars. In addition to presenting sample properties for larger quasar population studies and for use in planning for future caustic-crossing events, we also identify three quasars …

A Multiparameter Degeneracy In Microlensing Events With Extreme Finite Source Effects, Samson A. Johnson, Matthew T. Penny, B. Scott Gaudi

Faculty Publications

For microlenses with sufficiently low mass, the angular radius of the source star can be much larger than the angular Einstein ring radius of the lens. For such extreme finite source effect (EFSE) events, finite source effects dominate throughout the duration of the event. Here, we demonstrate and explore a continuous degeneracy between multiple parameters of such EFSE events. The first component in the degeneracy arises from the fact that the directly observable peak change of the flux depends on both the ratio of the angular source radius to the angular Einstein ring radius and the fraction of the baseline …

Search Full Text Options Here 2 Of 4 Kmt-2021-Blg-0912lb: A Microlensing Super Earth Around A K-Type Star, Cheongho Han, Ian A. Bond, Jennifer C. Yee, Weicheng Zang, Michael D. Albrow

Faculty Publications

Aims. The light curve of the microlensing event KMT-2021-BLG-0912 exhibits a very short anomaly relative to a single-lens single-source form. We investigate the light curve for the purpose of identifying the origin of the anomaly.

Methods. We model the light curve under various interpretations. From this, we find four solutions, in which three solutions are found under the assumption that the lens is composed of two masses (2L1S models), and the other solution is found under the assumption that the source is comprised of binary stars (1L2S model). The 1L2S model is ruled out based on the contradiction that the …

Search For Continuous Gravitational Waves From 20 Accreting Millisecond X-Ray Pulsars In O3 Ligo Data, R. Abbott, T. D. Abbott, F. Acernese, K. Ackley, C. Adams

Faculty Publications

Results are presented of searches for continuous gravitational waves from 20 accreting millisecond x-ray pulsars with accurately measured spin frequencies and orbital parameters, using data from the third observing run of the Advanced LIGO and Advanced Virgo detectors. The search algorithm uses a hidden Markov model, where the transition probabilities allow the frequency to wander according to an unbiased random walk, while the J-statistic maximum-likelihood matched filter tracks the binary orbital phase. Three narrow subbands are searched for each target, centered on harmonics of the measured spin frequency. The search yields 16 candidates, consistent with a false alarm probability of …

Towards A Quantum Notion Of Covariance In Spherically Symmetric Loop Quantum Gravity, Rodolfo Gambini, Javier Olmedo, Jorge Pullin

Faculty Publications

The covariance of loop quantum gravity studies of spherically symmetric space-times has recently been questioned. This is a reasonable worry, given that they are formulated in terms of slicing-dependent variables. We show explicitly that the resulting space-times, obtained from Dirac observables of the quantum theory, are covariant in the usual sense of the way-they preserve the quantum line element-for any gauge that is stationary (in the exterior, if there is a horizon). The construction depends crucially on the details of the Abelianized quantization considered, the satisfaction of the quantum constraints, and the recovery of standard general relativity in the classical …

Towards A Quantum Notion Of Covariance In Spherically Symmetric Loop Quantum Gravity, Rodolfo Gambini, Javier Olmedo, Jorge Pullin

Faculty Publications

The covariance of loop quantum gravity studies of spherically symmetric space-times has recently been questioned. This is a reasonable worry, given that they are formulated in terms of slicing-dependent variables. We show explicitly that the resulting space-times, obtained from Dirac observables of the quantum theory, are covariant in the usual sense of the way-they preserve the quantum line element-for any gauge that is stationary (in the exterior, if there is a horizon). The construction depends crucially on the details of the Abelianized quantization considered, the satisfaction of the quantum constraints, and the recovery of standard general relativity in the classical …

Testing Effects Of Lorentz Invariance Violation In The Propagation Of Astroparticles With The Pierre Auger Observatory, P. Abreu, M. Aglietta, J. M. Albury, I. Allekotte, K. Almeida Cheminant

Faculty Publications

Lorentz invariance violation (LIV) is often described by dispersion relations of the form E-i(2) = m(i)(2) + p(i)(2) + delta E-i,n(2+ n) with delta different based on particle type i, with energy E, momentum p and rest mass m. Kinematics and energy thresholds of interactions are modified once the LIV terms become comparable to the squared masses of the particles involved. Thus, the strongest constraints on the LIV coefficients delta(i,n) tend to come from the highest energies. At sufficiently high energies, photons produced by cosmic ray interactions as they propagate through the Universe could be subluminal and unattenuated over cosmological …

A Gravitational-Wave Measurement Of The Hubble Constant Following The Second Observing Run Of Advanced Ligo And Virgo (Vol 908, 218, 2021), B. P. Abbott, R. Abbott, T. D. Abbott

Faculty Publications

No abstract provided.

Multi-Scale Feedback And Feeding In The Closest Radio Galaxy Centaurus A, B. Mckinley, S. J. Tingay, M. Gaspari, R. P. Kraft, C. Matherne, A. R. Offringa, M. Mcdonald, M. S. Calzadilla, S Veilleux, S. S. Shabala, S. D. J. Gwyn, J. Bland-Hawthorn, D. Crnojevic, B. M. Gaensler, M. Johnston-Hollitt

Faculty Publications

Supermassive black holes and supernova explosions at the centres of active galaxies power cycles of outflowing and inflowing gas that affect galactic evolution and the overall structure of the Universe(1,2). While simulations and observations show that this must be the case, the range of physical scales (over ten orders of magnitude) and paucity of available tracers make both the simulation and observation of these effects difficult(3,4). By serendipity, there lies an active galaxy, Centaurus A (NGC 5128)(5,6), at such a close proximity as to allow its observation over this entire range of scales and across the entire electromagnetic spectrum. In …