Stars, Interstellar Medium and the Galaxy Commons^™

The Aurora Survey: Robust Helium Abundances At High Redshift Reveal A Subpopulation Of Helium-Enhanced Galaxies In The Early Universe, Danielle A. Berg, Ryan L. Sanders, Alice E. Shapley, Michael W. Topping, Naveen A. Reddy, Evan D. Skillman, Erik Aver, Fergus Cullen, Callum T. Donnan, James S. Dunlop, Tucker Jones, Ali Ahmad Khostovan, Derek J. Mcleod, Desika Narayanan, Pascal A. Oesch, Anthony J. Pahl, Max Pettini, N. M. Förster Schreiber, Daniel P. Stark

Physics Faculty Scholarship

We present the first robust helium (He) abundance measurements in star-forming galaxies at redshifts 1.6 ≲ z ≲ 3.3 using deep, moderate-resolution JWST/NIRSpec spectroscopy from the AURORA survey. We establish a high-z He sample consisting of 20 galaxies with multiple high-signal-to-noise-ratio (>5σ) He i emission-line detections, including the critical near-infrared λ10833 line. This is the first study at high redshift leveraging λ10833 to break degeneracies between temperature, electron density, optical depth, and He+/H+, enabling reliable He abundance determinations in the early Universe. We use a custom Markov Chain Monte Carlo framework incorporating direct-method electron …

Stars And Shapes: An Investigation Of Stripped Envelope Supernovae Structures Using Spectropolarimetry Observations And Hydrodynamic Models, Sabrina Desoto

Electronic Theses and Dissertations

Supernovae (SNe) are the energetic deaths of massive stars, dispersing heavy elements throughout the galaxies and shaping cosmic evolution across the universe. However, understanding the connections between the evolution of massive stars, their catastrophic demises, and the myriad of observed SNe, remains a fundamental challenge in astrophysics. My work aims to narrow this gap by integrating extensive observational data with advanced hydrodynamical simulations to better interpret SNe observations and understand the origin of their geometry. The observational component utilizes the largest spectropolarimetry dataset of stripped-envelope (SE) core-collapse supernovae (CCSNe) gathered by the SNSPOL project. Analyzing nine Type Ib and eleven …

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 …

Numerical Simulations Of Highly Eccentric Systems Of Binary Neutron Stars With Spin, Victoria White

Harriet L Wilkes Honors College Theses

Binary Neutron Star (BNS) mergers are among the most energetic events in the universe, producing gravitational waves, electromagnetic radiation, and heavy elements. While previous research has utilized simulations for collisions, few studies have accounted for how the spin of the stars affects mergers. This thesis contains a general overview of the topic and a research component conducted in the field of numerical relativity. High-performance computing was used to simulate BNS collisions, examining how spin affects the inspiral, merger, and post-merger phases. Computations used the Einstein Toolkit, Cactus framework, and the numerical tool developed by the FAU Relativity Group, Sgrid. The …

X-Ray Microcalorimeter Observations Of High-Mass X-Ray Binaries With The Resolve Instrument Onboard Xrism, Pragati Pradhan, Masahiro Tsujimoto

Publications

The X-ray Imaging and Spectrometer Mission (XRISM) was put into orbit successfully in September 2023. Resolve, one of the scientific instruments onboard XRISM, hosts an X-ray spectrometer based on X-ray microcalorimetery technology. It excels in high spectral resolution, a large throughput, a large bandpass, low background, and good timing accuracy. These properties are suited to bring new insights especially in high-mass X-ray binaries (HMXB). We describe these unique features of Resolve and present initial highlights of two HMXB sources.

The Giant Outburst Of Exo 2030+375, P. Thalhammer, R. Ballhausen, E. Sokolova-Lapa, J. Stierhof, A. Zainab, R. Staubert, K. Pottschmidt, J.B. Coley, R.E. Rothschild, G.K. Jaisawal, B. West, P.A. Becker, Pragati Pradhan, P. Kretschmar, J. Wilms

Publications

The Be X-ray binary EXO 2030+375 went through its third recorded giant outburst from June 2021 to early 2022. We present the results of both spectral and timing analysis based on NICER monitoring, covering the 2−10 keV flux range from 20 to 310 mCrab. Dense monitoring with observations carried out about every second day and a total exposure time of ∼160 ks allowed us to closely track the source evolution over the outburst. Changes in the spectral shape and pulse profiles showed a stable luminosity dependence during the rise and decline. The same type of dependence has been seen in …

The Unaltered Pulsar: Gro J1750-27, A Supercritical X-Ray Neutron Star That Does Not Blink An Eye, C. M. Malacaria, L. Moritz Ducci, M. Falanga, D. A. Altamirano, E. Bozzo, S. J. Guillot, G.K. Jaisawal, P. Kretschmar, M. Ng, Pragati Pradhan, R. Rothschild, A. Sanna, P. Thalhammer, J. Wilms

Publications

When accreting X-ray pulsars (XRPs) undergo bright X-ray outbursts, their luminosity-dependent spectral and timing features can be analyzed in detail. The XRP GRO J1750-27 recently underwent one such episode, during which it was observed with NuSTAR and monitored with NICER. Such a data set is rarely available, as it samples the outburst over more than 1 month at a luminosity that is always exceeding ∼5 × 1037 erg s−1 . This value is larger than the typical critical luminosity value, where a radiative shock is formed above the surface of the neutron star. Our data analysis of the joint spectra …

Determining The Light Curve And 3d Shape Of Asteroid Eunomia And Egeria Using Relative Photometry, Skylar G. Butler, Jackson Ladd Sackrider

Discovery Day - Daytona Beach

Asteroids are relics of our solar system’s early formation, preserving valuable information about planetary evolution. Understanding their rotational properties and surface features provides deeper insights into the dynamical and thermophysical processes that shape their evolution. This study aims to conduct photometric observations of two main-belt asteroids, Egeria and Eunomia, using the Embry-Riddle Aeronautical University 1-meter telescope. Observations will be conducted in the red band on February 28 and March 14, 2025, over five-hour sessions, capturing full rotational light curves for each asteroid. These data will be analyzed using MPO Canopus to generate 3D surface models through photometric inversion techniques. The …

Multi-Wavelength Study Of 1erass J085039.9−421151 With Erosita, Nustar, And X-Shooter, A. Zainab, A. Avakyan, V. Doroshenko, P. Thalhammer, E. Sokolova-Lapa, R. Ballhausen, N. Zalot, J. Stierhof, S. Hämmerich, C. M. Diez, P. Weber, T. Dauser, K. Berger, P. Kretschmar, K. Pottschmidt, Pragati Pradhan, N. Islam, C. Maitra, J.B. Coley, P. Blay, R.H.D. Corbet, R.E. Rothschild, K. Wood, A. Santangelo, U. Heber, J. Wilms

Publications

The eROSITA instrument on board Spectrum-Roentgen-Gamma (SRG) has completed four scans of the X-ray sky, leading to the detection of almost one million X-ray sources in eRASS1 alone, including multiple new X-ray binary candidates. We report on analysis of the X-ray binary 1eRASS J085039.9−421151, using a ∼55 ks long NuSTAR observation, following its detection in each eROSITA scan. An analysis of the eROSITA and NuSTAR X-ray spectra in combination with X-shooter data of the optical counterpart provide evidence of an X-ray binary with a red supergiant (RSG) companion, confirming previous results. However, we did determine a cooler spectral type for …

Stable Coronal X-Ray Emission Over 20 Yr Of Xz Tau, Steven M. Silverberg, Hans Moritz Günther, Pragati Pradhan, David A. Principe, P.C. Schneider, Scott J. Wolk

Publications

XZ Tau AB is a frequently observed binary young stellar object in the Taurus Molecular Cloud; XZ Tau B has been classified as an EXOr object. We present new Chandra/HETG-ACIS-S observations of XZ Tau AB, complemented with variability monitoring of the system with XMM-Newton, to constrain the variability of this system and identify high-resolution line diagnostics to better understand the underlying mechanisms that produce the X-rays. We observe two flares with XMM-Newton but find that outside of these flares the coronal X-ray spectrum of XZ Tau AB is consistent over 20 yr of observations. We compare the ensemble of XZ …

A Search For Subdwarf B Binaries Using Pulsation Timing From Tess, Tomomi Otani, Andrzej S. Baran, Lindsay C. Spence, Ted A. Von Hippel, Ellesse A. Lynum-Lozano, Julia M. Clark

Publications

Hot subdwarf B (sdB) stars are post-main-sequence stars of high temperature and gravity. Approximately 30% of sdBs exhibit stable pressure and/or gravity-mode pulsations, which can be used via the timing method to test for companion stars and determine their orbital solutions. We used short cadence data from the Transiting Exoplanet Survey Satellite (TESS) to search for previously undiscovered companions to sdBs. In this paper, we focus on searching for companions with orbital periods shorter than 13.5 days which are detectable within one sector of TESS data (about 27 days). The timing method requires that we derive pulsation frequencies in subsets …

The Density Distribution Of The Material Around Betelgeuse, Iman Behbehani

Dissertations, Theses, and Capstone Projects

Betelgeuse is a red supergiant star visible in the constellation Orion. Its windy and highly convective surface results in a complicated mass loss pattern difficult to understand and replicate in simulations. The ejected mass can form a shell around the star we consider the circumstellar material (CSM). In this study, we use ALMA interferometric observations to find the structure of Betelgeuse's CSM, and connect to the mass loss mechanisms that could form it. We measure a bipolar circumstellar structure with a position angle of 42.3$\pm 7.0^\circ$. We observe asymmetries in the form of hot spots in the north east of …

Leveraging Stellar Chemistry For A Global View Into The Atmospheres Of Brown Dwarfs And Giant Exoplanets, Emily Calamari

Dissertations, Theses, and Capstone Projects

In the era of the James Webb Space Telescope (JWST), it is now possible to examine substellar mass atmospheres in unparalleled detail and precision. However, unraveling the complicated thermodynamics and chemistry in these atmospheres remains a challenge. Atmospheric retrievals are a leading data-driven technique capable of recovering an object’s fundamental parameters such as mass, radius, effective temperature, gravity, cloud structure and composition and chemical abundances. However, in directly imaged or isolated worlds, constraining and/or interpreting these fundamental parameters can be difficult, particularly as retrieval models try to parameterize the overall impact of clouds.

For my dissertation, I turned to main …

How To Form A Gravitational-Wave Source: Quantifying Intermediate Evolutionary Stages In Isolated Binary Stellar Evolution, Ana Lam

Dissertations, Theses, and Capstone Projects

Gravitational-wave (GW) detections from double compact object (DCO) mergers provide crucial observational constraints for understanding massive stars across cosmic time. Coupled with these observations, binary population synthesis simulations become powerful tools for probing the formation, evolution, and ultimate fates of their progenitors---massive binary stars. However, complex evolutionary pathways, shaped by key intermediate stages such as mass transfer phases and supernovae, present a significant challenge to assess their impact. To address this, we develop a framework to quantify the influence of intermediate evolutionary stages on GW sources. By combining Sankey diagrams with survival factors, we systematically investigate how intermediate stages influence …

Refining Orbits And Revealing Origins: A Study Of Giant Exoplanets Around Low-Mass Stars, Angeli Sandoval

Dissertations, Theses, and Capstone Projects

The study of gas giants around low-mass stars offers important insight into planet formation. Core accretion models predict that these planets should have a low likelihood of forming due to the limited disk masses of their host low-mass stars. However, NASA space missions such as Kepler and TESS have revealed an emerging population of Saturn- and Jupiter-like planets around M-dwarfs (referred to as giant exoplanets orbiting M-dwarfs or GEMS) that challenge these expectations. This thesis investigates the detection, confirmation, and analysis of GEMS through pipeline development and a detailed analysis of two systems.

In Chapter 1, I provide background information …

Satellite-Host Galaxy Co-Evolution With Next-Generation Regulator Models, Austen Gabrielpillai

Dissertations, Theses, and Capstone Projects

The evolution of satellites galaxies is an unsolved problem in galaxy formation. Recent observations such as the SAGA and ELVES surveys find tension in HI contents and star formation of satellites around their central host galaxies when compared to our own local environment, the Milky Way. These processes are potentially highly influenced by the host's circumgalactic medium (CGM), and to constrain these cases requires accurate and fast modeling of satellites-host interactions. In this work, we present our methodology for evolving z = 0 surviving satellites alongside their central galaxy in sapphire, a CGM regulator co-evolution model of galaxy formation. …

Orbital Evolution Of The Datura Asteroid Family, Skylar G. Butler

Beyond: Undergraduate Research Journal

To research the Datura Family of asteroids, we used an orbital evolution code to track the orbital decay of asteroid fragments released in an asteroid disruption. Different particle sizes of 10, 100, 500, 750, and 100 micrometers were tracked including the semi-major axis, eccentricity, and inclination in order to observe how certain particle sizes’ orbital elements evolve. Using a young asteroid family like the Datura family gives more insight into the parent asteroid structure and formation because the time is closer to before the asteroid’s breakup. We use these models to constrain the parameters of the dust by comparing the …

Monte Carlo Stellar Evolution Models And Their Application On Globular Clusters, Jiaqi Ying

Dartmouth College Ph.D Dissertations

Stellar evolution models serve as fundamental tools in astronomy, essential for interpreting the interiors and evolutionary stages of stars, and have wide applications in astronomy, from searching for exoplanets to estimating the age of the universe. This thesis explores the inherent uncertainties arising from the complex physics used in stellar evolution models. By adopting a Monte Carlo approach to vary over 20 key stellar evolution parameters, we quantify their impact on model predictions, highlighting substantial influences on age, luminosity, and temperature. Through a detailed analysis of Milky Way globular clusters (GCs), this work rigorously investigates the uncertainties inherent in stellar …

Dust Observations Of Occulting Galaxy Pair Vv 191., Clayton Robertson

Electronic Theses and Dissertations

The presence of dust grains as part of the the interstellar medium (ISM) in galaxies is an all-impactful entity in astronomy due its influence on light, and therefore observations. Unlike a true blackbody, dust absorbs, reflects, reddens, and scatters light within a line of sight. We quantify this phenomena with attenuation: the difference between the observed and true magnitudes of an astronomical object due to dust. Therefore, to map dust attenuation, one needs a known background source of light. In the serendipitous case of partially overlapping –occulting– galaxies, the background galaxy serves as the known light source and the transmission …

Chemical & Electromagnetic Signatures Of Binary Neutron Star Mergers, Benjamin Amend

All Dissertations

Binary neutron star (BNS) mergers are some of the most energetic events in the universe, producing both short gamma-ray bursts (GRBs) and kilonovae. GRBs are brief, bright flashes of gamma rays, powered by ultra-relativistic jets launched during the merger. These jets produce a prompt burst of gamma rays, followed by a broadband afterglow generated by external shocks as the outflow interacts with the surrounding medium. Kilonovae are optical-infrared transients from the radioactive decay of heavy, neutron-rich nuclei formed through the rapid neutron capture process (r-process) in the merger ejecta. Together, GRBs and kilonovae provide unique laboratories for probing fundamental physics …

Using Moment Maps To Observe Hydrogen Gas In Markarian 54, Amaya Terry

Scholarly Horizons: University of Minnesota, Morris Undergraduate Journal

Hydrogen gas is useful when trying to understand galaxies because it helps make stars. In space, hydrogen gas is in many cases in a form called neutral hydrogen (HI). This gas emits a faint type of light called the 21 cm line, which is a type of radio wave. This light is useful because it can go through dust in space, unlike optical light. This means we can use it to look inside galaxies and study the gas even if there is dust that is in front of stars in the galaxy.

In my research I was given data from …

Examining Mulit-Wavelength Variability And Magnetic Interactions In The Polar St Lmi, Cain Rinkoski

Macalester Journal of Physics and Astronomy

Cataclysmic variable (CV) stars are interacting binary systems that exhibit exotic, multi-wavelength behavior driven by mass transfer from a donor star onto a white dwarf. As rich laboratories for accretion physics, binary dynamics, and the origins of Type Ia supernovae, CVs have been well studied in the X-ray, ultraviolet, optical, and infrared—but remain comparatively underexplored in the radio regime. This paper presents simultaneous, time-resolved optical and radio observations of the magnetic CV ST LMi, aimed at constraining its emission mechanisms and orbital modulation.
The optical light curves display brightness variations of approximately 1.31 ± 0.02 magnitudes on a period of …

Auroral Hemispheric Power Asymmetry During Geomagnetic Storms: A Multi-Database Investigation Using Ae And Supermag Indices, Melvin J. Reyes Lozada

Morehead State Theses and Dissertations

A thesis presented to the faculty of the College of Science and Engineering at Morehead State University in partial fulfillment of the requirements for the Degree Master of Science by Melvin J. Reyes Lozada on June 20, 2025.

Tidal Heating In Gas Giant Ice Moons, Sage Benz-Narveson

Senior Seminars and Capstones

This presentation is on the icy moons of Jupiter and Saturn, Europa and Enceladus. They are both known for being relatively large moons of gas giants made of a lot of water ice with silicate cores. Both are also suspected to harbor liquid oceans underneath their icy surfaces, sustained by salinity and tidal heating. Liquid water is of extreme interest to astrobiologists, which this paper will address, but it is primarily about tidal heating and its implications for the size of the subsurface oceans.

Simulations Of Magnetar Spin-Down Lifetimes Using Magnetic Braking Models, Sophie Wessel

Honors College Theses

The beginnings of magnetar lifetimes are not very well understood. It is important to improve our understanding of magnetar origins in order to investigate possible evolutionary connections to other classes of NS, such as X-ray dim isolated NSs (XDINSs). Here we follow in the steps of another paper1 in modeling the spin evolution of magnetars, utilizing two avenues of evolution: one involving exponential B-field decay, and the other involving suband super-exponential B-field decay. We replicate the results of the paper, utilizing Monte Carlo methods to generate and evolve synthetic populations of magnetars, which are then compared to the current known …

The Effect Of Nuclear Isomers On S-Process Nucleosynthesis, Jaad Tannous

All Dissertations

s-Process nucleosynthesis is a process in which stars produce elements of mass range A = 57 to 210. Since the days of B2FH, immense work has gone into quantifying and computing s-process yields and pathways. We expand upon said work along two fronts. The first front sets up the framework for proper treatment of nuclear isomers in network calculations. We apply the framework to study 85Kr, which is a pivotal isotope in the s-process chain that affects the abundance yields of Strontium and Rubidium isotopes. In particular, we are interested in the ratio of 88Sr/86Sr and 87Rb which are important …

Constraining Neutron Star Kicks Through Gravitational Wave Detection, James Phillips

Graduate Theses and Dissertations

Neutron stars have, on average, much higher proper motions than those of hot and bright O and B type main sequence stars. Thus, it is widely suspected that asymmetries in core-collapse supernovae provide a substantial kick to these compact objects at birth. Gen- eral Relativity predicts that such supernova asymmetries will generate bursts of gravitational radiation, though no such burst has been yet detected. Here we argue that the polarization amplitudes of those gravitational waves can be used to calculate the kicks imparted on that nascent neutron star. We begin by reviewing the evidence for natal kicks, then we describe …

Extraterrestrial - Why They're Almost Certainly Out There, Marcus Brown

2025 Student Academic Showcase

This was an essay I did for my English Composition II class. It’s evaluating an argument from a TED talk of my choice. The TED talk I chose for this writing project was "Extraterrestrial’s - Why They’re Almost Certainly Out There” by Chris Crowe talking about the many exoplanets out there in our universe and beyond. The presentation explains the different sizes, the atmosphere, and the number of exoplanets capable of hosting life. The statistics were used in this analysis like the amount of hydrogen dioxide on each exoplanet. I had to determine if Chris Crowe did a good job …

Contact Binary Stars: A Roadmap To Their Nature And Evolution, Larry A. Molnar

University Faculty Publications and Creative Works

Notre Dame Physics & Astronomy Dept. Seminar, March 18th, 2025 with students L. Carr, J. Darrow Former students: J. Lau, L. Henderson, A. Avery, G. M. Le, M. Blain

Rapid Mid-Infrared Spectral Timing With Jwst: Grs 1915+105 During An Mir-Bright And X-Ray-Obscured State, P. Gandhi, E.S. Borowski, J. Byrom, R.I. Hynes, T.J. Maccarone, A.W. Shaw, O.K. Adegoke, D. Altamirano, M.C. Baglio, Y. Bhargava, C.T. Britt, D.A.H. Buckley, D.J.K. Buisson, P. Casella, N. Castro Segura, P.A. Charles, J.M. Corral-Santana, V.S. Dhillon, R. Fender, A. Gurpide, C.O. Heinke, A.B. Igl, C. Knigge, S. Markoff, G. Mastroserio, M.L. Mccollough, M. Middleton, J.M. Miller, J.C.A. Miller-Jones, S.E. Motta, J.A. Paice, D.D. Pawar, R.M. Plotkin, P. Pradhan, M.E. Ressler, D.M. Russell, T.D. Russell, P. Santos-Sanz, T. Shahbaz, T. Shahbaz, G.R. Sivakoff, D. Steeghs, A.J. Tetarenko, J.A. Tomsick, F.M. Vincentelli, M. George, M. Gurwell, R. Rao

Publications

No abstract provided.