Stars, Interstellar Medium and the Galaxy Commons^™

Topological Changes In The Magnetic Field Of Lq Hya During An Activity Minimum, Jyri J. Lehtinen, Maarit J. Käpylä, Thomas Hackman, Oleg Kochukhov, Teemu Willamo, Stephen C. Marsden, Sandra V. Jeffers, Gregory W. Henry, Lauri Jetsu

Information Systems and Engineering Management Research Publications

Aims. Previous studies have related surface temperature maps, obtained with the Doppler imaging (DI) technique, of LQ Hya with long-term photometry. Here, we compare surface magnetic field maps, obtained with the Zeeman Doppler imaging (ZDI) technique, with contemporaneous photometry, with the aim of quantifying the star’s magnetic cycle characteristics.

Methods. We inverted Stokes IV spectropolarimetry, obtained with the HARPSpol and ESPaDOnS instruments, into magnetic field and surface brightness maps using a tomographic inversion code that models high signal-to-noise ratio mean line profiles produced by the least squares deconvolution (LSD) technique. The maps were compared against long-term ground-based photometry acquired with …

Using Nasa's Tess Mission To Search For Extremely Low Mass White Dwarf Stars, Corinna Peña

Undergraduate Honors Thesis Collection

Extremely low-mass white dwarf stars (ELM) are white dwarf stars with a mass lower than 0.45 solar masses that could not have evolved through normal processes within the lifetime of our universe. Therefore, these objects can only be created through a common envelope phase or a stable Roche lobe overflow while in a binary. These objects have periods between a few minutes to a few hours, so they are very short lived which makes them very rare. My goal for this project was to find these ELM stars by using NASA's Transiting Exoplanet Survey Satellite (TESS) data. I analyzed this …

Utilizing Post-Newtonian Expansion To Determine Parameters Of Compact Binary Black Hole Mergers, Jarrod E. Rudis

Honors College

The process of determining parameters of black hole mergers requires complicated formulae like the Einstein Field Equations (EFEs) that can only be solved numerically with the help of supercomputers. This paper sought to explore an alternative method to prediction of parameters through the use of 1st order Post-Newtonian Expansion (PNE), which is a way of approximating solutions to the EFEs. Two binary- black hole mergers, GW170814 and GW170809 were analyzed with the use of 1st order PNE to obtain the chirp mass and radiated energy parameters. These parameters were then compared with the parameters obtained using numerical solutions to the …

Monitoring The M-Dwarf Host Stars Of Tess Exoplanet Candidates: Stellar Flares And Habitability, Ashley Lieber

Physics Undergraduate Honors Theses

In the search for life beyond our solar system, the study of M-dwarfs has become increasingly important due to their unique characteristics including their small size, flaring capabilities, and long lifespans. Their small size allows for exoplanet detection due to observable gravitational interactions, and the stellar flares could potentially trigger prebiotic life on exoplanets in the system. Lastly, their long lifespans may provide the conditions necessary to foster prebiotic life and the development of more complex organisms over time. Flare rate is a critical factor in determining the habitability of the exoplanet due to its potential to damage or incubate …

A Monte Carlo Method For Evaluating Empirical Gyrochronology Models And Its Application To Wide Binary Benchmarks, Tomomi Otani, Ted Von Hippel, Derek Buzasi, Terry Oswalt, Alexander Stone-Martinez, Patrice Majewski

Publications

No abstract provided.

Emergent Spectra Of Young X-Ray Emitting Populations Across Environments, Alex Siebenmorgen

Physics Undergraduate Honors Theses

We construct reasonably accurate models of the X-Ray spectra of a multitude of sources in M51. We construct both average and individual models for the sources, which are split into 16 groups as the counts per source increases. Then, we create a plot to show how the model-predicted values of column density (nH) and photon index (gamma) change with luminosity. These models will be used to create an accurate X-Ray stellar energy distribution (SED) for M51, and to better understand how the SED changes with environmental factors like metallicity and star formation rate (SFR).

Exploring The Glow Of The Universe In Gamma-Rays And Hunting Distant Agn, Changam Meenakshi Rajagopal

All Dissertations

The entirety of the γ-ray radiation permeating our Universe is encoded in the extragalactic γ-ray background. This is a superposition of resolved sources, mostly powerful relativistic jets powered by supermassive black holes, i.e., blazars, and an unresolved isotropic component, aka, the diffuse isotropic gamma-ray background (IGRB). Studying the IGRB can help unveil its composition, as well as unearth multi-messenger relationships between the intensities of PeV neutrinos, ultra high energy cosmic rays (> 1018 eV), and sub-TeV γ-rays. The comparable energy budgets of these three phenomena (neutrinos, UHECR, and γ-rays) indicates a physical connection or a common source amongst them. On …

Improving White Dwarfs As Chronometers With Gaia Parallaxes And Spectroscopic Metallicities, Adam Moss, Ted Von Hippel, Elliot Robinson, Kareem El-Badry, David C. Stenning, David Van Dyk, Morgan Fouesneau, Coryn A.L. Bailer-Jones, Elizabeth Jeffery, Jimmy Sargent, Isabelle Kloc, Natalie Moticska

Publications

White dwarfs (WDs) offer unrealized potential in solving two problems in astrophysics: stellar age accuracy and precision. WD cooling ages can be inferred from surface temperatures and radii, which can be constrained with precision by high-quality photometry and parallaxes. Accurate and precise Gaia parallaxes along with photometric surveys provide information to derive cooling and total ages for vast numbers of WDs. Here we analyze 1372 WDs found in wide binaries with main-sequence (MS) companions and report on the cooling and total age precision attainable in these WD+MS systems. The total age of a WD can be further constrained if its …

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 …

Cepheid Variable Light Curve Analysis On The Embry-Riddle 1-Meter Telescope, Kayla Taylor

Beyond: Undergraduate Research Journal

This report details light curve analysis for four Cepheid variable stars (Polaris, RT Aurigae, RX Aurigae, and Zeta Geminorum) using Embry-Riddle Aeronautical University's 1-meter reflecting telescope and a SBIG-STX 16803 camera with a g filter. Observations were conducted once per week during the Spring 2021 semester; at least one three-hour shift was allotted per week according to the Observational Astronomy Telescope Allocation Committee (TAC). Individual light curves for each target Cepheid were then compared to published data to analyze evidence of evolution on the Instability Strip. Although the light curves showed the sinusoidal nature of brightness oscillations, amplitudes of the …

Nine Bright Γ Doradus Variables Discovered With Ground-Based Photometry, Gregory W. Henry, Francis C. Fekel, Michael H. Williamson

Information Systems and Engineering Management Research Publications

We have used precise photometric and high-dispersion spectroscopic observations to study nine candidate γ Doradus (γ Dor) stars, identified as optically variable comparison stars in our photometric studies of Sun-like stars. In this paper, we confirm these nine candidates as new γ Dor variables. All exhibit sinusoidal variability with amplitudes between 6 and 65 mmag in Johnson B and periods from 0.28 to 1.13 days. All lie in the same region of the H-R diagram as our previously confirmed γ Dor stars. Of the nine systems, one is a single-lined spectroscopic binary (SB1), two are double-lined spectroscopic binaries (SB2), and …

Erratum: Chandra Grating Spectroscopy Of Embedded Wind Shock X-Ray Emission From O Stars Shows Low Plasma Temperatures And Significant Wind Absorption, David H. Cohen, Winter Parts, Graham M. Doskoch, Jiaming Wang, Veronique Petit, Maurice A. Leutenegger, Marc Gagné

Earth & Space Sciences Faculty Publications

This is an erratum to the paper ‘ Chandra grating spectroscopy of embedded wind shock X-ray emission from O stars shows low plasma temperatures and significant wind absorption’ (2021, MNRAS, 503, 715). We present here a modest correction to the o v erall scaling of the differential emission measures (DEMs) of six O stars originally presented in Cohen et al. ( 2021 ). While working on a follow-up paper, we realized that we had incorrectly converted the bvapec spectral emission model’s normalization parameters (proportional to the emission measure per temperature bin size) to the emission measure per decade Kelvin shown …

The Dynamical Evolution Of Classical Be Stars, Keegan Marr

Electronic Thesis and Dissertation Repository

This thesis focuses on the evolution of the disks of two classical B-emission (Be) stars, 66 Ophiuchi and Pleione, and on the thermal structure for disks tilted out of the star's equatorial plane.

We used a hydrodynamic code to model the disk of the Be star 66 Ophiuchi. Observations from 1957 to 2020 were compiled to follow the growth and subsequent dissipation of the disk. Our models are constrained by new and archival photometry, spectroscopy and polarization observations. Using Markov chain Monte Carlo methods, we confirm that 66 Oph is a B2Ve star. We constrain the density profile of the …

Chandra Revisits Wr 48a: Testing Colliding Wind Models In Massive Binaries, Svetozar A. Zhekov, Marc Gagné, Stephen L. Skinner

Earth & Space Sciences Faculty Publications

We present results of new Chandra High-Energy Transmission Grating (HETG) observations (2019 November-December) of the massive Wolf-Rayet binary WR 48a. Analysis of these high-quality data showed that the spectral lines in this massive binary are broadened (full width at half-maximum, FWHM = 1400 km s(-1)) and marginally blueshifted (similar to-100 km s(-1)). A direct modelling of these high-resolution spectra in the framework of the standard colliding stellar wind (CSW) picture provided a very good correspondence between the shape of the theoretical and observed spectra. Also, the theoretical line profiles are in most cases an acceptable representation of the observed ones. …

Dr. Jennifer Hoffman, Anit Tyagi

DU Undergraduate Research Journal Archive

An interview with Dr. Jennifer Hoffman.

The Meaning Of Dark, Light And Shadows: Inferences In Art, Materiality And Cultural Practices, Frank Prendergast

Book/Book Chapter

Our visual awareness relies on light acting on the eye to perceive materiality and colour. Medieval thought wrestled to articulate and comprehend its nature. The notebooks of Leonardo Da Vinci, for example, included his descriptions to define light and make comparisons so as to differentiate between light and shadow. His focus was on the illumination of surfaces from the perspective of a painter, seeing shadows as ‘the diminution of light by the intervention of an opaque body’ and ‘the counterpart of luminous rays’. In his mind, a shadow ‘stood between light and darkness’, with darkness being ‘the absence of light’. …

First Steps In The Small-Scale Structure Formation In The Universe: The Emergence Of Galaxies, Da Bi

Theses and Dissertations--Physics and Astronomy

Galactic morphology in the contemporary universe results from the convergence of a long list of physical processes, not all of them yet fully understood and quantified. The universe exhibits a hierarchical structure: galaxies grow being immersed in dark matter (DM) halos, which in turn are fed by diffuse and filamentary accretion. I use a suite of very high-resolution zoom-in cosmological simulations of galaxies in order to study the assembly of galaxies at high redshifts, z ≥ 2, to quantify the role of environment and of the parent DM halos in this procss. My models have been chosen to lie within …

Stellar Parameter Determination For The Mastar Stellar Library, Daniel J. Lazarz

Theses and Dissertations--Physics and Astronomy

Empirical libraries of stellar spectra represent a key ingredient needed for modeling the integrated spectra of stellar populations, such as galaxies, through a process called stellar population synthesis (SPS). In order to make use of such libraries, accurate stellar atmospheric parameter estimates are required. Here, I present a methodology that was developed to build a stellar parameter catalog to accompany the MaNGA stellar library (MaStar), a comprehensive collection of empirical, medium-resolution stellar spectra. This parameter catalog was constructed using a multicomponent χ² fitting approach to match the MaStar spectra to models generated by interpolating the ATLAS9-based BOSZ models. The …

Milky Way Morphology Probed By 6d Astrometric Data From The Gaia Space Telescope, Joshua Taylor Harry

Theses and Dissertations--Physics and Astronomy

At varying height above and below the plane of the Milky Way, I have used astrometric methods to classify stars of different galactic components of the Milky Way - the thin disk, thick disk, and stellar halo. This work complements prior study of Milky Way sub-structure - notably involving number density and/or pairwise correlations - which demonstrate non-steady state effects in the galaxy, such as axial/north-south symmetry breaking or more complex phenomena like the Gaia snail. This has motivated my exploration of stellar population changes with height about the Milky Way mid-plane, and the study of symmetry in such changes …

Constraining The Star Formation Histories Of Galaxies In The Swift/Uvot + Manga (Swim) Value-Added Catalog, Nikhil Ajgaonkar

Theses and Dissertations--Physics and Astronomy

Although our understanding about galaxy evolution has improved in the past few
decades, we still do not understand how galaxies suddenly stop forming stars and move towards a quiescent phase. In order to do that, we must derive the Star Formation Histories (SFHs) of galaxies, that trace the change in Star Formation (SF) inside the galaxy over the cosmic timescale. This is achieved by using a set of spatially resolved near-ultraviolet (NUV) and optical spectroscopic images of the galaxies. We generate the Swift/UVOT + MaNGA value added catalog (SwiM VAC; Molina et al., 2020b) which comprises 150 galaxies having a …