Astrophysics and Astronomy Commons^™

Binary Neutron Star Mergers: Testing Ejecta Models For High Mass-Ratios, Allen Murray

The Journal of Purdue Undergraduate Research

Neutron stars are extremely dense stellar corpses which sometimes exist in orbiting pairs known as binary neutron star (BNS) systems. The mass ratio (q) of a BNS system is defined as the mass of the heavier neutron star divided by the mass of the lighter neutron star. Over time the neutron stars will inspiral toward one another and produce a merger event. Although rare, these events can be rich sources of observational data due to their many electromagnetic emissions as well as the gravitational waves they produce. The ability to extract physical information from such observations relies heavily on numerical …

Stability Of Regular Thin Shell Wormholes Supported By Vdw Quintessence, A. Eid

Applications and Applied Mathematics: An International Journal (AAM)

The dynamical equations of motion for a thin shell wormhole from regular black holes that are supported by Van der Waals (VDW) quintessence equation of state (EoS) are constructed, through cut and -paste technique. The linearized stability of regular wormhole is derived. The presences of unstable and stable static solutions with different value of some parameters are analyzed.

Band Extension And Possible Ridge Compression On Europa, Sarah Chinski

Macalester Journal of Physics and Astronomy

Jupiter's icy moon Europa has captivated and perplexed the scientific community since the discovery of its global liquid water ocean. Over the course of several missions to the Jovian system, high-resolution observations of Europa have determined that there are spreading zones where new crust is created, similar to the mid-ocean spreading tectonic process we observe on Earth. These features, known as bands, have symmetric hills and valleys, indicating brief events of activity where material from the interior is exuded through a central crack, and solidifies on both sides, creating two positive topography. Recently, Europan scientists have been questioning how these …

Discovering New Strong Gravitational Lenses In The Desi Legacy Imaging Surveys, Xiaosheng Huang, Christopher Storfer, A. Gu, V. Ravi, A. Pilon, W. Sheu, R. Venguswamy, S. Bankda, A. Dey, M. Landriau, D. Lang, A. Meisner, J. Moustakas, A. D. Myers, R. Sajith, E. F. Schlafly, D. J. Schlegel

Physics and Astronomy

We have conducted a search for new strong gravitational lensing systems in the Dark Energy Spectroscopic Instrument Legacy Imaging Surveys’ Data Release 8. We use deep residual neural networks, building on previous work presented in Huang et al. (2020). These surveys together cover approximately one third of the sky visible from the northern hemisphere, reaching a z-band AB magnitude of ∼ 22.5. We compile a training sample that consists of known lensing systems as well as non-lenses in the Legacy Surveys and the Dark Energy Survey. After applying our trained neural networks to the survey data, we visually inspect and …

A Numerical Approach To Modeling Submoons And Investigating Stability Regions, Josephine Spiegelberg

Honors Program Theses

The recent discovery of the Neptune-sized exomoon candidate Kepler-1625bi (Teachey et al. 2018) has prompted a wave of research into the possibility of such a large satellite hosting its own moons, or submoons. These submoons have a lot in common with moons, and lessons from moon stability calculations can help to understand submoon behavior and stability. Past submoon research has focused on determining stability regions for these submoons using simplified models of the body’s tidal evolution (Reid 1973, Conrad 1985, Kollmeier and Raymond 2019). In order to provide a more detailed understanding of submoon behavior, a Fortran N-Body code was …

Creating A Sample Of Off-Color Galaxies Using Big Data Tools, Christopher Becker

Honors Program Theses

This thesis begins an investigation into the presence of off-colored galaxies in the Sloan Digital Sky Survey. Through establishing the emergence and history of Astroinformatics, the thesis introduces the concepts surrounding both off-color galaxies and the Big Data tools helpful in analyzing the data to find them. A discussion of initial implementation methods and revised implementation due to difficulties with previous plans follows. Results are presented, with well in excess of 500,000 candidates for off-color galaxies present in the sample. Conclusions are then drawn regarding such a large sample and the implications this may have on the conventional understanding of …

Significance Of Gravitational Nonlinearities On The Dynamics Of Disk Galaxies, Alexandre Deur, Corey Sargent, Balša Terzić

Physics Faculty Publications

The discrepancy between the visible mass in galaxies or galaxy clusters and that inferred from their dynamics is well known. The prevailing solution to this problem is dark matter. Here we show that a different approach, one that conforms to both the current standard model of particle physics and general relativity (GR), explains the recently observed tight correlation between the galactic baryonic mass and the measured accelerations in the galaxy. Using direct calculations based on GR's Lagrangian and parameter-free galactic models, we show that the nonlinear effects of GR make baryonic matter alone sufficient to explain this observation. Our approach …

Preparing A Database Of Extremely High Velocity Outflows In Quasars, Griffin Kowash, Carla P. Quintero, Sean S. Haas, Paola Rodriguez Hidalgo

IdeaFest: Interdisciplinary Journal of Creative Works and Research from Cal Poly Humboldt

No abstract provided.

A Bayesian Approach To Deriving Ages Of Individual Field White Dwarfs, Erin M. O'Malley, Ted Von Hippel, David A. Van Dyk

Ted von Hippel

We apply a self-consistent and robust Bayesian statistical approach to determine the ages, distances, and zero-age main sequence (ZAMS) masses of 28 field DA white dwarfs (WDs) with ages of approximately 4-8 Gyr. Our technique requires only quality optical and near-infrared photometry to derive ages with <15% uncertainties, generally with little sensitivity to our choice of modern initial-final mass relation. We find that age, distance, and ZAMS mass are correlated in a manner that is too complex to be captured by traditional error propagation techniques. We further find that the posterior distributions of age are often asymmetric, indicating that the standard approach to deriving WD ages can yield misleading results.

The Disk Structure Of Late Type Galaxies: Determining The Black Hole Mass Function Of Low Surface Brightness Galaxies Through Logarithmic Spiral Arm Pitch Angle Measurement, Michael S. Fusco

Graduate Theses and Dissertations

This dissertation pertains to the geometric structure of late type (spiral) galaxies, specifically on the relation between the logarithmic spiral pitch angle of the galactic spiral arms with other properties of the galaxy, such as central Supermassive Black Hole (SMBH) mass. Our work continues a study of the Black Hole Mass Function (BHMF) in local galaxies by recording the pitch angles of spiral galaxies with lower surface brightness than were previously included. We also conduct a case study on the structure of an interestingly shaped galaxy, UGC 4599. Previous studies on the topic of spiral arm pitch angles have measured …

Thornado-Hydro: Generalizing Discontinuous Galerkin Methods For A Nuclear Equation Of State For Supernova Hydrodynamics, Brandon Lynn Barker, Eirik Endeve, Anthony Mezzacappa

Chancellor’s Honors Program Projects

No abstract provided.

Measuring Deterministic And Stochastic Gravitational Waves With Pulsar Timing Array Experiments, Kristina Islo

Theses and Dissertations

Pulsar timing arrays (PTAs) are uniquely poised to detect the nanohertz-frequency gravitational waves from supermassive black hole binaries (SMBHBs) formed during galaxy merger. Efforts are underway to observe three species of gravitational signal from these systems: the stochastic ensemble, individual, adiabatic binary inspirals, and bursts with memory. This dissertation discusses all three.

A typical Bayesian search for evidence of a stochastic gravitational wave background from the superposition of many unresolvable SMBHB inspirals requires weeks to months to deliver results. This is due in part to the inclusion of inter-pulsar spatial and temporal correlations induced in PTA data by such a …

Waveband Luminosity Correlations In Flux-Limited Multiwavelength Data, Jack Singal, V. Petrosian, Sami Malik, Jibran Haider

Physics Faculty Publications

We explore the general question of correlations among different waveband luminosities in a flux-limited multiband observational data set. Such correlations, often observed for astronomical sources, may be either intrinsic or induced by the redshift evolution of the luminosities and the data truncation due to the flux limits. We first address this question analytically. We then use simulated flux-limited data with three different known intrinsic luminosity correlations and prescribed luminosity functions and evolution similar to the ones expected for quasars. We explore how the intrinsic nature of luminosity correlations can be deduced, including exploring the efficacy of partial correlation analysis with …

Gwtc-1: A Gravitational-Wave Transient Catalog Of Compact Binary Mergers Observed By Ligo And Virgo During The First And Second Observing Runs, B. P. Abbott

Faculty & Staff Scholarship

We present the results from three gravitational-wave searches for coalescing compact binaries with component masses above 1 M⊙ during the first and second observing runs of the advanced gravitationalwave detector network. During the first observing run (O1), from September 12, 2015 to January 19, 2016, gravitational waves from three binary black hole mergers were detected. The second observing run (O2), which ran from November 30, 2016 to August 25, 2017, saw the first detection of gravitational waves from a binary neutron star inspiral, in addition to the observation of gravitational waves from a total of seven binary black hole mergers, …

The Invisible Sun: Building A Radio Interferometer Telescope, Isobel Curtin

Senior Projects Spring 2019

When we think of astronomy, we often associate the word implicitly with observing astronomical bodies with our own eyes, or from a signal collected in the visible light range. However, there is more information we can collect from these bodies when observing them using other kinds of light, unseen to the naked eye. Radio astronomy is an important tool in an astronomer’s toolkit, and can help us image hidden parts of the universe. Recently, radio astronomy was used to directly image a black hole in the center of a nearby galaxy for the first time!

This projects aims to further …

Database Review: Sao/Nasa Astrophysics Data System, Laura Pope Robbins

Publications

Laura Pope Robbins is an advisor for The Charleston Advisor, and the review below is included in Scholarly Commons with the permission of the publisher.

The Astrophysics Data System (ADS) is the premier Open Access research database for astronomy and astrophysics containing over 13 million bibliographic records. These records include journal articles, books, conference proceedings, historical observatory bulletins, and other gray literature. An exceptional feature of ADS is the visualizations it creates, showing author networks, overlapping citations, and frequently occurring terminology giving researchers new ways to explore the literature. It is a unique resource that is as easy for a …

Gamma-Ray Burst Classification: New Insights From Mining Pulse Data, Stanley Mcafee, Jon Hakkila

Journal of the South Carolina Academy of Science

Despite being the most energetic electromagnetic explosions in the universe, gamma-ray bursts (GRBs) are still poorly understood. The literature recognizes two potentially different types of GRB progenitors, although statistical data suggest the existence of three GRB classes. Reliable inference of GRB physics depends on the identification of appropriate classification attributes, as well as on the statistical classification techniques used. It has recently been shown that pulses are the basic unit of GRB emission. We use new data describing GRB pulse characteristics, in conjunction with data mining tools, to provide a more reliable gamma-ray burst classification system and place additional constraints …

Fermi-Bounce Cosmology And Scale-Invariant Power Spectrum, Stephon Alexander, Cosimo Bambi, Antonino Marcianò, Leonardo Modesto

Dartmouth Scholarship

We develop a non-singular bouncing cosmology using a non-trivial coupling of general relativity to fermionic fields. The usual Big Bang singularity is avoided thanks to a negative energy density contribution from the fermions. Our theory is ghost-free since the fermionic operator that generates the bounce is equivalent to torsion, which has no kinetic terms. The physical system consists of standard general relativity plus a topological sector for gravity, and fermionic matter described by Dirac fields with a non-minimal coupling. We show that a scale invariant power-spectrum generated in the contracting phase can be recovered by suitable choice s of fermion …

Using An Astrophysical Model To Characterize Nuclear Dust, Anita N. Dunsmore

Theses and Dissertations

Dust clouds resulting from nuclear explosions are complex phenomena, and knowledge on how they form is lacking. Noting the similarities between supernovae and nuclear explosions led to the concept of modeling a nuclear dust cloud using a supernova simulation. MOCASSIN uses a Monte Carlo approach to model photons traveling through a dust cloud, allowing the cloud's characteristics to be discovered by comparing an observed spectrum to a calculated one and then changing input values to make the spectra match. Data files describing two nuclear fireballs of varying yields were created and analyzed using MOCASSIN, but yielded zero energy spectra. After …

Cosmological Consequences Of Classical Flavor-Space Locked Gauge Field Radiation, Jannis Bielefeld, Robert R. Caldwell

Dartmouth Scholarship

We propose a classical SU(2) gauge field in a flavor-space locked configuration as a species of radiation in the early Universe, and show that it would have a significant imprint on a primordial stochastic gravitational wave spectrum. In the flavor-space locked configuration, the electric and magnetic fields of each flavor are parallel and mutually orthogonal to other flavors, with isotropic and homogeneous stress energy. Due to the non-Abelian coupling, the gauge field breaks the symmetry between left- and right-circularly polarized gravitational waves. This broken chiral symmetry results in a unique signal: nonzero cross-correlation of the cosmic microwave background temperature and …

Transfer Entropy And Cumulant Based Cost As Measures Of Nonlinear Causal Relationships In Space Plasmas: Applications To D St., Jay R. Johnson, Simon Wing, Enrico Camporeale

Faculty Publications

It is well known that the magnetospheric response to the solar wind is nonlinear. Information theoretical tools such as mutual information, transfer entropy, and cumulant based analysis are able to characterize the nonlinearities in the system. Using cumulant based cost, we show that nonlinear significance of D st peaks at 3–12 hours lags that can be attributed to VBs which also exhibit similar behavior. However, the nonlinear significance that peaks at lags 25, 50, and 90 hours can be attributed to internal dynamics, which may be related to the relaxation of the ring current. These peaks are absent in the …

A Microlensing Detection Algorithm For Wide-Field Surveys, Daniel Godines Alcantara

Senior Projects Spring 2018

Gravitational microlensing is a rare event in which the light from a foreground star (source star) is amplified temporarily as it goes around the Einstein radius of another star (lens star). This only occurs when the two stars align with the line of sight of the observer. The significance of microlensing is that it allows for the detection of planets, as when a planet orbiting the lensing star aligns within the Einstein radius, it acts as an additional lens that further amplifies the light. This results in a gaussian-like light curve with an additional deviation on the curve. Unlike transit …

Gw170817: Observation Of Gravitational Waves From A Binary Neutron Star Inspiral, B. P. Abbott, K. Aultoneal, S. Gaudio, K. Gill, E. M. Gretarsson, B. Hughey, M. Muratore, J. W. W. Pratt, S. G. Schwalbe, K. Staats, M. J. Szczepańczyk, M. Zanolin, Et Al.

Publications

On August 17, 2017 at 12∶41:04 UTC the Advanced LIGO and Advanced Virgo gravitational-wave detectors made their first observation of a binary neutron star inspiral. The signal, GW170817, was detected with a combined signal-to-noise ratio of 32.4 and a false-alarm-rate estimate of less than one per 8.0 × 104 years. We infer the component masses of the binary to be between 0.86 and 2.26 M⊙, in agreement with masses of known neutron stars. Restricting the component spins to the range inferred in binary neutron stars, we find the component masses to be in the range 1.17–1.60 M⊙, with the total …

Investigating Brown Dwarf Atmospheres: Gravity, Dust Content, Cloud Structure And Metallicity, Kendra Kellogg

Electronic Thesis and Dissertation Repository

Brown dwarfs are the lowest mass products of star formation. Their low masses don't allow them to sustain, or sometimes even begin, the thermonuclear processes that provide stars with internal energy and the thermal pressure necessary to maintain hydrostatic equilibrium. Thus, their radii and effective temperatures decrease as they age, continually changing their spectral classification. However, it is now a well-known fact that the spectral appearance of ultra-cool dwarfs is governed by more than just temperature. Factors such as gravity, metallicity and cloud distribution play an important role in the structure and composition of ultra-cool dwarf atmospheres and ultimately their …

Absolute Ages And Distances Of 22 Gcs Using Monte Carlo Main-Sequence Fitting, Erin M. O'Malley, Christina Gilligan, Brian Chaboyer

Dartmouth Scholarship

The recent Gaia Data Release 1 of stellar parallaxes provides ample opportunity to find metal-poor main-sequence stars with precise parallaxes. We select 21 such stars with parallax uncertainties better than σ _π /π ≤ 0.10 and accurate abundance determinations suitable for testing metal-poor stellar evolution models and determining the distance to Galactic globular clusters (GCs). A Monte Carlo analysis was used, taking into account uncertainties in the model construction parameters, to generate stellar models and isochrones to fit to the calibration stars. The isochrones that fit the calibration stars best were then used to determine the distances and ages …

X-Ray And Optical Study Of The Gamma-Ray Source 3fgl J0838.8–2829: Identification Of A Candidate Millisecond Pulsar Binary And An Asynchronous Polar, Jules P. Halpern, Slavko Bogdanov, John R. Thorstensen

Dartmouth Scholarship

We observed the field of the Fermi source 3FGL J0838.8−2829 in optical and X-rays, initially motivated by the cataclysmic variable (CV) 1RXS J083842.1−282723 that lies within its error circle. Several X-ray sources first classified as CVs have turned out to be γ-ray emitting millisecond pulsars (MSPs). We find that 1RXS J083842.1−282723 is in fact an unusual CV, a stream-fed asynchronous polar in which accretion switches between magnetic poles (that are ≈120° apart) when the accretion rate is at minimum. High-amplitude X-ray modulation at periods of 94.8 ± 0.4 minutes and 14.7 ± 1.2 hr are seen. The former appears …

A Differential Abundance Analysis Of Very Metal-Poor Stars, Erin M. O'Malley, Andrew Mcwilliam, Brian Chaboyer, Ian Thompson

Dartmouth Scholarship

We have performed a differential line-by-line chemical abundance analysis, ultimately relative to the Sun, of nine very metal-poor main-sequence (MS) halo stars, near [Fe/H] = −2 dex. Our abundances range from dex with conservative uncertainties of 0.07 dex. We find an average [α/Fe] = 0.34 ± 0.09 dex, typical of the Milky Way. While our spectroscopic atmosphere parameters provide good agreement with Hubble Space Telescope parallaxes, there is significant disagreement with temperature and gravity parameters indicated by observed colors and theoretical isochrones. Although a systematic underestimate of the stellar temperature by a few hundred degrees could explain this …

The X-Ray And Mid-Infrared Luminosities In Luminous Type 1 Quasars, Chien-Ting J. Chen, Ryan C. Hickox, Andrew D. Goulding, Daniel Stern

Dartmouth Scholarship

Several recent studies have reported different intrinsic correlations between the AGN mid-IR luminosity (L_MIR) and the rest-frame 2-10 keV luminosity (L_X) for luminous quasars. To understand the origin of the difference in the observed L_X−L_MIR relations, we study a sample of 3,247 spectroscopically confirmed type 1 AGNs collected from Bo\"{o}tes, XMM-COSMOS, XMM-XXL-North, and the SDSS quasars in the Swift/XRT footprint spanning over four orders of magnitude in luminosity. We carefully examine how different observational constraints impact the observed L_X−L_MIR relations, including the inclusion of X-ray non-detected objects, possible X-ray absorption …

Testing Metal-Poor Stellar Models And Isochrones With Hst Parallaxes Of Metal-Poor Stars, B. Chaboyer, E. O'Malley, G. F. Benedict, G. A. Feiden

Dartmouth Scholarship

Hubble Space Telescope (HST) fine guidance sensor observations were used to obtain parallaxes of eight metal-poor ([Fe/H] < −1.4) stars. The parallaxes of these stars determined by the new Hipparcos reduction average 17% accuracy, in contrast to our new HST parallaxes, which average 1% accuracy and have errors on the individual parallaxes ranging from 85 to 144 μas. These parallax data were combined with HST Advanced Camera for Surveys photometry in the F606W and F814W filters to obtain the absolute magnitudes of the stars with an accuracy of 0.02–0.03 mag. Six of these stars are on the main sequence (MS) (with −2.7 < [Fe/H] < −1.8) and are suitable for testing metal-poor stellar evolution models and determining the distances to metal-poor globular clusters (GCs). Using the abundances obtained by O'Malley et al., we find that standard stellar models using the VandenBerg & Clem color transformation do a reasonable job of matching five of the MS stars, with HD 54639 ([Fe/H] = −2.5) being anomalous in its location in the color–magnitude diagram. Stellar models and isochrones were generated using a Monte Carlo analysis to take into account uncertainties in the models. Isochrones that fit the parallax stars were used to determine the distances and ages of nine GCs (with −2.4 ≤ [Fe/H] ≤ −1.9). Averaging together the age of all nine clusters led to an absolute age of the oldest, most metal-poor GCs of 12.7 ± 1.0 Gyr, where the quoted uncertainty takes into account the known uncertainties in the stellar models and isochrones, along with the uncertainty in the distance and reddening of the clusters.

Data Mining By Grid Computing In The Search For Extrasolar Planets, Oisin Creaner [Thesis]

Doctoral

A system is presented here to provide improved precision in ensemble differential photometry. This is achieved by using the power of grid computing to analyse astronomical catalogues. This produces new catalogues of optimised pointings for each star, which maximise the number and quality of reference stars available. Astronomical phenomena such as exoplanet transits and small-scale structure within quasars may be observed by means of millimagnitude photometric variability on the timescale of minutes to hours. Because of atmospheric distortion, ground-based observations of these phenomena require the use of differential photometry whereby the target is compared with one or more reference stars. …