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The book Astro4U: An Introduction to the Science of the Cosmos excites students about the grandeur of astronomy and how the universe functions. Filled with vibrant figures and informative tables that support the written text, the book has a fresh, casual, student-friendly tone that dramatically increases interest in the material while also making it more accessible.The book provides a college-level description of science, with astronomy serving as the vehicle of delivery for displaying the scientific model. The content follows a traditional progression, beginning with a study of the sky, followed by discussions of ancient and medieval astronomy, modern scientific practices, and key physical principles. Chapters move through the Solar System, stars, then galaxies, and finally the cosmos as a whole. The book presents astronomy as the story of light and gravity, crucial threads that run through the text. Chapters include Ponder Sections—in-depth, quantitative passages dealing with particular applications of interest such as “space junk”, the solar energy budget, and light travel time. Appendices provide information about physical constants, astronomical symbols, and multiple choice problem sets.Because students often express concern about the math content in astronomy classes, the book begins with a chapter entitled “Astro Maths” that reviews all the mathematical skills and concepts needed to complete the course. This up-front investment increases student confidence, eliminates one of the primary blocks students face, and improves chances for student achievement and success.Astro4U is written for general education survey courses in astronomy that are geared toward non-science majors. / https://dc.etsu.edu/etsu_books/1188/thumbnail.jpg

abstract: One of the most fundamental questions in astronomy is how the Universe evolved to become the highly structured system of stars and galaxies that we see today. The answer to this question can be largely uncovered in a relatively unexplored period in the history of the Universe known as the Epoch of Reionization (EoR), where radiation from the first generation of stars and galaxies ionized the neutral hydrogen gas in the intergalactic medium. The reionization process created "bubbles" of ionized regions around radiating sources that perturbed the matter density distribution and influenced the subsequent formation of stars and galaxies. Exactly how and when reionization occurred are currently up for debate. However, by studying this transformative period we hope to unravel the underlying astrophysics that governs the formation and evolution of the first stars and galaxies. The most promising method to study reionization is 21 cm tomography, which aims to map the 3D distribution of the neutral hydrogen gas using the 21 cm emission lines from the spin-flip transition of neutral hydrogen atoms. Several radio interferometers operating at frequencies below 200 MHz are conducting these experiments, but direct images of the observed fields are limited due to contamination from astrophysical foreground sources and other systematics, forcing current and upcoming analyses to be statistical. In this dissertation, I studied one-point statistics of the 21 cm brightness temperature intensity fluctuations, focusing on how measurements from observations would be biased by different contaminations and instrumental systematics and how to mitigate them. I develop simulation tools to generate realistic mock 21 cm observations of the Hydrogen Epoch of Reionization Array (HERA), a new interferometer being constructed in the Karoo desert in South Africa, and perform sensitivity analysis of the telescope to one-point statistics using the mock observations. I show that HERA will be able to measure 21 cm one-point statistics with sufficient sensitivity if foreground contaminations can be sufficiently mitigated. In the presence of foreground, I develop a rolling foreground avoidance filter technique and demonstrate that it can be used to obtain noise-limited measurements with HERA. To assess these techniques on real data, I obtain measurements from the legacy data from the first season observation of the Murchison Widefield Array (MWA) and perform additional high-precision radio interferometric simulations for comparison. Through these works, I have developed new statistical tools that are complementary to the power spectrum method that is currently the central focus of the majority of analyses. In addition to confirming power spectrum detections, one-point statistics offer additional information on the distribution of the 21 cm fluctuations, which is directly linked to the astrophysics of structure formation. / Dissertation/Thesis / Doctoral Dissertation Astrophysics 2019

There are over 300 exoplanets detected through radial velocity surveys and photometric studies showing a tremendous variety of masses, compositions and orbital parameters. Understanding the way these planets formed and evolved within the circumstellar disks they were initially embedded in is a crucial issue. In the first part of this thesis we study the physical interaction between a gaseous protoplanetary disk and an embedded planet using numerical simulations. In order to trust the results from simulations it is important to compare different methods. However, the standard test problems for hydrodynamic codes differ considerably from the case of a protoplanetary disk interacting with an embedded planet. We have carried out a code comparison in which the problem of a massive planet in a protoplanetary disk was studied with various numerical schemes. We compare the surface density, potential vorticity and azimuthally averaged density profiles at several times. There is overall good agreement between our codes for Neptune and Jupiter-sized planets. We performed simulations for each planet in an inviscid disk and including physical viscosity. The surface density profiles agree within about 5% for the grid-based schemes while the particle codes have less resolution in the low density regions and weaker spiral wakes. In Paper II, we study hydrodynamical instabilities in disks with planets. Vortices are generated close to the gap in our numerical models in agreement with the linear modal analysis. The vortices exert strong perturbations on the planet as they move along the gap and can change its migration rate. In addition, disk viscosity can be modified by the presence of vortices. The last part of this thesis studies the mass transfer in symbiotic binaries and close T Tauri binary systems. Our simulations of gravitationally focused wind accretion in binary systems show the formation of stream flows and enhanced accretion rates onto the compact component.

Thesis (Ph. D.)--University of Washington, 1989. / Vita. Includes bibliographical references (leaves [442]-477).

<p>We present a study of satellites in orbit around high-resolution, smoothed particle hydrodynamics (SPH) galaxies simulated in cosmological contexts. For t he galaxies of similar mass to the Milky Way, the luminosity function at redshift zero of the satellites is similar to the observed luminosity function of the system of satellites orbiting the Milky Way. Analysis of the satellites' mass functions reveals an order of magnit ude more dark sat ellites than luminous for each galaxy. There are even dark subhalos more massive than some of the luminous subhalos. What separates luminous and dark subhalos is not their mass at z = 0, but t he maximum mass a subhalo attained over t heir life. We study the effect of four mass-loss mechanisms on the subhalos: ultraviolet (UV) ionising radiation, tidal stripping, ram pressure stripping, and stellar feeclback, and compare the impact each have on the satellites. In the lowest mass subhalos, UV is responsible for most of the gas loss and ram pressure stripping removes the rest. More massive subhalos have deeper potential wells and retain more mass during reionisation. However , as satellites pass near the centre of their main halo , tidal forces cause mass loss from satellites of all masses. It is difficult to discriminate mass loss due to this stellar feedback from other mechanisms using our analysis. During the course of this analysis, we noticed that massive and highly luminous subhalos accrete gas in a region that extends beyond their origins and traces their orbit around the host halo. We also ran a second series of t ests by varying the baryonic physics for a smaller galaxy and found that stellar feedback and UV ionisation do have a profound effect of the subhalos.</p> / Master of Science (MS)

<p>In the past, optical measurements of single crystals have provided insights into phase transitions, the structure and symmetry of the superconducting gap and many other phenomena. Competing groups are perpetually trying to improve the accuracy of measurements to contribute to the understanding of the materials they study. Recent improvements at McMaster included the installation of a translating stage that allowed for submillimeter control of sample position, the measurement of several samples in one experiment, and measurements at temperatures of 10 - 300 K. The stage was attached to an external sample chamber on a spectrometer that can be used to measure frequencies from 20 to 38,000 cm^-1. The new sample stage was used in measurements of the reflectance spectra of a single crystal URu2Si2 sample. The reflectance measurements were used to calculate the absolute reflectance and optical conductivity.<br /><br />It was observed that for temperatures below 50 K at frequencies below 100 cm^-1 , the reflectance appeared to have a parabolic trend. A linear regression was used to fit the absolute reflectance measured by Dr. Angel (2010) in order to determine the numeric values of the parabolic model with the best fit data. The regression gave the optimized equation: P = 0.9872 - 8.0279E-6*ω² with a regression coefficient of 0.8417. This showed that over 84% of the variability in the data was accounted for by the model. This model was used to calculate the absolute reflectance from the thermal reflectance data at 3 K collected by Dr. Angel (2010) and was shown to have a standard deviation of ±0.011. The result was called the "refined" absolute reflectance, and the refining method was repeated on the thermal reflectance measurements conducted by Dr. Nagel's group.</p> / Master of Science (MS)