Physical Sciences and Mathematics Commons^™

The Geometry And Density Of B-Emission Star Disks From Statistical Analysis And Numerical Simulations, Isabelle H. Cyr

Electronic Thesis and Dissertation Repository

This thesis is divided into 3 investigations. First we present a novel method to estimate the opening angles of Be star disks from interferometric axis ratio measurements, using Bayesian statistics and Monte Carlo techniques. A large set of theoretical axis ratios generated from disk models were compared to observational samples to determine which distribution best reproduces the observations. We find that the observed axis ratio distributions in the K-, H-, and N-band can best be explained by the presence of thin disks while measurements over the H$\alpha$ line point toward slightly thicker disks. Second, using a smoothed particle hydrodynamics (SPH) …

The Circumstellar Environments Of B-Emission Stars By Optical Interferometry, Bethany Grzenia

Electronic Thesis and Dissertation Repository

A series of B-emission (Be) stars was observed interferometrically and numerically modelled to be consistent with the observations. Uniform geometrical disks were used to make first-order inferences about the configuration of the disk systems’ extended structures and their extent on the sky. Later, the Bedisk-Beray-2dDFTpipeline was used to make sophisticated non-local thermodynamic equilibrium (LTE) calculations of the conditions within the disks. In the first instance, sixteen stars were observed in the near-infrared (K-band, 2.2 micron) with the Palomar Testbed Interferometer (PTI). The Bedisk portion of the pipeline was used to model disk temperature and density structures for B0, B2, B5 …

Formation And Past Evolution Of The Meteoroid Complex Of Comet 96p/Machholz, Abedin Yusein Abedin

Electronic Thesis and Dissertation Repository

The past dynamical evolution of the meteoroid streams associated with comet 96P/Machholz is investigated. The goal is to obtain a coherent picture of the past capture of this large comet into a short period orbit, and its subsequent breakup hierarchy. In particular, the aim is to constrain the earliest epoch that this large first precursor started to supply meteoroids into the interplanetary space. The fragments and meteoroid streams of that past cometary decay constitute a wide multiplex of interplanetary bodies, knows as the 96P/Machholz complex. The largest presently surviving fragment is comet 96P/Machholz, followed by a large amount of debris …

Emplacement Of The Foy, Hess And Pele Offset Dykes At The Sudbury Impact Structure, Canada, Eric A. Pilles

Electronic Thesis and Dissertation Repository

The 1.85 Ga Sudbury impact structure is the remnant of what is generally considered to have been an ~150–200 km diameter impact basin in central Ontario, Canada. The so-called Offset Dykes are impact melt dykes that are found concentrically around – and extending radially outward from – the Sudbury Igneous Complex (SIC), a ~3 km thick differentiated impact melt sheet. The dykes are typically composed of two main phases of granodiorite: an inclusion- and sulfide-rich granodiorite in the centre of the dyke, and an inclusion- and sulfide-poor granodiorite along the margins of the dyke. This study uses a combination of …

Dicke’S Superradiance In Astrophysics, Fereshteh Rajabi

Electronic Thesis and Dissertation Repository

It is generally assumed that in the interstellar medium much of the emission emanating from atomic and molecular transitions within a radiating gas happen independently for each atom or molecule, but as was pointed out by R. H. Dicke in a seminal paper several decades ago this assumption does not apply in all conditions. As will be discussed in this thesis, and following Dicke’s original analysis, closely packed atoms/molecules can interact with their common electromagnetic field and radiate coherently through an effect he named superradiance. Superradiance is a cooperative quantum mechanical phenomenon characterized by high intensity, spatially compact, burst-like features …

The Spectral Variability Of Astronomical Pahs, Matthew Shannon

Electronic Thesis and Dissertation Repository

Polycyclic aromatic hydrocarbons (PAHs) are highly abundant molecules found throughout the universe. Illuminated by ultraviolet photons, they can emit up to 10% of the total power output of star-forming galaxies and are involved in many important physical and chemical processes (e.g., gas heating). They produce prominent emission bands between 3-20 μm which vary strongly in intensity and spectral profile. The origins of these variations are not fully understood, which limits the use of PAHs as (ubiquitous) diagnostic tracers of physical conditions. To characterize their variability, we studied the relative intensities and profiles of the 10-20 μm PAH bands in a …

Similarity, Adequacy, And Purpose: Understanding The Success Of Scientific Models, Melissa Jacquart

Electronic Thesis and Dissertation Repository

A central component to scientific practice is the construction and use of scientific models. Scientists believe that the success of a model justifies making claims that go beyond the model itself. However, philosophical analysis of models suggests that drawing inferences about the world from successful models is more complex. In this dissertation I develop a framework that can help disentangle the related strands of evaluation of model success, model extendibility, and the ability to draw ampliative inferences about the world from models.

I present and critically assess two leading accounts of model assessment, arguing that neither is sufficient to provide …

What Governs Star Formation In Galaxies? A Modern Statistical Approach, Sahar Rahmani

Electronic Thesis and Dissertation Repository

Understanding the process of star formation is one of the key steps in understanding the formation and evolution of galaxies. In this thesis, I address the empirical star formation laws, and study the properties of galaxies that can affect the star formation rate.

The Andromeda galaxy (M31) is the nearest large spiral galaxy, and Therefore, high resolution images of this galaxy are available. These images provide data from various regions with different physical properties. Star formation rate and gas mass surface densities of M31have been measured using three different methods, and have been used to compare different star formation laws …

Modeling The Mass Function Of Stellar Clusters Using The Modified Lognormal Power-Law Probability Distribution Function, Deepakshi Madaan

Electronic Thesis and Dissertation Repository

We use the Modified Lognormal Power-law (MLP) probability distribution function to model the behaviour of the mass function (MF) of young and populous stellar populations in different environments. We begin by modeling the MF of NGC1711, a simple stellar population (SSP) in the Large Magellanic Cloud as a pilot case. We then use model selection criterion to differentiate between candidate models. Using the MLP we find that the stellar catalogue of NGC1711 follows a pure power-law behaviour below the completeness limit with the slope α = 2.75 for dN/dlnm ∝ m^(−α+1) in the mass range 0.89 M⊙ to 7.75 M⊙. …

Aging Comets And Their Meteor Showers, Quanzhi Ye

Electronic Thesis and Dissertation Repository

Comets are thought to be responsible for the terrestrial accretion of water and organic materials. Comets evolve very quickly, and will generally deplete their volatiles in a few hundred revolutions. This process, or the aging of comets, is one of the most critical yet poorly understood problems in planetary astronomy. The goal of this thesis is to better understand this problem by examining different parts of the cometary aging spectrum of Jupiter-family comets (JFCs), a group of comets that dominates the cometary influx in the near-Earth space, using both telescopic and meteor observations. We examine two representative JFCs and the …

X-Ray Populations In The Local Group: Insights With Hubble & Chandra, Neven Vulic

Electronic Thesis and Dissertation Repository

X-ray observations provide a unique perspective on the most energetic processes in the Universe. In particular, Low-mass X-ray binaries (LMXBs) found in globular clusters have been shown to depend on the mass, radius, and metallicity of the cluster. This thesis focuses on the impact environmental parameters have on X-ray sources and the underlying physical explanations for them.

I studied the X-ray binary population in M31 using 1 Ms of Chandra ACIS data and 6-filter photometry from the Panchromatic Hubble Andromeda Treasury Survey. From a sample of 83 star clusters we found the brightest and most compact star clusters preferentially hosted …

Analytic Models Of Brown Dwarfs And The Substellar Mass Limit, Sree Ram Valluri, Shantanu Basu, Sayantan Auddy

Physics and Astronomy Publications

We present the analytic theory of brown dwarf evolution and the lower mass limit of the hydrogen burning main-sequence stars and introduce some modifications to the existing models. We give an exact expression for the pressure of an ideal nonrelativistic Fermi gas at a finite temperature, therefore allowing for nonzero values of the degeneracy parameter. We review the derivation of surface luminosity using an entropy matching condition and the first-order phase transition between the molecular hydrogen in the outer envelope and the partially ionized hydrogen in the inner region.We also discuss the results of modern simulations of the plasma phase …

The Inner Gaseous Disks Of Herbig Be Stars, Parshati Patel

Electronic Thesis and Dissertation Repository

Herbig Ae/Be stars are intermediate mass (~2 to 20M_sun) pre-main sequence stars that inherit a circumstellar disk of dust and gas from their formation phase. The region of this disk closest to the star is entirely gaseous because dust evaporates at the high temperatures there, and this gaseous region is currently poorly understood. Using non-LTE circumstellar disk codes to model the optical and near-infrared spectra of five, early-type (B0Ve to B2Ve) Herbig Be stars obtained with the Canada-France-Hawaii telescope ESPaDOnS instrument, the density structure of each inner gaseous disks was determined and estimates of the disk masses and …

Insights From Unsupervised Clustering And Composite Spectral Analysis Into The Physical Properties Driving Emission And Absorption In Quasar Uv/Optical Spectra, Aycha Tammour

Electronic Thesis and Dissertation Repository

Although quasar spectra appear remarkably similar, subtle systematic differences are well- known and are linked to the physical conditions in the emitting regions. This thesis char- acterizes the properties of quasar optical and UV spectral features and reveals some of their underlying physical causes by analyzing large spectroscopic datasets from the Sloan Digital Sky Survey.

We first examine the narrow-line region using four optical emission lines with a range of ionization potentials (IPs) using a sample of 16,027 quasars with redshift z ≤ 0.75. We bin the sample using the continuum luminosity and the Hβ width to constrain the accretion …

On R - W1 As A Diagnostic To Discover Obscured Active Galactic Nuclei In Wide-Area X-Ray Surveys, Stephanie M. Lamassa, Francesca Civano, Marcella Brusa, Daniel Stern, Eilat Glikman, Sarah Gallagher, C. Meg Urry, Sabrina Cales, Nico Cappelluti, Carolin Cardamone, Andrea Comastri, Duncan Farrah, Jenny E. Greene, S. Komossa, Andrea Merloni, Tony Mroczkowski, Priyamvada Natarajan, Gordon Richards, Mara Salvato, Kevin Schawinski, Ezequiel Treister

Physics and Astronomy Publications

Capitalizing on the all-sky coverage of WISE and the 35% and 50% sky coverage from Sloan Digital Sky Survey and Pan-STARRS, respectively, we explore the efficacy of mR (optical) - (mid-infrared), hereafter , as a color diagnostic to identify obscured supermassive black hole accretion in wide-area X-ray surveys. We use the ∼16.5 deg2 Stripe 82 X-ray survey data as a test bed to compare with R - K, an oft-used obscured active galactic nucleus (AGN) selection criterion, and examine where different classes of objects lie in this parameter space. Most stars follow a well-defined path in R - K versus …

Applying Hierarchical Clustering To Broad Absorption Line Profiles For Quasar Classification, Nathalie Chantal Marie Thibert

2016 Undergraduate Awards

The region immediately surrounding an actively accreting supermassive black hole at the centre of a massive galaxy, the accretion disk, produces an enormous amount of radiation resulting in a luminous, short-lived phenomenon called a quasar. About 20% of quasars show broad, blue-shifted absorption features in their UV spectra, indicative of an outflowing wind from the accretion disk. These winds can remove angular momentum from the accretion disk, thereby contributing to the growth of the central black hole. Understanding these winds will help us to better constrain the details of how black holes grow during the quasar phase. The structures of …