Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 153 for “"Physics, Astronomy and Astrophysics"”.
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Constraints on the surface composition of Trojan asteroidsfrom near infrared (0.8-4.0 μm) spectroscopy and spectral modeling
… of primitive objects provides clues to understanding the conditions under which the solar system formed. Characterization of the inner solar nebula progresses rapidly due to remote studies of asteroid and planetary surfaces as well as laboratory analyses of meteorites and lunar samples. Because …
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Seyfert and starburst activity in galaxies: Modeling and analysis
… infrared study of galaxies with Seyfert and starburst activity, to constrain the impact of these phenomena on the host galaxy evolution in a local galaxy sample. We developed new tools for stellar population analysis in the infrared, using stellar absorption features. These tools are …
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Submillimeter heterodyne spectroscopy of star forming regions
… spectrum is on the frontier of both scientific and technical research in astrophysics. Being a relatively young field, scientific advancement is driven by advancements in detector technology. In this thesis, I discuss the design, construction, testing and deployment of two sub-mm wave heterodyne …
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Interferometric Mapping of Magnetic Fields in Star -Forming Regions
… decreases toward the high intensity regions and toward the center of the core. These results suggest that the dust polarization efficiency decreases toward the regions with high density and/or high optical depth.
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The Nature and Origin of Large Scale Diffuse X -Ray Emission in the Large Magellanic Cloud
… pc to ≥1000 pc. Here we examine the nature and origin of the large scale diffuse X-ray emission from the LMC. We first examine the large scale spatial distribution and physical conditions of hot gas in the LMC. We find that although the large scale diffuse X-ray emission with the highest …
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Empirical Constraints on O(5+) Outflows and Velocity Distributions in a Solar-Minimum Coronal Streamer
As part of an effort to understand how the solar wind is energized, the so-determined electron density is used to interpret O VI lambda1032, 1037 A spectra taken with UVCS. The spectra are interpreted in terms of empirical constraints on the O5+ ion velocity distributions and outflow speeds. Four …
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Circumstellar Distribution of Dust Grains Around Proto -Planetary Nebulae: Observational Evidence for Axisymmetry and 2.5-D Radiative Transfer Model Calculations
… from imaging surveys of PPNs at the mid-infrared and optical. In these imaging surveys, a prevalent axisymmetry has been found to reveal the equatorially-enhanced (toroidal) structure of the PPN shells. Moreover, two morphological types (SOLE-toroidal and DUPLEX-core/elliptical PPNs) have been …
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Evolution of the Circumstellar Atomic and Molecular Envelopes Around Evolved Stars
… For the more evolved protoplanetary nebula (PPN) and planetary nebula (PN) phases, the CSE also chronicles its interaction with fast winds and photodissociating/photoionizing radiation. Most AGB stars lose mass in spherically symmetric outflows, whereas PNe are largely axisymmetric. To investigate …
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The Mt. Laguna Infrared Cluster Survey: A Search for Galaxy Clusters Beyond Z = 1
… distant galaxy clusters conducted in the JHK' bands on the 1-m telescope at Mt. Laguna Observatory. By smoothing images after subtraction of foreground objects, clusters were detected by the fluctuations they cause in the near-infrared background light. False detections were eliminated by the J …
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Measuring the Cosmological Constant Through the Lyman -Alpha Forest Using the Alcock -Paczynski Test
… the major components of the Universe---OB, O DM and OLambda. Among these, the cosmological constant OLambda, which associates with the vacuum energy of our universe, draws specific attentions for its importance in fundamental particle physics. The Lyalpha forest QSO spectra are observationally …
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Observations of Large Biologically Important Interstellar and Cometary Molecules
Finally, we discuss the observational results of an extensive survey for biologically interesting molecules toward Comet Hale-Bopp (1995 O1). To date, no large biomolecule has ever been reported toward a comet with an array. The importance of detecting large biomolecules in comets is that in doing …
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Fundamental Properties of Galaxy Clusters: A Prelude to Large Scale Sunyaev-Zel'dovich Effect/near-Ir Cluster Surveys
… between the total galaxy luminosity or number and the cluster binding mass. The origins of such correlations are discussed in terms of a variation of star formation efficiency with cluster mass, various dynamical processes that affect galaxy evolution, and the hierarchical formation of …
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Statistical Analysis of the Cosmic Microwave Background: Power Spectra and Foregrounds
… foreground contamination on CMB experiments and describe the principle foregrounds. I show that it is possible to include the foreground components in a self-consistent fashion within the statistical framework of MAGIC and give explicit examples of how this might be achieved. Foreground …
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An Analytic Model of Environmental Effects on Cosmic Structure Formation and an Application to Cosmic Accretion Shock
… case of cosmic accretion shocks. We investigate and quantify the effect of environmental factors on the statistical properties of these shocks. For this purpose, we explore two different models. The first ""control"" model uses a Press-Schechter mass function to describe the population of …
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Protostar Formation in Magnetic Clouds: The Phase Beyond Ion Detachment
"We follow the formation and evolution of a molecular cloud core from mean molecular cloud densities to a density enhancement of twelve orders of magnitude, by which stage the magnetic flux problem of star formation is expected to be resolved. We use the nonideal six-fluid MHD equations, which we …
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Magnetic Fields in Star Forming Regions: Interferometric Mapping and Modeling
We developed a code to model and observe the polarized dust emission from arbitrary magnetic field configurations in star forming regions. We found that the interferometric observation will strongly overestimate the fractional polarization under most cases; however, we found that the position angle …
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3 Mm Spectral Line Surveys of the High Mass Star Forming Regions Sagittarius B2(N -Lmh) and Orion -Kl
… of this dissertation describes the methods and techniques used to analyze the data. The third chapter gives the results of the analysis of the data from the Sgr B2(N-LMH) line survey, where most large, saturated molecular species were constrained to a very small region in the cloud, with the …
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On the Ionization and Chemical Evolution of the Intergalactic Medium
… (z ∼ 15) alone explains the metal abundance and distribution at later redshifts. This idea is expanded in Chapter (8), by including an additional feedback from Population It stars formed in dwarf galaxies at redshifts z ≲ 10. We conclude that, the PopIII metals alone are insufficient to …
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Probing and Raising the Lithium Problems With Hadronic Gamma Rays and Cosmic -Ray Nucleosynthesis
… Thus there is an intimate link between Li and gamma-rays produced in CR interactions. In this thesis we explore this link and use it as a new, model-independent way of testing the CR nucleosynthesis of Li. We apply this tool to test a, still hypothetical, cosmological CR population. …
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Star Formation in OB Associations and Clusters
… level by the initial mass function (IMF), and at macroscopic level by space, time, and intensity. To understand how star formation proceeds across a region, all four parameters need to be examined. We used the resolved massive stars and young stellar objects (YSOs) in N 44 to study star …
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