Physical Sciences and Mathematics Commons^™

Nitrogen Abundances In Early-Type Be Stars, Ahmed Ahmed

Electronic Thesis and Dissertation Repository

A sample of 26 Be stars from the Magnetism in Massive Stars (MiMeS) spectroscopic survey are analyzed for their photospheric nitrogen abundances in an effort to detect rotational mixing in the Be stars. Be stars are massive stars, between 3 and 20 times the mass of the Sun, that are surrounded by a thin, equatorial disk of gas that produces emission lines in their optical and near-infrared spectra. Be stars are the most rapidly-rotating stellar population on the main sequence, where stars produce energy by core hydrogen burning. New, non-LTE line transfer calculations are performed for the Nii ion, the …

Probabilistic Reasoning In Cosmology, Yann Benétreau-Dupin

Electronic Thesis and Dissertation Repository

Cosmology raises novel philosophical questions regarding the use of probabilities in inference. This work aims at identifying and assessing lines of arguments and problematic principles in probabilistic reasoning in cosmology.

The first, second, and third papers deal with the intersection of two distinct problems: accounting for selection effects, and representing ignorance or indifference in probabilistic inferences. These two problems meet in the cosmology literature when anthropic considerations are used to predict cosmological parameters by conditionalizing the distribution of, e.g., the cosmological constant on the number of observers it allows for. However, uniform probability distributions usually appealed to in such arguments …

Stellar Spectroscopy: New Methods And Insights, Sanaz S. Golriz

Electronic Thesis and Dissertation Repository

The study of the chemical evolution of stars is of crucial importance since they play a major role in the enrichment of the chemistry of the universe. Throughout their lifetime, stars undergo several processes that can alter their chemistry. Gradually, the nucleosynthesis products from the interior of the star are radiatively and convectively levitated and mixed with the upper layers of the atmosphere. In the later stages of their evolution, low to intermediate mass stars (0.8-8.0~M☉) eject a significant fraction of these nucleosynthesis products, resulting in a circumstellar envelope of gas and dust around the central star with a very …

Methods And Results Toward Measuring Magnetic Fields In Star-Forming Regions, Scott C. Jones

Electronic Thesis and Dissertation Repository

Star formation is a fundamental process in the evolution of the cosmos. Yet given the abundance of stellar constituents, it remains prescient as to why the number of stars is not correspondingly large. If we cannot satisfactorily explain how stars are formed, then many further avenues of research are hindered. This thesis makes claims about one of the foremost theories as to the relative lack of stars, interstellar magnetic fields. These fields have been observationally verified on multiple scales. I will use the most direct method to probe magnetic fields in known star-forming regions, polarization, at millimetre/submillimetre wavelengths. In particular …

Rationality Of The Spectral Action For Robertson-Walker Metrics And The Geometry Of The Determinant Line Bundle For The Noncommutative Two Torus, Asghar Ghorbanpour

Electronic Thesis and Dissertation Repository

In noncommutative geometry, the geometry of a space is given via a spectral triple $(\mathcal{A,H},D)$. Geometric information, in this approach, is encoded in the spectrum of $D$ and to extract them, one should study spectral functions such as the heat trace $\Tr (e^{-tD^2})$, the spectral zeta function $\Tr(|D|^{-s})$ and the spectral action functional, $\Tr f(D/\Lambda)$.

The main focus of this thesis is on the methods and tools that can be used to extract the spectral information. Applying the pseudodifferential calculus and the heat trace techniques, in addition to computing the newer terms, we prove the rationality of the spectral action …