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Full-Text Articles in Physical Sciences and Mathematics

The Hα Spectroscopy Of Classical B-Emission Stars, Jessie M. Silaj Dec 2014

The Hα Spectroscopy Of Classical B-Emission Stars, Jessie M. Silaj

Electronic Thesis and Dissertation Repository

Classical B-emission (Be) stars are rapidly-rotating, massive stars that possess a dense, equatorial, gaseous disk. The presence of a disk was first inferred from the Balmer series emission that these stars exhibit, and Hα emission lines remain both a hallmark observational feature and one of the key diagnostics in determining the physical conditions within the disk.

In the first chapter of this thesis, we investigate the possible role of line-driven winds in disk formation. To test if line-driven winds could supply enough material to account for the equatorial disk, we check for the presence of Hα emission in the models ...


Molecular Gas In The Circumstellar Environment Of Unusual Evolved Stars, Sarah E. Malek Aug 2013

Molecular Gas In The Circumstellar Environment Of Unusual Evolved Stars, Sarah E. Malek

Electronic Thesis and Dissertation Repository

As low- and intermediate mass stars (with masses up to 8-9 solar masses) age, they experience a series of evolutionary changes which culminate in the removal of nearly their entire envelope through extensive mass loss. The ejected material cools down, which allows for the formation of molecules and the nucleation of dust grains in the circumstellar environment (CSE) of the star. Much about the properties and composition of the gas and dust in these CSEs is not well understood.

Here, we study the rich CSEs of two unusual evolved stars by analyzing spectral observations in the infrared and using molecular ...


The Continuum Linear Polarization Signature Of Classical Be Stars, Robbie J. Halonen Aug 2013

The Continuum Linear Polarization Signature Of Classical Be Stars, Robbie J. Halonen

Electronic Thesis and Dissertation Repository

Classical Be stars are rapidly-rotating, massive stars that exhibit distinct observational characteristics due to the presence of enveloping, equatorial disks of gas. While diligent observation of these objects has established a reliable description of their geometric and kinematic properties, our understanding of classical Be stars remains distressingly limited on the dynamical front. Principally, we lack a satisfactory characterization of the physical process(es) through which the gaseous disks form and dissipate. In order to understand the mechanisms that govern the development of these enigmatic stars, we use computational codes to produce theoretical models of these objects and their environments. We ...


Hot Stars With Disks, Erika Dawn Grundstrom Aug 2007

Hot Stars With Disks, Erika Dawn Grundstrom

Physics and Astronomy Dissertations

The evolutionary paths of the massive O and B type stars are often defined by angular momentum transformations that involve circumstellar gas disks. This circumstellar gas is revealed in several kinds of observations, and here I describe a series of investigations of the hydrogen line emission from such disk using detailed studies of five massive binaries and a survey of 128 Be stars. By examining three sets of spectra of the active mass-transfer binary system RY Scuti, I determined masses of 7.1 +/- 1.2 M_sun for the bright supergiant and 30.0 +/- 2.1 M_sun for the massive companion ...