Thesis (Ph. D.)--University of Rochester. Dept. of Physics and Astronomy. / Vita. Facsim. photocopy. Ann Arbor, University Microfilms, 1973. Includes bibliographical references (leaves 78-81).

No description available.

Thesis (Ph.D.)--McMaster University, 2005. / Supervisor: Christine D. Wilson. Includes bibliographical references. Also available online.

Thesis (M.S.)--University of Toledo, 2009. / Typescript. "Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Master of Science in Physics." "A thesis entitled"--at head of title. Bibliography: leaves 70-71.

The properties of astrophysical masers are governed by the physical conditions of circumstellar envelopes of evolved stars, implying a connection between maser and mass-loss phenomena. Although similar studies to another type of mass-losing star, Asymptotic Giant Branch (AGB) stars, have been conducted, a quantitative understanding for the case of Red Supergiants (RSGs) is still largely lacking. Recently, more and more galactic massive clusters are discovered and studied, which provide a coeval environment to investigate the evolution of cool massive evolved stars with similar distance and metallicity. Among them, Westerlund 1 (Wd1) is one of the most massive open clusters, classified as Super Star Clusters (SSCs), within the Milky Way harboring 4 RSGs. We have 2 goals in this project. We aim to investigate the relationship between SiO maser detection and mass-loss behavior of RSGs in massive clusters, in order to explore the possibility of developing SiO maser as an evolutionary indicator of RSGs. We also aim to determine the kinematic properties of Wd1 with the aid of SiO maser. We report on observation of 43 GHz SiO (v = 1, J = 1–0) maser towards Wd1 conducted with Australia Telescope Compact Array (ATCA). We also make use of archival 22 GHz H2O maser (616–523) in help of studying kinematic of Wd1. We derive the maser detection information and stellar velocities from maser data. We also compile an extra sample of 36 RSGs, which surveyed in SiO maser before, within massive clusters, e.g. Red Supergiant Cluster 1 (RSGC1), Red Supergiant Cluster 2 (RSGC2), Perseus OB association 1 (Per OB 1) and Mercer et al.’s #8 (Mc8), and organize their photometric data from 2MASS, GLIMPSE, MSX, AKARI and WISE to derive their spectral energy distributions (SEDs). Luminosity, effective temperature and mass-loss rate are derived from fitting the SEDs with DUSTY model in order to search for correlations between mass-loss rate, SiO maser properties and evolution of RSGs. We detected SiO maser emission towards 2 RSGs (W 237 and W 26) in Wd1. These 2 RSGs also emit H2O maser as revealed from archival H2O maser observation data. We noticed that SiO masers tend to be detected towards RSGs with higher luminosity and mass-loss rate. We also determined the kinematic distance of Wd1 to be 3.3 kpc. From that result, we conclude that SiO maser is an effective evolution indicator for RSGs, which traces RSGs with high massloss rate. We also show that the age of RSGs in Wd1 is 10 ± 2 Myr which support the multi-generation star formation scenario in Wd1. / published_or_final_version / Physics / Master / Master of Philosophy

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Thesis (Ph. D.)--University of Wisconsin--Madison, 1983. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

No description available.

The aim of this thesis is to perform observational tests of SiO maser polarisation and excitation models, using component-level comparisons of multiple SiO maser transitions in the 43 GHz and 86 GHz bands at milliarcsecond resolution. These observations reqwre very long baseline interferometric imaging with very accurate polarimetric calibration. The supergiant star VY CMa was chosen as the object of this study due to its high SiO maser luminosity, many detected SiO maser lines, and intrinsic scientific interest. Two epochs of full-polarisation VLBA observations of VY CMa were performed. The Epoch 2 observations were reduced using several new data reduction methods developed as part of this work, and designed specifically to improve the accuracy of circular polarisation calibration of spectral-line VLBI observations at millimetre wavelengths. The accuracy is estimated to be better than 1% using these methods. The Epoch 2 images show a concentration of v= l and v=2 J= 1-0 SiO masers to the east and northeast of the assumed stellar position. The v=l J=2-1 masers were more evenly distributed around the star, with a notable lack of emission in the northeast. There is appreciable spatial overlap between these three lines. The nature of the overlap is generally consistent with the predictions of hydrodynamical circumstellar SiO maser simulations. Where the v=l J = 1-0 and J =2-1 features overlap, the v=l J = 2-1 emission is usually considerably weaker. This is not predicted by current hydrodynamical models, but can be explained in the context of collisional pumping in a low density environment. Six observational tests of weak-splitting maser polarisation models were performed, including intercomparisons of linear polarisation in the v=l J=1-0 and J=2-1lines, linear polarisation versus saturation level, linear polarisation versus distance from the star, circular polarisation in the v= l J = 1-0 and J=2-1 lines, circular versus linear polarisation and modeling of ~ 900 electric-vector position angle rotations. The polarisation model tests generally do not support non-Zeeman circular polarisation mechanisms. For the linear polarisation tests, the results are more consistent with models that predict similar linear polarisation across transitions. The scientific importance of these tests is described in detail and avenues for future work are described.