In my thesis I present a study of the dynamics and observational characteristics of massive circumstellar disks in two dimensions (r, φ) using two complimentary hydro-dynamic codes: a 'Smoothed Particle Hydrodynamic' (SPH) code and a 'Piecewise Parabolic Method' (PPM) code. I also study the detection limits available to radial velocity searches for low mass companions to main sequence stars. This thesis is organized as a series of published or submitted papers, connected by introductory and concluding material. I strongly recommend that readers of this abstract obtain the published versions of each of these papers. I first outline the progress which has been made in the modeling of the structure and origins of the solar system, then in chapter 2 (The Astrophysical Journal v502, p342, with W. Benz, F. Adams and D. Arnett), I proceed with numerical simulations of circumstellar disks using both hydrodynamic codes assuming a 'locally isothermal' equation of state. The disks studied range in mass from 0.05M* to 1.0 M* and in initial minimum Toomre Q value from 1.1 to 3.0. Massive disks (M(D) > 0.2 M*) tend to form grand design spiral structure with 1-3 arms, while low mass disks (M(D) ≤ 0.2M*) tend to form filamentary, > 4 armed spiral structures. In chapter 4 (submitted to The Astrophysical Journal with W. Benz and T. Ruzmaikina), I relax the assumption the locally isothermal evolution assumption and instead include simple heating and cooling prescriptions for the system. Under these physical conditions, the spiral arm growth is suppressed in the inner 1/3 of the disks relative to the isothermal evolution and in the remainder, changes character to more diffuse spiral structures. I synthesize spectral energy distributions (SEDs) from the simulations and compare them to fiducial SEDs derived from observed systems. The size distribution of grains in the inner disk can have marked consequences on the near infrared portion of the SED. After being vaporized in a hot midplane region, the grains do not reform quickly into the size distribution on which most opacity calculations are based. In chapter 6 (The Astrophysical Journal v500, p940 with Roger Angel), I examine the limits which may be placed upon the detection of planets, brown dwarfs and low mass stellar companions using radial velocity measurements. I derive an analytic expression describing the amplitude limits for periodic signals which may be obtained from a set of data of known duration, number of measurements and precision. In chapter 7, I outline several problems which may be profitably addressed by building on this work. (Abstract shortened by UMI.)
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/288969 |
| Date | January 1999 |
| Creators | Nelson, Andrew Frederick |
| Contributors | Benz, Willy |
| Publisher | The University of Arizona. |
| Source Sets | University of Arizona |
| Language | en_US |
| Detected Language | English |
| Type | text, Dissertation-Reproduction (electronic) |
| Rights | Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. |
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