Award Date

5-1-2012

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Physics and Astronomy

First Committee Member

Daniel Proga

Second Committee Member

Bing Zhang

Third Committee Member

Stephen Lepp

Fourth Committee Member

Balakrishnan Naduvalath

Number of Pages

124

Abstract

A simple 1D dynamical model of thermally driven disk winds is proposed, based on the results of recent, 2.5D axi-symmetric simulations. Our formulation of the disk wind problem is in the spirit of the original Parker (1958) and Bondi (1952) problems, namely we assume an elementary flow configuration consisting of an outflow following pre-defined trajectories in the presence of a central gravitating point mass. Viscosity and heat conduction are neglected. We consider two different streamline geometries, both comprised of straight lines in the (x,z)-plane: (i) streamlines that converge to a geometric point located at (x,z)=(0,-d) and (ii) streamlines that emerge at a constant inclination angle from the disk midplane (the x-axis, as we consider geometrically thin accretion discs). The former geometry is commonly used in kinematic models to compute synthetic spectra, while the latter, which exhibits self-similarity, is likely unused for this purpose, although it easily can be with existing kinematic models. We make the case that it should be, i.e. that geometry (ii) leads to transonic wind solutions with substantially different properties owing to its lack of streamline divergence. Pertinent to understanding our disk wind results, which are applicable to X-ray binaries, active galactic nuclei, and circumstellar discs, is a focused discussion on lesser known properties of Parker wind solutions. Parker winds are of wide applicability and have recently been used to predict photoevaporative mass loss rates from protoplanetary discs, but not without shortcomings, as we address. In addition, the analytical solutions of Parker winds are ideal for assessing and validating the accuracy of hydrodynamical simulations. Geometry (i) contains the spherically symmetric Parker wind solution as a special case, while one instance of geometry (ii) has been used as a testbed problem for hydrodynamic simulations performed in cylindrical coordinates. We present a parameter survey of our analytical solutions to facilitate their usage for numerical testing purposes, and show that, for a subset of the parameter space, Keplerian rotation allows for two transonic wind solutions for the same set of parameters.

Keywords

Disk Winds; Hydrodynamics; Mass Loss; Outflows; Protoplanetary Disks; Winds; Winds – Mathematical models

Disciplines

Astrophysics and Astronomy | Physics

Language

English


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