Award Date

5-2011

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Physics

Department

Physics and Astronomy

First Committee Member

Daniel Proga, Chair

Second Committee Member

Stephen Lepp

Third Committee Member

Michael Pravica

Graduate Faculty Representative

Rohan Dalpatadu

Number of Pages

78

Abstract

We study mass outflows from astrophysical objects. Using numerical hydrodynamical simulations, we investigate outflows from accretion disks and exoplanets. In the first part of this dissertation, we present the results of Zeus 2D hydrodynamical simulations of the disk photosphere irradiated by strong X–rays that are produced in the innermost part of the disk of an accreting black hole. As expected, the irradiation heats the photosphere and drives a thermal wind. To apply our results to the well– studied X–ray transient source GRO J1655–40, we utilized the observed mass of its black hole and the observed properties of its X–ray radiation for our simulations. To compare our results with observations, we also computed transmitted X–ray spectra based on the wind solution. Our main finding is that the density of the fast–moving part of the wind is more than one order of magnitude lower than that inferred from the observations. Consequently, the model fails to predict spectra with line absorptions as strong and as blueshifted as those observed. However, despite the thermal wind being weak and Compton thin, the ratio between the mass–loss rate and the mass accretion rate is about seven. This high ratio is insensitive to the accretion luminosity, in the limit of lower luminosities. Most of the mass is lost from the disk between 0.07 and 0.2 of the Compton radius. We discovered that beyond this range the wind solution is self-similar. In particular, soon after it leaves the disk, the wind flows at a constant angle with respect to the disk. Overall, the thermal winds generated in our comprehensive simulations do not match the wind spectra observed in GRO J1655–40. This supports the conclusion of Miller et al. and Kallman et al. that the wind in GRO J1655–40, and possibly other X–ray transients, may be driven by magnetic processes. This in turn implies that the disk wind carries even more material than our simulations predict, and, as such, has a very significant impact on the accretion disk structure and dynamics. Motivated by the recent renaissance after the Kepler mission discoveries of about 500 new extrasolar planets, in the second part we analyze problems of the extrasolar planet irradiated by a star interacting with the wind coming from a parent star. This is a full 3D modeling performed using Athena 3D. We use the general model of a spherical object with a cosine distribution of temperature on the irradiated side and constant temperature on the opposite side. The thermal wind arises from the planet and interacts with the wind emanating from the star. We made some simplifications; the Coriolis force is included. We placed constraints on the mass loss from the planet, wind velocities, and dependencies on various parameters, such as: distance from the star, strength of the stars, wind, etc. We created a general model for studying outflows from diverse group of objects of various geometries.

Keywords

Accretion disk; Black holes (Astronomy); Extrasolar planets; Mathematical physics; Numerical simulation; Physical modeling; Physicsysics; Numerical simulation; Physical modeling; Physics; Stellar winds

Disciplines

Astrophysics and Astronomy | Physical Sciences and Mathematics | Physics | Stars, Interstellar Medium and the Galaxy

File Format

pdf

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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