Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt........19a&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF COLORADO AT BOULDER, 1994.Source: Dissertation Abstracts International, Volume: 55-10, Section: B,
Astronomy and Astrophysics
Astrophysics
Scientific paper
This thesis examines the dynamical role of radiation in two astrophysical environments: (a) shear layers between astrophysical jets and their surrounding medium and (b) broad absorption line (BAL) regions of QSOs. At the interface between a jet and its ambient medium, a shear flow forms. In many astrophysical situations it can be shown that viscosity due to momentum transport by photons is much larger than viscosity due to two-body collisions between particles. By solving self-consistently the appropriate boundary layer equations, I have shown that radiation viscosity can have dramatic effects on the shear-flow region of a supersonic jet: the density of the boundary layer is much smaller and its width is much larger than those of a "classical boundary layer." I have applied this formalism to the case of SS 433, and shown that the boundary layer can be visualized as a cocoon of low-density matter around the jet much wider than the jet itself. My research laid the foundations of this field which was unexplored previously. About 12% of QSOs show broad absorption troughs in their spectra, associated with UV resonance lines of highly ionized metals. All of the BALs show significant blueshifts with respect to the centers of the corresponding broad emission lines. The blueshift is commonly attributed to matter flowing toward the observer with velocities of up to 0.1c. One of the most important questions regarding these objects is the nature of the acceleration mechanism. The approach I have taken is to study the feasibility of radiative acceleration. The idea is that momentum deposited by photons during scattering in the prominent resonance lines is accelerating the absorbing material. By comparing BAL flows to radiatively driven O-star winds, I demonstrate the feasibility of radiative acceleration in BAL flows, and then construct dynamical models that allow us to predict the resultant BAL profiles. Finally, I have used these dynamical models (and especially an important nonlinear effect I discovered while analyzing them) to explain the double trough observed in the C IV 1549 BAL of many BALQSOs. This is the first quantitative model that can explain dynamically any of the observed features of BAL profiles.
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