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Title:
Accretion and Structure in the SW Sextantis Stars
Authors:
Hoard, Donald Wayne
Affiliation:
AA(UNIVERSITY OF WASHINGTON)
Publication:
Thesis (PHD). UNIVERSITY OF WASHINGTON , Source DAI-B 59/03, p. 1155, Sep 1998, 215 pages.
Publication Date:
09/1998
Category:
Physics: Astronomy and Astrophysics
Origin:
UMI
Comment:
Publication Number: AAT 9828494; Advisor: SZKODY, PAULA
Bibliographic Code:
1998PhDT........10H

Abstract

The SW Sextantis stars are cataclysmic variables (CVs) sharing properties that set them apart from other CVs. These include: strong He II λ4686 emission, velocity curves implying asymmetric disk emission, and variable line profiles displaying a transient absorption feature at specific orbital phases. A number of mechanisms have been proposed to explain these characteristics including (non-disk) circumstellar material, a bipolar disk wind, a white dwarf magnetic field, and coherent accretion stream overflow across the disk, but none has been completely satisfying. I present the results of new photometric and spectroscopic observations of seven SW Sex stars, including Doppler tomogram mapping of emission regions in these systems. These observations, along with recent advances in simulations of accretion disks, suggest a scenario in which the accretion stream undergoes a violent impact with the disk edge. Depending on the mass transfer rate in the stream, the impact site will either cool efficiently (low M) and allow substantial material to flow directly over the disk, or will cool inefficiently (high M) and form a prominent bright spot at the impact site with hot stream material swept 'downstream' along the disk edge. In the former case, non-axisymmetric vertical structure develops in the disk at the terminus of the stream overflow (accounting for absorption seen at φapprox0.5), while in the latter case vertical structure is built up along the disk edge (accounting for absorption at φapprox0.8). The absorption feature phasing in different SW Sex stars implies M decreases as P orb decreases (as expected during CV evolution), but it is not clear whether normal CV evolution can drive changes in M rapidly enough to generate the onset of the SW Sex phenomenon in the narrow range of orbital period they occupy (P orb=3[-]4 hr). I present a gallery of new and archived IUE spectra of the SW Sex stars that display the typically strong UV resonant scattering lines seen in these CVs. The orbital-phase dependence of UV spectral characteristics in UU Aquarii is investigated through a time series of archived IUE spectra, and provides additional evidence of asymmetric structure in this system. The scBINSYN light curve and spectrum modeling package for binary stars has been modified for application to CVs. First results for several SW Sex stars are shown and planned future improvements to the scBINSYN routines are described.
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