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Session 76 - Cataclysmic Variables and Accretion Disks.
Display session, Wednesday, January 15
The SW Sextantis stars are a recently identified subclass of novalike cataclysmic variable (CV). These \approx10 systems have orbital periods in the range \sim3--4 hr; they also share a number of peculiar characteristics that set them apart from other CVs. For example, an unusually high level of excitation in their spectra (including prominent He \sc ii \lambda4686 emission); (2) velocity curves of their emission lines that imply non-uniform emission from the accretion disk; (3) single-peaked emission lines in contrast to the expected double-peaked lines typically observed in high inclination disk systems; and (4) their Balmer and He \sc i lines have orbital-phase-dependent profiles characterized by the appearance of a strong absorption feature at specific phases. Since the novalike CVs are thought to be systems with a constant high mass transfer rate, we are investigating the possible origin of the SW Sex phenomeneon in the structure of the prominent accretion disks in these CVs. We present a compilation of new and published data on the SW Sex stars comparing the values of system parameters (such as inclination, component masses, etc.) and a number of observational properties (such as optical and UV line intensities, X-ray flux, etc.). Clues to the geometry of these CVs can be inferred by comparing characteristics among the entire group. For example, the orbital phases(s) at which the absorption feature appears in the Balmer and He \sc i emission lines may depend on the inclination of the system. This relationship, in turn, can be used to deduce the relative vertical extent of the structures in the disk responsible for the absorption.
Program listing for Wednesday