Wonnacott, David; (1991) The Algol-type binary CX Draconis: Numerical models of ultraviolet observations. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

International Ultraviolet Explorer satellite spectra of the Algol-type interacting binary system CX Dra (B2.5 Ve + F?) have been analysed in detail, revealing a new phenomenon, to whit, CX Dra possesses a matter stream which at certain orbital phases disappears from the line-of-sight almost entirely. This has been dubbed 'stream dipping'. Two possible alternative interpretations of these observations have been examined. Either the stream is undergoing a rapid change in its ionization balance, or the stream is collapsing towards the orbital plane as it gains speed. More complex models involving, for example, variable stellar winds or distortion of the stream trajectory by magnetic forces can be excluded to varying degrees by the velocity structure seen in the resonance lines. Several scale-independent numerical models of interacting binary systems have been generated and applied to CX Dra in order to gain an insight into the geometry which is responsible for this effect. U Cep, with its well-known system parameters, has been used as a benchmark for the models. Those models with inviscid streams have failed to reproduce the observations, but the viscous streams, modelled using a cell-averaging technique, reproduce not only the observed velocity structure but the phase-dependency of the profiles too. Profile fitting then yields the chemical composition of the stream (these results indicate a high degree of CNO-processing), and allows a lower limit to be placed on the inclination of the orbital plane. The density structure of the models has also been used to predict the variations Attention is drawn to the inclusion of an addendum which contains the results of a detailed investigation into the properties and possible failings of the numerical model employed in this work, in particular to the non-conservation of angular momentum. The results derived from this model are, however, largely insensitive to this flaw.

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