[en] The thesis investigates the nature of non-synchronous motions in members of close binary stars under the influence of gravitational and magnetic fields existing in these systems, and the evolution of such motions in different classes of binaries. Largely convective stars are considered and a solution is found for the fluid flow associated with the non-synchronous rotation of such a secondary in a close binary system, taking tidal and rotational forces into account. The tidal velocity field is calculated for a low mass white dwarf secondary star in a twin - degenerate binary. It is found that the synchronisation times can be comparable to the lifetime of the binary so that some asynchronism may remain present. (U.K.)

[en] Magnetically controlled mass transfer is considered in an AM Herculis-type binary. An expression is derived for the accretion torque on the primary star for the case in which its magnetic moment lies in the orbital plane. Stable orientations are found at which this torque vanishes. Other orientations are found which may restrict mass transfer, and a possible connection with the low states observed in these systems is discussed. (author)

[en] The problem of the maintenance of synchronism in the AM Herculis binaries is considered. It is shown that a magnetic field intrinsic to the secondary star can lock the primary in stable corotation with the orbital motion. The values of the field required are found to be quite plausible for a rotating star with a deep convective envelope. Such a field could be generated by dynamo action, or possibly be rooted in a small radiative core in the secondary. For a given accretion rate and orbital parameters, the synchronous orientation of the primary cannot be predicted without knowledge of the strength and orientation of the secondary's magnetic field. (author)

[en] The interaction of a magnetic neutron star with an accretion disc is considered, in the axisymmetric case. Stellar poloidal field penetrates the disc and acts as a source of toroidal field, generated by material shears. For typical neutron star magnetic moments the back reaction of the field on the main part of the disc is small. However, in the inner parts of the disc magnetic stresses become comparable to material stresses and the angular velocity of matter tends towards that of the star. Magnetic field solutions are found for two forms of diffusion coefficient and for two angular velocity distributions. These solutions are used to derive the magnetic torque on the star as a function of its rotation rate. Magnetic and accretion torques are compared and expressions are found for the time evolution of the stellar angular velocity and the equilibrium period at which the torques cancel. (author)

[en] The spin evolution of the magnetic primary stars in the 10 known AM Herculis binaries is investigated, using the theory formulated in a previous paper. It is found that, in all cases, magnetic dissipation in the convective secondary can synchronize the primary if it operated before mass transfer began, provided that the initial degree of asynchronism is not excessively large. This dissipation mechanism can also explain a small degree of asynchronism of the primary if accretion began before synchronization was achieved, or if accretion broke a previously attained synchronous state. This slightly asynchronous state exists provided that the mass of the primary is not appreciably greater than 0.8 Msolar masses. (author)

[en] The magnetic field induced in the secondary by an asynchronous magnetized primary in an AM Herculis-type binary system is calculated. The resulting dissipation in the secondary leads to a spin down of the primary star towards synchronism with the orbit. It is found that as long as mass transfer is occurring exact synchronism cannot be achieved. At best the primary approaches a stable equilibrium state in which it rotates slowly relative to the orbit. This qualitative picture is independent of the magnetic diffusivity. (author)

No abstract available

[en] The tidal velocity field is calculated for an initially non-rotating low mass white dwarf secondary in a twin-degenerate binary. These motions are used to find the tidal torque on the secondary, to first order in the orbital frequency, and an expression is derived for the synchronization time. For a lobe-filling secondary the synchronization time has a weak dependence on the mass and luminosity of the star, and for the binary G61-29 is found to be of the same order as the estimated lifetime of the system. It is emphasized, however, that tidal excitation of non-radial oscillatory modes in the secondary may significantly shorten the synchronization time. (author)

[en] Angular momentum transfer due to three-dimensional magnetically channelled accretion flows in cataclysmic binaries is considered. The white dwarf experiences a torque due to the twist in that part of its magnetic field which interacts with the accretion stream. The channelling process can also enhance angular momentum exchange between the stream and the orbit by increasing the gravitational torques. The components of the accretion torque are calculated for an arbitrary static magnetic orientation of the white dwarf, and their variation with orientation is presented. For high inclinations of the accreting pole to the orbital plane the component of the accretion torque parallel to this plane can be comparable to its perpendicular component. It is shown that the parallel component of the torque is still significant relative to the perpendicular component if material links to the white dwarf's magnetic field well away from the L₁ region. (author)

[en] Conditions are derived for which the white dwarf component in an AM Herculis binary can attain synchronism with the orbit in the presence of accretion. A stable locking mechanism must exist and, for the case of an initially over-synchronous white dwarf, there is a maximum value of the magnetic diffusivity of the secondary, eta₀, above which exact corotation cannot be attained. In the absence of a locking mechanism the primary will reach a slightly asynchronous state with a typical synodic period of a few tens of years. If eta is significantly less than eta₀ the instantaneous angular velocity of the primary in this state will vary about a central value. (author)