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Paper: Interaction between the Viscous Decretion Disk and the Neutron Star in Be/X-ray Binaries
Volume: 361, Active OB-Stars: Laboratories For Stellar and Circumstellar Physics
Page: 395
Authors: Okazaki, A.T.; Hayasaki, K.
Abstract: We report on the results from numerical simulations of the interaction between the viscous decretion disk around the Be star and the neutron star in Be/X-ray binaries. For simplicity, both the Be decretion disk and the neutron star accretion disk are assumed to be isothermal and Shakura-Sunyaev's viscosity prescription is adopted. The Be disk is tidally/resonantly truncated at a radius smaller than the periastron distance, except in systems with very high orbital eccentricities and/or large inclination angles. In misaligned systems, the Be disk precesses little when the mass is supplied continuously from the central star, whereas it precesses in the retrograde direction when no mass is supplied. The truncated Be disk in an eccentric orbit makes the mass transfer rate towards the neutron star strongly phase dependent and sensitive to the orbital eccentricity. In highly eccentric systems, a transient accretion disk is formed around the neutron star after every periastron passage. The peak mass-accretion rate in these systems falls within a typical luminosity range of the periodic X-ray outbursts in Be/X-ray binaries. This strongly suggests that, in the framework of the truncated Be disk model for Be/X-ray binaries, periodic X-ray outbursts are a phenomenon most frequently seen in highly eccentric systems.
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