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Paper: Algol Evolution with Spin-down Mechanisms and Systemic Mass Loss
Volume: 482, 10th Pacific Rim Conference on Stellar Astrophysics
Page: 127
Authors: Deschamps, R.; Siess, L.; Davis, P. J.; Jorissen, A.
Abstract: Mass and angular momentum transfers, in semi-detached binaries and especially Algol-type variables, can spin the accreting star up to its critical Keplerian spin velocity. The fate of the gainer star and the subsequent evolution of the binary is uncertain: does mass accretion stop or does a spin-down mechanism act? Moreover, there is growing evidence that Algol systems are non-conservative. However, the mechanism behind this systemic mass loss is unknown. We investigate these two problems (critical rotation of the gainer and non-conservative evolution) with the state-of-the-art binary star evolution code Binstar. Specifically, we follow the orbital and stellar spin evolution of the system taking into account all the torques applying on the stars. We also study the ballistic motion of the accretion stream when it impacts onto the gainer star and forms a hotspot. We find that tides are inefficient during the mass transfer phase and that only a strong magnetic field of the order of 3 kG can maintain the sub-Keplerian rotation of the gainer. The star-disc boundary-layer model prevents the star from exceeding its Keplerian rotation but strongly alters the orbital parameters. Finally, the formation of a hotspot leads to strong mass loss, where up to 15% of the total mass of the system can be expelled.
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