Structure and evolution of rotationally and tidally distorted stars

Publications of the Astronomical Society of Japan

Lü

Jing-Zhou

2011

The model of anisotropic loss of the mass and angular momentum is constructed and the non-conservative evolution of the binary system is investigated in this paper. The joint effects of the centrifugal force and tidal force cause the configurations of two components to become triaxial ellipsoids. The high-order disturbing potential, which includes the rotational and tidal distortions, is applied to describe the local gravity in a close binary system. The g eff (Â, ')-effect dominates the mass-loss distribution in the massive O-type star. Both the g eff (Â, ')-effect and the Ä-effect have an important influence on the equatorial ejection, and the Roche lobe overflow and the H-shell burning occur earlier in the rotational models. The rotation and tide can intensify the mass loss before mass overflow, and the rate of stellar wind goes down, resulting from a decrease of the luminosity in the subsequent stages. The highorder disturbing potential and other associated physical factors may significantly affect the Roche lobe and might be possible to drive the non-conservative mass transfer process when the stars approach the break-up rotation. Rotation and tide can allow the primary to shift towards the blue side of the HR diagram and modify the thermal relaxation time-scale in the slow phase of the mass transfer in Case A. The star attempts to attain thermal equilibrium and displays a slightly cyclical expansion and contraction. When stellar wind was taken into consideration in the model, the secondary star accreted less mass than the model without stellar wind.

Section: The High-order Perturbing Potential In the Rotating Binary S...mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Wind Anisotropy and Angular Momentum Loss in a Massive Rotating Binary System

Publications of the Astronomical Society of Japan

Lü

Jing-Zhou

2011

“…In a rotating binary system, the joint effect of rotation and tides modifies the shapes of two components from the perfect sphere to triaxial ellipsoids (Landin et al 2009;Song et al 2009Song et al , 2011Huang 2004). Eggleton & Kiseleva (1998) have presented the equations governing the quadrupole tensor of a star distorted both by rotation and by the presence of a companion in a possibly eccentric orbit.…”

Section: Introductionmentioning

confidence: 99%

The structure of critically-rotating accreting stars

Wang

et al. 2017

A&A

Self Cite

Context. The structure characteristics of the critically-rotating accretor in binaries are investigated in this paper, on the basis of the potential function including rotational and tidal distortions. Aims. Our aim is to investigate the structure of the accretor when the accreting star reaches the critical velocity. Methods. In this paper, we have implemented the prescription described by Kippenhahn & Thomas (1970, Proc. IAU Colloq., 4, 20) and Landin et al. (2009, A&A, 494, 209).Results. The traditional model merely included the hydrodynamical effect of rotation. When comparing this model with ours, we find that it is very necessary for the rapidly rotating accreting star to include the gravitational potentials from tides Ψ tide , and the distortions of the star resulting from rotation Ψ dis,rot . Furthermore, we find that the mean effective gravitational acceleration can be decreased in the distort model, and the star shifts towards low temperature and low luminosity. Rotation and tides can extend the convection zone below the surface, and reduce the convective core in the center of stars due to the Solberg-Hoiland criterion. Rotational distortions derived from Ψ dis,rot can intensify the critical velocity whereas the tide force derived from Ψ tide tends to reduce the critical velocity. Rapid rotation induced by mass transfer also causes the central temperature to decrease, and triggers efficient mixing which can significantly modify the H-profile.

“…These physical processes are active in both single and binary stars. They may have important consequences on observable properties (Langer & Maeder 1995;Heger & Langer 2000b;Song et al 2009Song et al , 2011. They can mix the material of the core and envelope, leading, among other consequences, to nitrogen enrichment at the stellar surface.…”

Section: Introductionmentioning

confidence: 99%

Close-binary evolution

Maeder

Meynet

et al. 2013

A&A

Self Cite

Context. Tides are known to play an important role in binary evolution, leading in particular to synchronization of axial and orbital rotations and to binary mass transfer. Aims. We study how tides in a binary system induce some specific internal shear mixing that can substantially modify the evolution of close binaries prior to mass transfer. Methods. We constructed numerical models accounting for tidal interactions, meridional circulation, transport of angular momentum, shears and horizontal turbulence. Furthermore, we considered a variety of orbital periods and initial rotation velocities. Results. Depending on orbital periods and rotation velocities, tidal effects may spin down (spin-down case) or spin up (spin-up case) the axial rotation. In both cases, tides may induce a high internal differential rotation. The resulting tidally induced shear mixing is so efficient that the internal distributions of angular velocity and chemical elements are highly influenced. The evolutionary tracks are modified, and in for spin down as well as for spin up, large amounts of nitrogen can be transported to the stellar surfaces before any binary mass transfer. Meridional circulation, when properly treated as a advection, always tends to counteract the tidal interaction, tending to spin up the surface when it is braked down and vice versa. As a consequence, the times needed for the axial angular velocity to become equal to the orbital angular velocity may be longer than given by typical synchronization timescales. Moreover, because of the meridional circulation some differential rotation remains in tidally locked binary systems.