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| Paper: |
The Effect of Tidal Friction and Quadrupolar Distortion on Orbits of Stars or Planets in Hierarchical Triple systems |
| Volume: |
154, Cool Stars, Stellar Systems and the Sun: Tenth Cambridge Workshop |
| Page: |
2118 |
| Authors: |
Kiseleva, L. G.; Eggleton, P. P. |
| Abstract: |
In hierarchical triple stars, such as lambda Tau and beta Per the combination of a) fluctuating eccentricity due to the third body and b) tidal friction, mainly within the close pair, which tries to remove such fluctuations, can lead to potentially large but slow secular changes in orbital parameters. We model the orbits of both the above systems using a force law which includes a combination of point-mass gravity, quadrupolar distortion of each star by the other two, and a dissipative tidal-friction term. For lambda Tau we find a preferred model where expansion of the inner orbit due to mass transfer on a nuclear timescale is balanced by contraction because tidal friction transfers angular momentum from the inner to the outer orbit. In beta Per, the two orbits are nearly orthogonal (i=100 deg), and the effect of the third star would periodically increase the inner eccentricity up to nearly unity if we neglect the effects of quadrupolar distortion and tidal friction. In fact, in beta Per quadrupolar distortion alone can almost completely suppress the inner eccenticity fluctuations. In a hypothetcal zero-age state of this system, when the inner binary can be supposed to be well-detached, we find large fluctuations in eccentricity which, on being damped by tidal friction, lead to shrinkage of the inner orbit on a surprisingly short timescale. However, the shrinkage is halted by the fact that as the inner pair becomes closer they become more distorted: this quadrupolar distortion leads to apsidal motion which prevents further large fluctuations in eccentricity. In hypothetical cases of nearly orthogonal triple systems with one component of the close pair being a Jupiter-like planet, the combined effect of quadrupolar distortion and tidal friction may reduce the fluctuations of the inner eccentricity, and in some cases the Jupiter orbit can in principle be shrunk quite drastically over a suitably long interval of time. This is potentially important for the long-term evolution. |
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