Protostars and Planets VI, Heidelberg, July 15-20, 2013

Poster 2B031

Circumbinary Disk around Eccentric Binary

IMAEDA, Yusuke (Tokyo TECH)

Most stars are born as a binary system or a multiple system. Usually, its orbit is eccentric and the binary is tidally interact with the surrounding gas disk for a long time. We present the numerical results of the long-term interaction between the eccentric binary and the circumbinary disk. Instead of a direct calculation of the fluid equation, we solved a time averaged evolution equation for the gas orbital element. The assumption we made is that the change of orbital parameter for the gas element is much longer than the orbital period of the corresponding semimajor axis. The dominant motion of the gas disk is Keplerian rotation around the mass center. The gravity force deviation and the pressure force are much smaller than the dominant gravity. Thus, the above assumption is valid. This indicates that the orbital change in one orbital period can be neglected and the gas disk can be treated as an assembly of gas rings. Time averaged evolution equation for the gas orbital element is calculated over these gas rings. The results shows the eccentric binary makes the circumbinary disk also eccentric. Some eccentricity and pericenter gradient structure are formed in the disk, which can make the banana-like density structure in the circumbinary disk, if the gradient becomes sufficiently large. We also calculate the mass accretion from the eccentric circumbinary disk to the eccentric binary stars with Godunov SPH. Various disk eccentricities are considered. The results shows that the mass accretion rate drastically increases if the disk eccentricity is high enough. This indicates the opportunity that rapid gas dissipation occurs when the disk becomes eccentric by the secular evolution around the eccentric binary.

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