Accretion onto Binary YSOs through Gap from Their Circumbinary Disk

Tomoyuki Hanawa, Yasuhiro Ochi, & Koichi Ando

We have examined gas accretion onto YSO binary from the circumbinary
disk on the basis of 2D numerical simulations of very high spatial
resolution.  The binary was assumed to have either a circular or
an elliptic orbit.  At the initial stage, the inner radius of
the circumbinary disk is 1.75 times larger than the mean
separation of the binary and the disk rotates with the Keplerian
velocity.  We have confirmed that gas accretes from the circumbinary
disk through L2 point onto the binary.  The gas accretes mainly
onto the primary after circulating half around the secondary.
This means that the accretion decreases the mass ratio.
The accretion through gap is due to resonantly excited spiral
shock waves.  The most highly excited spiral waves have the
angular velocity of Omega*/4, where Omega* denotes the binary
angular velocity.  Since they have two arms, the accretion rate
changes with the angular frequency of (3/2) Omega* even when
the binary has a circular orbit.  This implies that the
accretion rate of YSO changes semi-regularly if it is a member
of binary.