  A new computational scheme is developed to study gas accretion from a
circumbinary disk. The scheme decomposes the gas velocity into two components
one of which denotes the Keplerian rotation and the other of which does the
deviation from it. This scheme enables us to solve the centrifugal balance of a
gas disk against gravity with better accuracy, since the former inertia force
cancels the gravity. It is applied to circumbinary disk rotating around binary
of which primary and secondary has mass ratio, 1.4:0.95. The gravity is reduced
artificially softened only in small circular regions around the primary and
secondary. The radii are 7% of the binary separation and much smaller than
those in the previous grid based simulations. 7 Models are constructed to study
dependence on the gas temperature and the initial inner radius of the disk. The
gas accretion shows both fast and slow time variations while the binary is
assumed to have a circular orbit. The time variation is due to oscillation of
spiral arms in the circumbinary disk. The masses of primary and secondary disks
increase while oscillating appreciably. The mass accretion rate tends to be
higher for the primary disk although the secondary disk has a higher accretion
rate in certain periods. The primary disk is perturbed intensely by the impact
of gas flow so that the outer part is removed. The secondary disk is quiet in
most of time on the contrary. Both the primary and secondary disks have
traveling spiral waves which transfer angular momentum within them.

Solar and Stellar Astrophysics