Tidal Torques on Misaligned Protoplanetary Disks in Binary Systems

Tidal Torques on Misaligned Disks in Binary Systems

Authors:

Lubow et al

Abstract:

We extend previous studies of the tidal truncation of coplanar disks in binary systems to the more general case of noncoplanar disks. As in the prograde coplanar case, Lindblad resonances play a key role in tidal truncation. We analyze the tidal torque acting on a misaligned nearly circular disk in a circular orbit binary system. We concentrate on the 2:1 inner Lindblad resonance associated with the m=2 tidal forcing (for azimuthal wavenumber m) that plays a major role in the usual coplanar case. We determine the inclination dependence of this torque, which is approximately cos^8(i/2) for misalignment angle i. Compared to the prograde coplanar case (i=0), this torque decreases by a factor of about 2 for i = pi/6 and by a factor of about 20 for i=pi/2. The Lindblad torque decreases to zero for a tilt angle of pi (counter-rotation), consistent with previous investigations. The effects of higher order resonances associated with m greater than 2 tidal forcing may contribute somewhat, but are much more limited than in the i=0 case. These results suggest that misaligned disks in binary systems can be significantly extended compared to their coplanar counterparts. In cases where a disk is sufficiently inclined and viscous, it can overrun all Lindblad resonances and overflow the Roche lobe of the disk central object.