The Disk Substructures at High Angular Resolution Project (DSHARP): IV.
  Characterizing substructures and interactions in disks around multiple star
  systems
  To characterize the substructures induced in protoplanetary disks by the
interaction between stars in multiple systems, we study the $1.25\,$mm
continuum and the $^{12}$CO$(J=2-1)$ spectral line emission of the triple
systems HT Lup and AS 205, at scales of $\approx 5\,$au, as part of the 'Disk
Substructures at High Angular Resolution Project' (DSHARP). In the continuum
emission, we find two symmetric spiral arms in the disk around AS 205 N, with
pitch angle of $14^\circ$, while the southern component AS 205 S, itself a
spectroscopic binary, is surrounded by a compact inner disk and a bright ring
at a radius of $34\,$au. The $^{12}$CO line exhibits clear signatures of tidal
interactions, with spiral arms, extended arc-like emission, and high velocity
gas, possible evidence of a recent close encounter between the disks in the AS
205 system, as these features are predicted by hydrodynamic simulations of
fly-by encounters. In the HT Lup system, we detect continuum emission from all
three components. The primary disk, HT Lup A, also shows two-armed symmetric
spiral structure with a pitch angle of $4^\circ$, while HT Lup B and C, located
at $25$ and $434\,$au in projected separation from HT Lup A, are barely
resolved with $\sim5$ and $\sim10\,$au in diameter, respectively. The gas
kinematics for the closest pair indicates a different sense of rotation for
each disk, which could be explained by either a counter rotation of the two
disks in different, close to parallel, planes, or by a projection effect of
these disks with a close to $90^\circ$ misalignment between them.
