  We have imaged the circumstellar envelope around the binary protostar L1551
IRS 5 in CS (J=7-6) and 343 GHz continuum emission at ~ 3 arcsec resolution
using the Submillimeter Array. The continuum emission shows an elongated
structure (~ 220 x 100 AU) around the binary perpendicular to the axis of the
associated radio jet. The CS emission extends over ~ 400 AU, appears
approximately circularly symmetric, and shows a velocity gradient from
southeast (blueshifted) to northwest (redshifted). The direction of the
velocity gradient is different from that observed in C18O (J=1-0). This may be
because rotation is more dominant in the CS envelope than the C18O envelope, in
which both infall and rotation exist. The CS emission may be divided into two
velocity components: (1) a "high" velocity disk-like structure surrounding the
protostar, +-1.0 - 1.5 km s-1 from the systemic velocity, and (2) a "low"
velocity structure, located southwest of the protostar, < 1.0 km s -1 from the
systemic velocity. The high-velocity component traces warm and dense gas with
kinematics consistent with rotation around the protostar. The low-velocity
component may arise from dense gas entrained in the outflow. Alternatively,
this component may trace infalling and rotating gas in an envelope with a
vertical structure.
