2004ApJ...616L..15T

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" resolution using the Submillimeter Array. The continuum emission shows an elongated structure (∼220x100 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 can be divided into two velocity components: (1) a ``high''-velocity disklike structure surrounding the protostar ±1.0-1.5 km/s from the systemic velocity, and (2) a ``low''-velocity structure located southwest of the protostar less than 1.0 km/s 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.