2 00 4 Submillimeter Array Observations of L 1551 IRS 5 in CS ( J = 7 – 6 )

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 (∼ 220× 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 CO (J=1–0). This may be because rotation is more dominant in the CS envelope than the CO 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 from the systemic velocity, and (2) a “low” velocity structure, located southwest of the protostar, < 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. Subject headings: ISM: individual (L1551 IRS 5) — ISM: molecules — stars: disk — stars: formation Harvard-Smithsonian Center for Astrophysics, Submillimeter Array Project, 645 North A’ohoku, Hilo, HI 96720, U.S.A. e-mail: [email protected] Academia Sinica Institute of Astronomy and Astrophysics, 645 North A’ohoku, Hilo, HI 96720, U.S.A.; [email protected] Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, U.S.A. Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 106, Taiwan Taeduk Radio Astronomy Observatory, Korea Astronomy Observatory, Hwaam 61-1, Yuseong, Daejeon, 305-348, Korea Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 21008, China