Structure and kinematics of a protostar : mm - interferometry of L 1157

We present high angular resolution (2.5′′) interferometric images of 13CO J = 1→ 0 , C18O J = 1→ 0 , and λ 2.7 mm continuum emission around L1157-mm, a suspected protostar powering an energetic molecular outflow. The continuum emission consists in two distinct components. The Class 0 object L1157-mm is seen as a compact source of size ≤ 1′′ (440 AU) and mass ' 0.2M , which is marginally resolved and elongated perpendicular to the outflow axis. In addition, spatially-extended low-level emission is observed and likely arises at the heated edges of the cavity excavated by the outflow in the surrounding envelope. Simple modelisation shows that such an interacting structure can explain the observed morphology and the spectral energy distribution of the source. The line observations indicate that 13CO mostly originates from the envelope and the limb-brightened edges of the outflow, whereas the C18O emission is more directly associated with the compact continuum source.Weak evidence for rotation has been found. Comparison of the two line tracers shows proeminent redshifted self-absorption in the 13CO spectrum which is very suggestive of infall motions. The infalling medium seems to be confined in a large (a few thousands AU) flattened structure. These observations provide a quite detailed description of the structure of a Class 0 protostar, which appears to have a complex vicinity where the outflowing and accreting phenomena are closely linked together.