L 1157 : Interaction of the molecular outflow with the Class 0 environment

We present high angular resolution interferometric observations [ ⋆ ] of the dust continuum at 2.7 and 1.3 mm, and of the HC3N (J=12→11) and C 18 O (J=2→1) emission around L1157-mm, a Class 0 object that drives a spectacular molecular outflow. The millimeter dust emission is clearly resolved into two components, a flattened compact source of ∼450×250 AU at 1.3 mm, and mass ∼0.1 M⊙, plus an extended envelope of ∼3000 AU at 1.3 mm, and mass ∼1.1 M⊙. The millimeter spectral index varies throughout the region, with the lower value found toward the compact protostar, possibly indicating grain growth in the denser regions. A strong interaction between the molecular outflow and the close pro-tostellar environment is taking place and affects the structure of the innermost parts of the envelope. This is shown by the spatial coincidence between the molecular outflow and the dust (1.3 mm continuum) and HC3N emission: both tracers show structures associated to the edges of the outflow lobes. Basically, the global picture sketched for the Class 0 object L1157-mm by Gueth et al. (1997) is supported. We find possible evidence of infall, but we do not detect any velocity gradient indicative of a rotating circumstellar disk. ⋆ Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). 2 Beltrán et al.: The environment of L1157