  We present new high-sensitivity 1.3 mm bolometer observations of the young
outflow L1157. These data show that the continuum emission arises from four
distinct components: a circumstellar disk, a protostellar envelope, an extended
flattened envelope --the dense remnant of the molecular cloud in which the
protostar was formed--, and the outflow itself, which represents ~20% of the
total flux. The outflow emission exhibits two peaks that are coincident with
the two strong shocks in the southern lobe of L1157. We show that the mm
continuum is dominated by thermal dust emission arising in the high velocity
material. The spectral index derived from the new 1.3 mm data and 850 mu
observations from Shirley et al. (2000), is ~5 in the outflow, significantly
higher than in the protostellar envelope (~3.5). This can be explained by an
important line contamination of the 850 mu map, and/or by different dust
characteristics in the two regions, possibly smaller grains in the post-shocks
regions of the outflow. Our observations show that bipolar outflows can present
compact emission peaks which must not be misinterpreted as protostellar
condensations when mapping star forming regions.
