Abstract
We present high spatial resolution (750 AU at 250 pc) maps of the B1 shock in the blue lobe of the L1157 outflow in four lines: CS (3-2), CH3OH (3_K-2_K), HC3N (16-15) and p-H2CO (2_02-3_01). The combined analysis of the morphology and spectral profiles has shown that the highest velocity gas is confined in a few compact (~ 5 arcsec) bullets while the lowest velocity gas traces the wall of the gas cavity excavated by the shock expansion. A large velocity gradient model applied to the CS (3-2) and (2-1) lines provides an upper limit of 10^6 cm^-3 to the averaged gas density in B1 and a range of 5x10^3< n(H2)< 5x10^5 cm^-3 for the density of the high velocity bullets. The origin of the bullets is still uncertain: they could be the result of local instabilities produced by the interaction of the jet with the ambient medium or could be clump already present in the ambient medium that are excited and accelerated by the expanding outflow. The column densities of the observed species can be reproduced qualitatively by the presence in B1 of a C-type shock and only models where the gas reaches temperatures of at least 4000 K can reproduce the observed HC3N column density.
Highlights
Bipolar molecular outflows are one of the observable signatures of the early stages of the star formation process producing strong alterations of the protostellar environment both dynamically, accelerating the gas, and chemically, activating the high temperature chemistry in the shocked gas
We found that the percentage of the missing flux depends on the velocity: for the high velocity gas (v < - 6 km s−1) Plateau de Bure (PdB) recovers 100% of the flux while for the low velocity gas (v > - 6 km s−1) the flux measured at PdB is ∼ 62% of the IRAM flux
It is worth noting that while the CS and CH3OH emission have a morphology very similar to that observed in lower excitation lines (with CH3OH brighter in the west-side clumps (B1b) and CS brighter in the east-side clumps (B1a, B1c)), HC3N and H2CO are brighter in the north-side clumps (B1a), similar to what is observed for CH3CN (8K –7K ) (Codella et al 2009)
Summary
Bipolar molecular outflows are one of the observable signatures of the early stages of the star formation process producing strong alterations of the protostellar environment both dynamically, accelerating the gas, and chemically, activating the high temperature chemistry in the shocked gas. Because of its chemical richness and its clear morphology, the L1157 outflow is an excellent laboratory to study the shock generated by protostellar outflows It was observed by the Chemical Herschel Survey of Star forming regions (CHESS) Herschel Key Program (Ceccarelli et al 2010) as prototype of chemically active outflows and it was used to test shocks models by many authors Gusdorf et al 2008a; Flower & Pineau des Forets 2010, 2012) The results of this extensive modeling activity on L1157–B1 testify the complexity of this region where multiple shock types are acting.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
